Commercial Construction Considerations: Electrical Systems

This article discusses some of the components of electrical systems that you will find in commercial facilities.


In the past few articles, we have looked into several different building components including structure, HVAC, roofs, in addition to performance based design. One important building component that we have not discussed is the electrical system. This article will take a look at building electrical systems. We will also discuss some of the basics of utility electrical systems, but that topic is very important and is outside of the scope of this discussion.

Why is knowledge of a buildings electrical system important? The most vital is life safety. Coming into contact with the wrong components of the electrical system in the buildings where we fight fires, perform rescues, or provide EMS could lead to severe burns, and death. Most of the time these deaths can be easily avoided if we had a little more knowledge, paid a little more attention to what we were doing, or didn't try to get just a little bit closer to that power line.

The easiest way to discuss this topic is to start at the utility pole on the street. They are typically transmitting high voltage, from 4.5 to 13.2 kilovolts. This power is then transformed to one of several lower voltages for use in commercial buildings and homes.

Most commercial buildings use, 120/208 volt power or 277/480 volt power, while most homes use 120/240 volt power. The actual voltage that a facility uses is not overly important. However, it is a good piece of information to have.

The Basics
The transformers that convert the voltage are located in several places including utility poles, mounted on pads, or in some cases -- mostly in older facilities -- you can find them in the basement of a facility. These are very dangerous to personnel who are not adequately trained. Firefighting personnel should never open a pad-mounted transformer and should never use an aerial device to gain access to a pole-mounted transformer.

In addition to the electrical hazards, most transformers contain oil to assist in the cooling process. This oil should be treated as we would treat any other hazardous material. In addition to the cooling oil that is used today, you may still find polychlorinated biphenyls, or PCBs used as the cooling fluid in some older transformers.

These transformers should be clearly labeled which is why we need to remember to take a minute and think about what we are doing before we do it. As with any Class C fire, a transformer fire should be handled with a dry chemical extinguisher that is rated for Class C fires. When fighting these fires make sure you know what you are dispensing the dry chemical on. If the cooling oil is exposed, you will splash it, spreading the fire.

Once the power from the utility is transformed it then comes into the building or to the side of the building, where it is metered. This typically happens outside the building and then the power is routed to the main control point for the power.

The Main Control Panel
The device used as the main control point can be referred to by several different terms including, main disconnect, main circuit breaker, or main switchgear. Regardless of what it is called, this is the point in the system where the power to the entire building can be shut off. You should not assume that it will turn all of the power off. The only way to be sure that the power to the facility is completely off is to have the electric company disconnect the conductors feeding the facility. From the main switchgear, the power system continues to out to sub panels located throughout the facility, and from the sub panels to actual devices, lights and receptacles.

There are several items that you need to be aware of in the electrical room including the switchgear described above, conduits, transformers, and wire ways. Firefighters need to be very careful when operating in electrical rooms because of water use with exposed panels and exposed conduit. Many electrical rooms in commercial facilities are located in the basement or in a room below grade.

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