Electricity, Part Two

AC/DC jokes aside, this is important current information.

AC/DC jokes aside, this is important current information.

So, by now, I assume you have read the previous post, Electricity: Part 1, at least five or six times to really grasp the intricacies of what electricity is and how it relates to the transfer of energy. You may also have read it once, fallen asleep and Google led you back here to part two against your will. Either way, I hope you enjoy the following discussion on the topics of electrical loads, alternating vs. direct current, single phase vs. three phase power, and the generation of electrical energy. Please enjoy it, I’ve lost a lot of sleep working on it. Sorry; that was supposed to be an inner monologue comment.

At this time, I’d like to ask for patience from those who are not big fans of geometry, trigonometry or other forms of mathematics. I’ll try and keep some of these concepts as simple as possible, while trying not to offend the majority of engineers, mathematicians or academics by being partially or even totally wrong. I will also try and keep the electrical jokes to a minimum. This subject is not for everyone so I make no promises.


In Part One, I introduced the idea of an electrical circuit. Electrons and the electromagnetic energy they carry will not flow from one pole to another unless their path is fully connected. Flipping a switch in your home either breaks the circuit (literally creates a gap in the wiring), or completes an electrical circuit and allows the flow of electrons. The following images show the simplest of circuits; one with a battery (a power source), wiring (path) and a light bulb, where the flow of current travels from one terminal of the battery, through the wire into the light bulb, causes the bulb’s filament to glow brightly and then continues on through the wiring to the battery’s opposite terminal. The second image is similar to the first, but the power source in this case is an AC Generator, so the flow of electrons change directions at a certain frequency. We will get into the differences between AC and DC later in the discussion.

Direct Current Circuit

AC Current Circuit

Every electrical circuit needs both a power source and something to resist the flow of electrons. Without some resistance, electrons will flow very quickly through a conductor. Given no speed limit (and no fear), drivers on an interstate would drive as fast as they can. If everyone drove like they were qualifying for the Daytona 500, you can imagine how many accidents would occur and the entire transportation system would break down. Electrical current is no different. If permitted, electrons will move as fast as possible in larger numbers and would eventually exceed the wire’s ability to handle the heat generated by the flowing electrons. When this happens, the wire can actually melt or catch its insulation on fire. A common cause for this type of excessive current is a “short circuit” where someone directly connects the two poles of a battery, or when a current carrying conductor (wire) comes in contact with metal objects or people; allowing current to flow unimpeded into them or into the ground. Resistance keeps the flow of electrons in check. For any normally operating circuit, this is not a problem since the entire point of electricity is to supply energy to some kind of device or equipment. The component of a circuit that utilizes the energy being transported and provides some resistance is known as a load.

Loads can be categorized into many different groups, but the most common are resistive, capacitive, and inductive. I know, the terms are beginning to sound complex and you may have started dozing off, but think of them as loads that resist the flow, capture the flow, or induce their own flow of electrons. It’s an over-simplification, but it works for me.

Types of Loads


Resistive loads are some of the most commonly known (or thought of), and are characterized by the fact they create heat (and/or light), the voltage and current are in phase with each other (more on phase later), and they do not generate their own magnetic field. Common resistive loads would include incandescent light bulbs and most electric heaters.

Resistive loads take advantage of the fact that some metals are conductive, but put up a fuss when they are energized. Much like a teenager when they are asked to clean their room; they are fully capable of doing so, but they sure put up a lot of resistance to do so, and cause their parents tempers to rise. I know it’s a thin comparison, but as a parent, its painfully relevant.

Certain elements such as Tungsten, used in common incandescent light bulb filaments, and an alloy used in heating elements called Ni-chrome (a mixture of Nickel and Chromium), are conductive, but when electrical current is passed through them, they emit much of the energy as either light, heat or both. Given the fact that only one of these results is typically desired, the balance of the energy used is wasted. This makes resistive loads very simple, but also very inefficient.


Devices used as capacitive loads are commonly referred to as capacitors. I know; big shock (the puns don’t stop here folks). Capacitors are capable of storing an electrical charge that can be released at a desired speed and quantity. Capacitors are not unlike a short-term rechargeable battery, but are used to store a large charge that can be released nearly all at once, or released slowly to provide a more even voltage or current. Although used in nearly every electronic device made today that can plug into an outlet, some better-known examples of devices that heavily rely on capacitors would be camera flash-bulbs, defibrillators and joy buzzers (although the last item is not a very safe or nice use of a capacitor, and no I’m not suppressing painful childhood experiences).


Inductive loads can seem more complex, but are one of the essential reasons humans learned how to harness the power of electricity.

As discussed in Part 1 of this post, we learned that passing electrical current through a conductive material creates a magnetic field. In single conductors the field is negligible, but when current is passed through a coil made of some conductive material, a larger magnetic field is created. The exact opposite is also true. If a coil of wire is passed through a magnetic field, it introduces a flow of current in the coil / conductor. Simply put; pass a magnet by a coil you get current in the coil. Energize a coil and you get a magnetic field.

This behavior of inductance is the reason that generators are able to create a flow of electricity and why motors are able to transform electrical energy into mechanical movement. The discussion of inductance is a substantial one on its own, and we could spend hours talking about induced voltage, power factors, and other engineering type stuff, but I’m stopping here. I don’t have the capacitance to go on, so I’m going to focus on how inductance allows for the creation of electricity as we use it in residential and commercial buildings across the world.

I’m a fan of AC/DC, and it’s not just a phase.


Let’s talk about AC, DC, Edison and Tesla (the man, not the car manufacturer).

Thank you to Maggie Ryan Sandford at mentalfloss.com for the following information, and lets be honest; most of the words.

For those geeks like myself that enjoy a bit of scientific history and trivia, this may not be new information, but to everyone else, the story of Alternating Current (AC), Direct Current (DC), Thomas Edison, Nikola Tesla and Niagara Falls sounds like a made-for-TV movie.

Nikola Tesla, a Serbian by parentage, began working for the Continental Edison Company in Paris in 1882. After gaining praise from his supervisor, he was invited to the US to work alongside Thomas Edison himself. Although Edison thought the man’s ideas were “splendid”, he found them “utterly impractical”. Edison and Tesla both worked long hours, were egocentrics and required little sleep (don’t they sound like a lot of fun to be around… wait, that sounds a lot like me… never mind). Their contrasting work and personal styles, mixed with what seems like sleep deprivation, led to many long, grumpy hours in the workshop.

Edison’s least favorite idea of Tesla’s was the concept of using alternating current technology to bring electricity to the people. Edison was much more partial to his own direct current system, and maintained that the lower voltage from power station to the consumer was safer. AC technology allows for the flow of energy to periodically change direction, and is more practical for transmitting massive quantities of energy over long distances. At the time, DC systems only allowed for a power grid within a one-mile radius of the power source (talk about a case of NIMBY: Not In My BackYard). The conflict between the two technologies, as well as Edison and Tesla’s feud, became known as the War of Currents, hence the not so hidden meaning behind the band name AC/DC.

Tesla eventually sold most of his patents to George Westinghouse (not an unfamiliar name to those familiar with power generation), who built one of the first AC power plants at Niagara Falls to power New York City, and then used the same principles to create much of the modern power grid we have today.

Edison wasn’t wrong however, as the higher voltages of AC are not safe or practical for use in smaller consumer electronics or appliances used in the home; hence the myriad of “power supplies” and converters used in our everyday lives. These converters and power supplies change the higher-voltage alternating current into a lower voltage direct current that can be used more effectively.

So AC and DC technology have been around for quite some time, but what is the difference?

Direct Current

Direct Current (DC) is electrical energy supplied at a constant voltage (approximately). DC is normally used at levels of 24 volts and lower, but can be occasionally seen higher. If plotted on a graph of voltage over time, it may look like the following diagram:

Direct Current Graph

DC is pretty much the standard for point-of-use electrical needs in consumer electronics and anything else that requires very precise and consistent current flow. DC loads can be resistive, capacitive and inductive.

Alternating Current

Most of the electric power in the world is AC. Electricians work with AC about 99% of the time, given its wide use in building electrical systems and its ability to transport energy over long distances. One of the biggest advantages of AC is that is can be transformed and DC cannot. A transformer can step up or step-down voltages as needed for certain devices and depending on what stage of transmission the energy is in. As power always equals the voltage times the amperage, a much larger amount of energy can be transmitted at very high voltages without having to increase the amperage (and therefore wire size). Tesla was a very smart man (if not sometimes foolish; can you imagine what he’d be worth if he hadn’t sold his patents).

Although other methods are available, the most common way of producing AC is by rotating a magnetic field past coils of conductive material, producing an electric current (that whole inductance thing again). The same effect can be created by rotating coils around a stationary magnet. In either case, an electric current is produced in the coil. When the coil is closest to the positive pole of the magnet, the maximum voltage is created in a positive direction. As the magnet is rotated further, the voltage drops increasingly faster until it reaches zero at the time the poles of the magnet are the farthest from the coil. As the magnet continues to rotate, the negative pole gets closer to the coil and the voltage in the coil becomes greater in the negative direction. One complete rotation of the magnet results in one “cycle”, where the voltage starts at zero, reaches its maximum positive value, reaches zero again, reaches its maximum negative value and then returns to zero. The term for cycles per second is called hertz. In the United States, AC is normally provided at 60 Hz (60 cycles per second). Just blew your mind a bit didn’t it? I hope it didn’t hertz too much.   Sorry, I couldn’t resistor.   I kill me.

The diagram below shows the relationship between a rotating point on a circle and the resulting rising and dropping of the voltage. This resultant form is known as a Sine wave, and is one of the most commonly seen wave-forms in nature. Sine waves are also seen in radio waves and any other machine with rotating motion.

Single Phase Animation

Single Phase vs Three Phase

Those professionals who deal with commercial projects have heard the term “Three-Phase Power” more than once, and even the typical homeowner has heard things like “120/240”. I’m sure those terms scare even electricians sometimes as electricity should just be on or off right? Why all the rocket science?

Amazingly, it’s not really difficult.

Single phase power is created when you rotate a magnetic field past one or more connected coils. The resulting voltage and current is always “in phase”, and three times every cycle the voltage is zero. If you generate 120 volts of electricity and then add it to 120 volts of electricity in the same phase, you get double the voltage. This is considered “single-phase” power. In typical residential electrical services, the power company brings two conductors that can each carry 120 volts and a neutral. If you connect say a motor to one of the “hot” conductors and the neutral, it will receive 120 volts. If you connect the motor to both hot conductors, you will get twice the voltage: 240V. Refer to the following diagram to see how the coils of a single-phase generator are “tapped” to get 120 or 240 volts.

Single Phase Power Schematic

Three-Phase Power

Three-Phase power is created by rotating a magnetic field past coils that are spaced 120 degrees apart from each other. Why should this make a difference?

Refer to the following diagrams for clarification, but you’ll quickly see that by spacing the coils equally apart, the sine waves created are also exactly 120 degrees apart. This means that when two or more of the phases are connected together, the resulting voltage never drops to zero. Because the voltage in each phase is offset at any one point, the maximum voltage between two or three phases is not double the single-phase voltage of 120, instead it is equal to the maximum voltage times . If the single phase maximum voltage is 120, then the maximum voltage using two or three of the phases is 208V. I could further explain this correlation using vectors and trigonometry, but don’t you think I’ve beaten you up enough at this point?


3-Phase Diagram

Three Phase Power Schematic

Why use three-phase power?

Three-phase connected motors are much more efficient with the same power and can be used to run longer and with less overall work. If every phase is providing voltage at some point, the motor is never without power. Newton’s 3rd law of motion: A object in motion tends to stay in motion. Keep it going and it takes less work to move it!

OK, time for a metaphor!!

Let’s say you were pushing a small child around on a merry-go-round (yes, they were a very popular playground element before lawyers got involved. See Whatever happened to merry-go-rounds?). One person standing in place could push on the merry-go-round once every time it went around and keep it moving. It would slightly slow down before each push, but you could keep it going. Now put ten kids on that same merry-go-round and one person pushing seems a bit daunting; But, if you were to position three adults around the merry-go-round and each one pushed every time the same spot came by, they’d be pushing three times as much and the fun would never stop; well at least until some poor child decided they’d held onto their lunch long enough. As I’ve said before; metaphors have their limits.

Three phase power is generally limited to commercial use due to the higher number of conductors, and commonly higher voltages, but is nonetheless very common and much more efficient.

Ok, if you have made it this far, I commend your perseverance (or stubbornness). If you understand everything I’ve talked about; please call and re-explain it to me. I may have dozed off in the middle while typing. For your moment of Zen, please enjoy the following animation of a full three-phase genset I modeled. It shows the parts flying away in fantastic fashion. I will try and elaborate on the various parts of the genset in a later post, but for now, enjoy the model and animation that was way more complicated than necessary.

Thank you.


All graphics and animations in this post, with the exception of the two photos were created by DFD Architects, Inc., ©2018 DFD Architects, Inc. ALL RIGHTS RESERVED. No image, video or animation on this post may be reproduced, transmitted, stored, or used in any form without the prior written permission of DFD Architects, Inc. I’m not kidding.

Gracious Acknowledgements to the following sources for information and selected passages, I couldn’t have written this without their guidance or copying their words:

Delmar’s Standard Textbook of Electricity, Sixth Edition. By Stephen L. Herman. Copyright 2016, Cengage Learning. Kindle Edition.

AC/DC: The Tesla-Edison Feud, by Maggie Ryan Sandford, July 10, 2012. http://www.mentalfloss.com


Thank you especially to my father, John D. Gillen, for passing along just enough of his electrical engineering expertise to make me a geek but remain somewhat socially acceptable.

p.s., I’ll buy a beer for the first (over 21 years of age) person in the State of Texas to correctly identify the location of the facility on the cover image (location name and affiliation). Geeks have to stick together! (Follow up: I’m proud to say my father was the first to get this correct; Extra points to Loyd Dittfurth for also identifying exactly where the image itself came from). For those who still haven’t gotten it; its in a cold and snowy place far far away.

Electricity: Part One

The first in an energetic series of posts on what electricity is and how it’s used, generated and distributed.

We don’t consume electricity; we use energy; transforming it into different forms to make our world brighter, warmer (or cooler) and make work easier. We strive to conserve and efficiently use energy, but in the end, we really only change energy from one form to another. Energy never goes away; it just finds another job to do.

If electricity is only the transportation system for the energy we use, then what is electricity and how does it work?

Although the Money Pit is one of my favorite movies, here is an example of how electricity does NOT behave.


In the simplest of terms, electrical current is the excitement and flow of electrons. To understand what that means, we need to start with the most basic building block of all matter: the atom. All matter is made from a combination of atoms (either of one kind or multiple). Any substance that cannot be separated into a simpler substance by chemical means is considered an element. All known elements are cataloged within the ‘Periodic Table of Elements’, a table that has stressed out generations of high school chemistry students. The periodic table of elements describes the individual atomic characteristics of each element, and knowing those characteristics gives us more insight into how they all behave with each other. It’s not unlike knowing the personality types of your friends and co-workers.

The Periodic Table of Elements
Each atom is composed of three basic particles: the electron, proton and neutron. Protons and Neutrons are located in the atom’s nucleus, with the electrons orbiting around in a series of concentric “shells”. Science has uncovered even smaller particles that make up and hold together each atom’s structure, but for our purposes it is the negatively charged electrons (or their absence) that hold the secrets of electricity.

Early scientists such as a Frenchman by the name of Charles Dufay realized that certain materials became attracted to certain objects, but were repelled by others. The forces of attraction and repulsion are described as either a positive or negative charge. As neutrons have no charge, each atom’s nucleus has a net positive charge. As Paula Abdul’s 1988 hit described, “We come together, cuz opposites attract”. Objects with similar charges are repelled from each other, and those with opposite charges are attracted to each other.

At this point, I know that many readers are beginning to have flashbacks to early childhood science class and are wondering, “Where is he going with this? It’s about as exciting as watching paint dry.”

Excitement is exactly what electricity is all about. The outer shell (known as valance electrons) of each atom contains between one and eight electrons. Each atom seeks stability by filling up its outer shell with all eight; a nice calm retirement of sorts. Some atoms like the noble gases Argon and Xenon start out with their outer shells full; they’re calm, unexciting and don’t over-react. Other elements such as gold, silver and copper have only one electron in their outer shell and are more than willing to dance the night away in an attempt to lose that electron and settle down into a more stable existence (a very unlikely outcome given their propensity to getting over-excited). The following animation shows a copper atom, with only one electron in its outer shell. The nucleus, comprised of 39 neutrons and 39 protons is shown as a single sphere at the center (To be honest, I didn’t feel like modeling all 78 spheres in the nucleus; my obsessive nature does have its limits).

Atom Model Moving - 25fps 640x480
Copper (CU),  Animation © DFD Architects, Inc.
At the risk of perpetuating stereotypes, we can group elements and materials by how they behave when excited. In terms of electricity, elements and materials (combinations of elements) can be put into three groups:

Conductors, Insulators and Semi-conductors.

Elements with 3 or less electrons in their outer shells are generally conductors (although the exact number of electrons does not always determine which elements are the best conductors). Because they have lots of empty room in that outer orbit, they are less stable and more likely to lose their remaining electrons when bumped around (The bump theory is a commonly held explanation for how electrons are passed from one atom to another). Insulating materials such as wood, glass and rubber are combinations of elements that fill their outer shells by sharing their electrons with other elements. These materials are composed of elements such as Carbon, Oxygen, Nitrogen and Hydrogen. Alone these elements are not very stable, but combined they have found comfort and stability. Selective elements such as Silicon and Germanium are termed semi-conductors, and have 4 electrons in their outer shell. With a little encouragement these elements can be persuaded to lose an electron or two and become negatively charged. These materials have become indispensable in the development of solid-state circuitry and computers in general.

That bumping around of electrons in a conductor is precisely where the transfer of energy via electricity happens. Like billiard balls on a pool table, when the energy is introduced at one end (the player hitting the cue ball), energy is transferred from one ball to the next. Not all energy is passed from one ball to the next however. In billiards, you’d hear the sound of balls hitting, and if measured, you could see the heat generated by the instantaneous collision. With electrons in a conductor, that energy release may be heat, light and almost always a magnetic field.

Magnets? I thought we were discussing electricity?

Everyone has played with magnets as a kid (or adult). Those of us old enough to remember iron filing and magnet toys such as “Wooly Willy”, have seen what a magnetic field actually looks like. The following image shows a magnet with a negative and positive end (or “pole”) often termed a North and South pole.  The iron filings align with the resultant magnetic lines of force (or ‘flux’). No we are not going to enter into a discussion of whether Santa Claus or penguins reside on either pole (maybe in a later post).

Patterns of magnetic flux (iron filings and a magnet)
Magnetic fields, created by electrons flowing through a conductive material, are precisely what enables a generator or alternator to initiate the flow of electricity, and appliances such as motors to use that flow of electromagnetic energy to create mechanical movement.

This whole discussion can seem very theoretical, given that we can only see the results of what magnetics and electricity can do. So how do we measure that flow of energy across a conductor?

Before we talk about measuring electricity, it’s important to know why it flows at all. Electromagnetic energy will not flow through anything unless it has somewhere to go. OK, time for a few metaphors:

Everyone is familiar with water pipes in their house, or at least knows that water comes from somewhere when the faucet is turned on. Why doesn’t water flow continuously from the kitchen faucet? It doesn’t flow all the time, because without an open outlet (someone using that water), it will just sit nice and quiet in the pipe. Open a faucet, and the water begins to flow. Break a pipe or create a leak, and water will flow to places you don’t want it to. Electricity is very similar. Without a load, or something to use that energy, there is no need for the electrons to bump into each other and pass along their energy. Unlike the water in our pipes however, electricity wants to flow from a positively charged source to negatively charged one (this is according to popular theory, but let’s leave theory out of this for the moment as it gives me a headache). More often than not, that flow may be from a positive terminal of battery to the negative one, or a positive source to the earth itself (such as in a building’s electrical system). Without a complete “circuit” to follow, the electrons will have nowhere to go, and the flow of electricity will stop. If you provide a complete path for the electricity to follow, then it will happily oblige. There is a reason that they refer to the Formula One race car events as a circuit. If the road was open on both ends and didn’t connect, it would be a very short race. Yes, I’m aware that would be considered drag racing; metaphors have their limits.

Measuring the energy carried by electricity

Before I lose anyone, let’s talk about volts, amps and watts. In my next post we’ll talk about AC/DC, and by that I’m referring to Alternating and Direct Current, not the 80’s band from Australia. I’m sure everyone has heard the phrase, “It’s not the voltage you have to worry about; it’s the amps”. While partially true; why? It has to do with force and potential energy.

If electricity is the flow of electrons, then measuring energy carried by electricity must involve electrons right? Well, unless you have an incredibly powerful microscope, and someone who is really fast at counting, we’re going to need a standard to measure against for counting electrons. Here we learn about Charles-Augustin de Coulomb, a French physicist whom the standard imperial measurement of charge was named after (his story would be another post). One coulomb is equivalent to the charge of 6.242 X 1018 electrons. That’s a lot of electrons. In obnoxiously large numeric terms, that’s six quintrillion, two hundred and forty-two quadrillion electrons. That should be easy enough to put into an Excel spreadsheet, right? Well, instead of counting every electron over a period of time, how about we just divide the total number of electrons by a nice big number like a coulomb? Well it so happens that the volume of one coulomb per second is referred to as an ampere. Whoa! Amps are actually related to something physical?! Don’t get too excited, we’re still talking about theoretically numbers and some basic assumptions, but at least we have somewhere to start.

So if one ampere (normally referred to as an Amp), is a volume of electrons over time, then we should be able to measure the energy those electrons are moving with them right? Not so fast. Volume (or size) is one side of the equation, but we’re missing the other half. We need a push. We need that potential energy to work with.

Caution: Dangerous metaphors ahead.

What is potential energy? If your house was on fire, and you asked for a water hose; I’m sure you’d be rather upset if someone walked up with a garden hose connected to a hand pump. You’d prefer a fire hose connected to a rather large fire truck I’m sure. Why? The difference is in potential energy. Only so much water can flow through a garden hose. Given a bigger and stronger hose, you could push more water through it. Water is normally measured in volume over time; commonly gallons per minute. A garden hose can easily provide 10 gallons per minute, but so can a fire hose. The fire hose however has the potential to provide much, much more water if it is needed (which it usually is). Here’s another example: Let’s say you are sitting quietly at the base of ten-foot cliff, and a rock is perched very precariously above you. It’s not moving, but given a bit of a push, it could fall at any time. If that rock weighed a few grams, the potential for harm to your pretty head is minimal. If that rock weighed 10,000 lbs., then the potential for harm would be rather substantial. Unless it’s actually falling, both rocks are harmless. The 5-ton rock however has a much larger potential energy (it COULD exert a much bigger force).

Since electricity transmits energy, we need to know the volume of energy over time, but we also need to know the level of force with which it is delivered. In terms of water in a pipe, this potential energy is referred to as pressure (in pounds per square inch, or PSI). In the flow of electrons, this potential energy or pressure is called voltage. One Volt is the potential energy it would take to drive one amp of current against a given load (we’ll talk about loads in the next post).

Now we’ve brought energy and force into the equation. Flowing electrons mean nothing if they bump off a conductor one at a time, but if they flow in great numbers (along with their accompanying magnetic fields) with a large amount of force, then now we have energy we can use. With both volume and force, we can move almost anything.

So how do we measure the power or work that electricity provides? Enter the “Watt”. One watt is equal to one volt of potential energy times one ampere of flow. The watt is a measure of the real power that pushes, heats or illuminates. For comparisons, this would be similar to horsepower (735.5 watts), or foot-pounds of force per second (1.355 watts).

In electrical terms, the watt, is proportionately equal to the volts (the potential energy) times the amps (the volume of flow). 1 Watt = 1 Volt x 1 Amp. I know. Some of you just went… uh, duh, but the majority of people just had that little 13 watt LED light bulb (equivalent to a 60 watt incandescent bulb) go off in their head and said, “Oohhhh, I get it.”. You’re welcome.

So let’s stop there for the moment, because unless you’re an electrical engineer or a geek like me, you may need a week to recover from reading this post.

Next time we’ll talk about Direct Current, Alternating Current, Single-Phase Power, Three-Phase Power, generators and transformers. I know, you’ll have a tough time waiting, but it should be worth it.

In the meantime, here is your moment of Zen (Yes, I’m a fan of the Daily Show on Comedy Central):



I promise not to beg, but I would really welcome any comments; both good and bad (but constructive). The more feedback I get; the better my posts can be. Thanks!!


The Money Pit, Copyright NBC Universal, 1986

A Christmas Story, Copyright Warner Bros. Home Entertainment, 1983

Magnet and Periodic Table images are public domain and are available on https://commons.wikimedia.org

Codes 101

Understanding the intricacies of building and life safety codes is simply a matter of learning why they exist, how they are used, and where to get started.

The codes and standards used to regulate the construction, maintenance and general use of nearly every structure in the United States can seem confusing, frustrating and even occasionally contrary to common sense. Like so many other aspects of modern life, specific skills and knowledge are needed when dealing with highly specialized subjects. It isn’t reasonable to expect everyone to amass the in-depth knowledge of biology, anatomy and chemistry needed to be a doctor; nor is it possible for everyone to have the skills and talent needed to compose, conduct or play the violin in a classical symphony. While music may require more talent than architecture and construction (in my opinion), they both require practice and a lot of learning. Understanding the intricacies of building and life safety codes is simply a matter of learning why they exist, how they are used, and where to get started. Although seemingly complex, once you have the basic concepts down, the code is something akin to the “Choose Your Own Adventure” book series produced by Bantam Books in the 1980’s and 1990’s. Given one set of decisions, the codes send you in a specific direction for requirements and additional choices to make. Maybe there was a reason I enjoyed those stories as a kid, because as a self-described Code Geek, I find it rewarding to track down code requirements and learn new things everyday (sometimes with negative results, but often with positive ones). Codes are critical to protecting the health, safety and welfare of the public through consistency and minimum levels of quality and protection. The codes were not created in a vacuum by politicians trying to increase tax revenue or regulate just for the sake of control. Every code and standard in use today began with individuals and groups getting together when agreed upon standards were needed; often in response to tragedies and failures that could have been avoided. The codes exist because of one reason; people caring for the safety of others.

What is a code, and who can enforce one?

The building and life safety codes today are published documents, rule books if you will, that provide guidance and limitations on a wide variety of topics and disciplines. The codes are generally written by both non-profit and private groups, and then published for use. The codes themselves are only words on paper until they are actually adopted by a jurisdiction that has the legal right to do so (such authority is typically given through federal, state, county or local government laws).

This is the single most important concept to understand: A code must be adopted by a governing body such as a federal, state, county, city or other such jurisdictional entity in order to be considered actual law.

Once adopted, that Authority Having Jurisdiction (AHJ), is now responsible for enforcing the provisions and requirements of the code. AHJ’s may also include taxing entities like water and utility districts, emergency service districts (fire and police services) and health departments. Once adopted, the code is the law of that jurisdiction and they are now responsible for not just enforcing it, but also the interpretation and even amending of it to suit their specific needs.

Most jurisdictions will also rename it to become their code. The City of Dallas, Texas, has adopted the 2015 edition of the International Building Code, and in doing so renamed it as the “Dallas Building Code”. (1) Technically under Texas state law, and many other states as well, a jurisdiction could write their own code from scratch so long as it meets the minimum safety standards as a published code. I’m not aware of any municipality willing to spend the time and money necessary to write their own code in lieu of starting with a nationally published one. In the end, although originally published by various organizations, those groups are not responsible for its enforcement, and do not have any authority to officially interpret the code; only the AHJ has that authority. Most AHJ’s will look to the original publisher for guidance, but it is the AHJ that makes any decisions needed. The key idea to remember is once adopted, it is their code.

An abbreviated history of US Life Safety Codes:

Prior to the 1890’s, no formal codes, standards or even guidelines existed to maintain consistency among the early pioneers and inventors of two burgeoning industries; Fire Sprinkler Systems and Electrical Systems. Following the invention and patenting of the first sprinkler head by Henry S. Parmelee of New Haven, Connecticut in 1874, and significant concerns surrounding electrical installations at the Chicago World’s fair and across the United States in 1893, interested groups began to meet and discuss the need for standards and rules for such systems. As expected, any early attempt at consolidating personal opinions and solutions would be unlikely, and at the end of 1895, there were five distinct electrical codes in the United States and no defined standards for sprinkler systems.

In 1896, and again in 1897, several national organizations met in New York in an attempt to consolidate the various standards, and in 1897, the “Joint Conference of Electrical and Allied Interests” established the “National Electrical Code of 1897” which was adopted and issued by the National Board of Fire Underwriters. This would eventually become NFPA 70, the National Electrical Code (NEC)

Also in 1896, a separate meeting was held in New York City by parties trying to consolidate standards for fire sprinklers; their release of sprinkler installation rules entitled, “Report of Committee on Automatic Sprinkler Protection” eventually became “NFPA 13”.

In November of 1896, a new organization known as the “National Fire Protection Association” (NFPA) was formed from many of the same members previously involved. The long history of NFPA and its members is a tribute to the thousands of individuals who have volunteered their time to establish rules and standards. (2)

The NFPA would then continue to play a large part in the development of new safety standards. As is the case with many codes, tragedies such as the Triangle Shirtwaist Fire on March 25, 1911 in which 147 people perished led to the development of the “Building Exits Code”, which would later become NFPA 101, The Life Safety Code. Although it existed at the time, the Building Exits Code was widely ignored, and further tragedies occurred such as the 1942 Cocoanut Grove Fire in Boston, Massachusetts in which 492 people died, and the 1958 fire at the Our Lady of Angels School in Chicago in which 90 students and 3 nuns died. Established criteria in the Building Exits Code prohibited the unsafe conditions in both buildings which led to the high loss of life. The Code was reorganized and renamed the Life Safety Code in 1966. Even with the codes existence, and attempts by the NFPA and other life safety professionals to affect public policy and concern, subsequent fires continued such as the 1977 Beverly Hills Supper Club in which 164 people died and the 2003 Station Nightclub fire in Rhode Island in which 100 concert attendees perished. Every tragedy has led to changes in the code, but in each case, significant loss of life could have been avoided if the rules of the code had been followed. (2)

What about the Building Codes?

As in any free society, many people with the same positive intentions cannot always agree, or for various geographical or societal reasons cannot centralize their ideas. Such is the history of building codes in the United States. Three major organizations published building codes beginning in 1927 (earlier editions did exist for one of the three in 1905).

The three major codes were:

The Basic / National Building Code (BBC), first published in 1950 by the Building Officials and Code Administrators (BOCA); used primarily in the Midwest and Northeast United States

The Uniform Building Code (UBC), first published in 1927 by the International Conference of Building Officials; used primarily in the Western states, and

The Standard Building Code (SBC), first published in 1945 by the Southern Building Code Congress International (SBCCI).

In 1994, the three model code organizations created the International Code Council (ICC) to create a single set of model codes that would provide uniformity across not only the United States, but to help facilitate international use and promote innovation worldwide regarding new testing, research and products.

The ICC published its first set of model codes in 2000, consisting of the International Building Code (IBC), Fire Code (IFC), Mechanical Code (IMC), Plumbing Code (IPC), and others. These model codes have since replaced the BBC, UBC and SBC nationally, and are even used outside of the US. (3)

So what is the difference between the Life Safety Codes and Building Codes?

Building codes strictly control the allowable size, number of stories, height and structural systems used in any new building. They deal with gravity, wind, earthquake, snow and rain loads. The building codes deal with materials and systems with regards to structural integrity, water intrusion, durability, energy efficiency, accessibility and myriad of other topics. They also include many of the same requirements as the Life Safety Code with regards to fire protection, egress systems, fire sprinkler and alarm systems, etc.

Life Safety Codes such as NFPA 101 do not dictate building size, structural requirements, overall building area, or initial permitting. The Life Safety Code is concerned with one thing; the safety of life. I know it sounds repetitive, but the Life Safety Code is concerned with protecting the occupants during a fire while they stay put, or protecting them long enough to evacuate from a building or structure. While the building codes also prioritize the safety of the occupants, the Life Safety Code focuses solely on that idea.

So why can’t we just use the building codes?

This is a subject of great contention amongst those who design and construct any building that may have more than one AHJ. I believe it comes down to jurisdictions not stepping on each other’s toes. I will use healthcare in the United States as the example, because it’s easier to explain and is the focus of my own career. Every nursing home in the United States that wishes to receive federal funds under the Social Securities Act (whose programs include Medicaid and Medicare), must meet the federal requirements administered by the Centers for Medicaid and Medicare Services (CMS). They must also be licensed by the state in which they are built. CMS is a federal agency, and therefore its rules must cover every situation that may arise in every state, county and city. While some people would not want a federal agency telling them how to build or maintain their facility, you can guarantee that if a fire occurred in a nursing home which received federal funding, someone is going to look at the government for answers as to why it wasn’t safer.

So, why not let the local AHJ handle that safety issue on their own? The simple answer is that it’s not always possible. There are millions of Americans who live in areas of the country that have no adopted building code or even a local government capable of adopting or enforcing one. Texas is a prime example, in that areas outside of a city’s jurisdiction are not required to have a building permit and county governments are only allowed (not required) to adopt fire codes and not building codes. Trust me, I was as shocked to learn that one as many of my readers will be.

Remember, that a code is just words on paper unless a governmental agency adopts and enforces it. If no local enforcement agency exists, then CMS in this case MUST have a set of standards to meet. You can imagine the disaster if CMS only enforced safety standards for some areas of the country and not others. CMS is also kept from enforcing a building code as, there again; imagine the issues with a federal agency issuing and granting permits, and inspecting all construction in the United States on every single project it funds (even indirectly). I don’t care what your political affiliation may be; that’s just not a good idea.

Keeping the building codes and Life Safety Code separate allows for various AHJ’s to protect their citizens, without overstepping their bounds (too much).

So where do you get started?

Sounds like a good idea for my next post; a basic primer on the IBC and Life Safety Code. If there are other general topics regarding codes you have questions on, please leave a comment.

References / Footnotes:

(1) City of Dallas, Texas, Building Inspection, Construction Codes


(2) History of NFPA, NFPA.org


(3) Building Codes, IMUA, 1998



All NFPA Standards, Cover Images and references are copyrighted by the National Fire Protection Association®, One Battery Park, Quincy, Massachusetts 02169-7471. All references and images reproduced above are for educational and reference purposes only.

The International Building Code® and all other similar codes referenced above are copyrighted works by the International Code Council, Inc., 4051 West Flossmoor Road, Country Club Hills, IL 60478. All references and images reproduced above are for educational and reference purposes only

Beware the ‘rule of thumb’

As the building and fire safety codes are based entirely on exact measurements, testing procedures and other such criteria, making any code related decision based on a hunch, or estimation would be rather unwise.

Image from http://s.hswstatic.com

All too often on the jobsite, I’ve heard the phrase, “Well, I was always told the rule of thumb is….”. You can fill in the blank as to what code requirement someone has distilled into an easy to understand and 9 times out of 10, incorrect assumption. So, what is a “rule of thumb”, and why should you be wary of following any simple “rule” as far as codes go? First let’s start with the concept, and then follow with some extremely common and incorrect rules of thumb”.

So what does the phrase “rule of thumb” mean?

Gary Martin, Author and Founder of www.phrases.org.uk provides the following meaning and history of the phrase:

Rule of Thumb: A means of estimation made according to a rough and ready practical rule, not based on science or exact measurement.


The phrase itself has been in circulation since the 1600s. The earliest known use of it in print appears in a sermon given by the English puritan James Durham and printed in Heaven Upon Earth, 1685, “many profest Christians are like to foolish builders, who build by guess, and by rule of thumb, (as we use to speak) and not by Square and Rule.”

The origin of the phrase remains unknown. It is likely that it refers to one of the numerous ways that thumbs have been used to estimate things – judging the alignment or distance of an object by holding the thumb in one’s eye-line, the temperature of brews of beer, measurement of an inch from the joint to the nail to the tip, or across the thumb, etc. The phrase joins the whole nine yards as one that probably derives from some form of measurement but which is unlikely ever to be definitively pinned down.

I like Martin’s definition, specifically the phrase, “not based on science or exact measurement”. As the building and fire safety codes are based entirely on exact measurements, testing procedures and other such criteria, making any code related decision based on a hunch, or estimation would be rather unwise. While it’s understandable that anyone in the construction (or design) fields may want to simplify the rationale for doing something to direct their teams, workers, or supervisors quickly, this often results in a very watered-down version of a specific code requirement. Given enough time, the “rule of thumb” passes through so many people that it doesn’t even resemble the original statement. If you have never played the “telephone” game in grade school, I encourage you to Google it.


Rule of Thumb No. 1, “Electrical boxes that are in different stud cavities do not need putty pads”.

This rule deals with the requirements for metallic or non-metallic (plastic) electrical boxes that are installed in a fire-resistive wall assembly. The mere mention of a “stud cavity” exists nowhere in the commonly used building codes or standards that exist in the United States today. The International Building Code (IBC) and NFPA 101, the Life Safety Code (LSC), both require protection of any penetrations in a rated assembly to prevent its failure. Electrical boxes are specifically required by NFPA 70, the National Electrical Code to be installed in accordance with their listing. So here is what that listing says (taken from UL’s Guide QCIT.GuideInfo, Metallic Outlet Boxes, on www.ul.com):

Listed single- and double-gang metallic outlet and switch boxes with metallic or nonmetallic cover plates may be used in bearing and nonbearing wood stud and steel stud walls with ratings not exceeding 2 hr. These walls have gypsum wallboard facings similar to those shown in Design Nos. U301, U411 and U425, as covered under Fire Resistance Ratings – ANSI/UL 263 (BXUV). The boxes are intended to be fastened to the studs with the openings in the wallboard facing cut so that the clearance between the boxes and the wallboard does not exceed 1/8 in. The boxes are intended to be installed so that the surface area of individual boxes does not exceed 16 sq in, and the aggregate surface area of the boxes does not exceed 100 sq in per 100 sq ft of wall surface.

Boxes located on opposite sides of walls or partitions are intended to be separated by a minimum horizontal distance of 24 in. This minimum separation distance between the boxes may be reduced when Wall Opening Protective Materials (QCSN) are installed according to the requirements of their Classification.

The boxes are not intended to be installed on opposite sides of walls or partitions of staggered stud construction unless Wall Opening Protective Materials (QCSN) are installed with the boxes in accordance with Classification requirements for the protective materials.

You’ll notice very quickly that the words “stud cavity” do not appear in UL’s listing for Metallic Outlet Boxes, and to my knowledge do not appear in any other code, standard or listing. The 24” horizontal separation for boxes on opposite sides would definitely correlate to a wall built with studs at 24” centers, but it’s only a coincidence. In this case, the “rule of thumb” is 100% incorrect.

Rule of Thumb No. 2, “No storage is permitted anywhere within 18” of the ceiling in a building protected by sprinklers”.

This rule is simply a misunderstanding of the code requirements surrounding possible obstruction to the flow of water from a sprinkler head when activated. In this particular case, keeping all storage at least 18” away from the ceiling would definitely help in avoiding sprinkler obstructions, but when the same rule of thumb is used in reverse (to cite violations of the code), it would be very wrong.

NFPA 13, the Standard for the Installation of Sprinkler Systems, 2010 edition, states the following for standard upright and suspended (pendant) sprinkler heads:

NFPA 13, § Obstructions to Sprinkler Discharge Pattern Development Continuous or noncontinuous obstructions less than or equal to 18 in. (457 mm) below the sprinkler deflector that prevent the pattern from fully developing shall comply with

The following figures and charts from NFPA 13 show the required distances from any obstruction to the sprinkler head.

You’ll notice that obstructions less than 24” in depth are permitted when up against the wall of a room protected by a sprinkler (as depicted). This means that storage is permitted within 18” of the ceiling, but only in accordance with this section. Is it safer to just keep everything 18” below the ceiling? Yeah, it probably is, but spreading that requirement as a “rule” that uninformed people use as a “requirement”, only leads to confusion and conflict later (especially when used as a justification by inspectors).

What to do when everything you were told is wrong:

So I may have burst your bubble on two rules of thumb that are really not correct; what other rules of thumb are out there that could be wrong? I’d love to know. With some research, patience and willingness to challenge your past experience, we could eliminate those estimations and guesses; replacing them with the (sometimes simple) truth.

If you have some examples to share, or would love me to weigh in on, please write them in a comment. The more we discuss about what is actually correct or required the better off we all are.

Sources and Copyrights:

Excerpts from UL Guide QCIT.GuideInfo are reprinted from the Online Certifications Directory with permission from UL, © 2017 UL LLC

NFPA 13 and NFPA 101 are copyrighted by the National Fire Protection Association, and reproduced here for reference and educational purposes only


Codes must be followed to be effective; Immediate lessons from the Grenfell Tower tragedy.

Photo from https://static.dezeen.com/

A huge amount of information has flooded the internet and media outlets regarding the possible causes and now future ramifications of this tragedy. As the exterior cladding of the building is being initially blamed for the fire’s rapid propagation, the presence of such a material on dozens of other government owned housing blocks has led to large-scale evacuations of residents, putting thousands of people out of their homes.

This fire will no doubt lead to civic and criminal investigations in the UK, but what can those of us in the United States learn from such a disaster? The worst possible outcome for those of us watching from across the Atlantic would be complacency, “Oh, that wouldn’t happen here.” Really? Are you sure?

What went wrong?

Initial investigations by local authorities and news organizations has focused on a “flammable” exterior cladding installed during a recent renovation project to the Grenfell tower and others like it. The product installed (allegedly confirmed by the manufacturer) was a Metal Composite Material (MCM) as defined by the International Building Code (IBC), a model code that has been adopted in some form across all fifty states in the US. The MCM installed on Grenfell Tower is a product called Reynobond PE, manufactured by Alcoa Architectural Products, located in Eastman, Georgia. Reynobond PE consists of layers of Aluminum sheets over a polyethylene core (foamed plastic). The panel as a whole meets IBC flame spread requirements (Class A per ASTM E84), however the polyethylene core on its own does not. The product is manufactured in accordance with US standards and is permitted for installation on buildings as high as 75 feet tall per the IBC, with VERY specific exceptions. The primary exception is that such a product cannot be installed on a building higher than 40 feet above the ground unless that building is equipped with an automatic sprinkler system, and then never installed above 75 feet above the ground. Alcoa also produces a product called Reynobond FR, which has a mineral board core that meets the ASTM E84 flame spread requirements on its own.

Another likely cause of the fast growing fire was the way in which exterior columns were clad in MCM panels. Quickly looking at the plans of the Grenfell Tower, listening to reports and interviews of tenants, and reviewing images of the devastation itself, one can quickly see several problems that possibly led to the fire’s growth and more importantly made it extremely difficult to for residents to escape the building before conditions became untenable.

Photo from: https://cdn.saleminteractivemedia.com

Grenfell Plan

  • There appears to be a relatively large gap between the cladding material and the structural columns of the building itself along the exterior. This kind of cladding style is called a “curtain-wall”, as it is attached to the face of the building, and does not terminate at each floor, but creates its own cavity on the building’s perimeter. looking at the pictures following the fire, the space between the structural column and the cladding is quite large. Per the IBC, this kind of curtain wall assembly must be
    Grenfell Colored Elevation.jpg
    Images from : http://i.dailymail.co.uk

    firestopped at each floor level using a Perimeter-Fire-Containment System such as those tested and listed in the UL Certifications Directory (systems such as CW-D-1001).

  • Grenfell Tower had only a single exit stairway. For a 24 story residential high-rise, which would have an occupant load of no less than 22 people per floor (based on the floor plan of Grenfell Tower and the 2003 IBC), a minimum of 2 stairways would be required without exception.
  • The building did not appear to have an automatic sprinkler system or manual fire alarm system interconnected with automatic detection devices.

All of these factors likely contributed to the fire’s rapid growth and the inability for residents to evacuate fast enough.

Codes have to be followed to be effective:

You may say then, “Well, those issues can’t happen here because our codes don’t allow it”. This is where the truth really matters. It can happen here. Having the rules to follow doesn’t mean that everyone follows them. Having laws that limit the speed on every highway in America does not keep thousands of people from breaking them every day. I could not begin to list all of the code violations I have witnessed over my career that were either simple mistakes, intentional omissions, or a lack of understanding about what the code really requires. The third reason is actually the scariest one. Honest mistakes happen, and I’m sure intentional code violations exist as well, but in my experience, the most common reason codes are not followed, is because designers, owners and contractors don’t understand them. Ignorance is not bliss, its dangerous.

Although I have not seen a building constructed with too few stairways, I have seen plenty of stairs that were not protected from the rest of the building, had blocked exit doors at the bottom, were too narrow, had locked doors going into them, or some other issue that essentially eliminated them as a possible exit. Having the stair doesn’t mean anything if you can’t use it.

Having a fire alarm and fire sprinkler system is absolutely worthless if the systems are not installed correctly and then routinely inspected and maintained to ensure they work. Having a sprinkler system means nothing when it fails to work because someone unintentionally blocked a sprinkler head or closed a valve.

The exterior columns at Grenfell Tower, if it does turn out to be the issue it appears to be, is due to a lack of understanding on how a fire acts, and why the building codes are written to limit the spread of a fire. This exact issue could happen in the US if a contractor substitutes a less-expensive product (like the Reynobond PE instead of using the FR version), having no other intention than saving the owner money, but the design team is either not part of that decision, or fails to understand its ramifications. Whether the PE or FR product was used, a building official in the US could easily miss the requirements to firestop the perimeter of each floor at such a system. Such omissions could result in a similar fire without anyone even knowing the issue exists.

What can you do?

Educate yourself. Surround yourself with educated people if you can’t understand the requirements yourself. The costs are too great to downplay or ignore anything having to do with fire safety and building codes in any type of construction.

Ignorance is not funny and not acceptable. Education and knowledge are our greatest asset in preventing tragedies such as the Grenfell Tower fire from happening again.





Notice: The commentary above regarding possible causes and circumstances surrounding the fire at Grenfell Tower are personal speculations and assumptions. Educate yourself on the facts. Listen to the evidence presented to you and research the actual laws and codes that were applicable. That’s my entire point.