Thanks to everyone that participated in our "After the Storm" quiz last week. Can you guess which question stumped the most people? If you said the question about generators, then you'd be right. So this week I'd like to follow-up with an article written by our own Development Services director, Tom Hosey, on the subject of portable generator safety.

Some time ago, while Tom was in Houston and serving on the board of directors for the Building Officials Association  of Texas (BOAT), he wrote the following article for the BOAT newsletter. It has been modified just a little so that it is applicable to our state. While the article is longer than our typical blog post, it is full of great information and worth the read. Enjoy!  

Portable Generators and Safety, by Tom Hosey

Hurricanes, floods, tornadoes, hail, wind, and ice storms are not uncommon occurrences here in the Tar Heel State. Unfortunately, to make matters worse, when these incidents occur they often result in temporary electrical power outages. Some homeowners will often attempt to utilize portable generators to provide power for their critical needs such as refrigerators, freezers, water pumps, and lighting.

Relatively inexpensive portable generators can be a great alternative approach to costly, permanently installed systems and are very capable of supplying most of these basic critical needs. However, if these portable generators are not interconnected to the electrical system in a safe code compliant manner, they create a number of extremely dangerous conditions to the homeowner, their electrical system, and potentially the electrical utility workers who may be trying to restore power to the house.

The easiest and intrinsically safest approach is to simply run the portable generator in a well-ventilated area, using extension cords to connect appliances, pumps, and other devices that you want to be able to use directly. However, this approach may not be the most convenient as it requires multiple extension cords to be rolled out through the house, hard to reach equipment moved to connect it, and does not allow the use of any fixed appliances without a cord and plug hookup (such as an electric water heater).

In an effort to avoid these problems, some homeowners will attempt to back feed the generator into the electrical system by using modified extension cords, plugging the generator into a house receptacle (a 220 volt dryer receptacle, for example), and turning the main electrical circuit breaker off. While this will energize and restore electricity, it is a violation of the National Electrical Code (NEC) and is very dangerous if the main circuit breaker is not turned off. If the main circuit breaker is not in the open (turned off) position, power is back fed by the generator through the main circuit breaker to the utility step down transformer. This can cause the transformer to act as a step up transformer and energize, with a high current in lines that should not be energized (dead), shocking or killing a utility worker who is trying to repair them. In addition, when the utility power is restored not only will this pose a hazard to the owner and his family, but the back fed generator will likely burn up and the house wiring and connected equipment could be damaged, and create a fire hazard. For these reasons the NEC prohibits this type of installation and generally requires the use of a transfer switch.

Transfer switches isolate the utility power from the generator and typically require you to identify which circuits you wish to utilize for emergency power, then relocates these circuits and installs a new dedicated emergency electrical panel or combination transfer panel. The cost of this type of installation is substantial and can be prohibitive. There is another safe, code compliant, far less expensive, and quicker method with the use of a simple interlock device (NEC article 702). When the interlock device is installed on the existing electrical panel there is no need to install any new panels or relocate any existing circuits. In addition to the interlock device, you will need to install one new emergency generator circuit which can be plugged into the generator.

All of the new components need to be listed, installed per the requirements of the NEC, and of course, permits and inspections obtained from the local authority having jurisdiction, to insure the installation was performed safely. These interlocking devices (listed to UL 67) utilize a sliding mechanism which is attached to the outside of the panel that prevents the new generator emergency power circuit breaker from being closed (turned on) unless the main circuit breaker is opened (turned off) first. You will still need to utilize a generator with sufficient watts capacity to provide the load you plan on running and follow all normal safety precautions, manufacture's recommendations and limit the load to the generator's capacity.

A little background on these devices, in the Houston Texas area these simple interlocking devices first came about as a response to Hurricane Katrina. They were a safe, quick, and inexpensive method that allowed electrical panels to be energized by vehicle mounted or portable generators where existing emergency power provision was needed but did not exist. A prime example of this was at service gas stations that had gasoline in their underground tanks, but no onsite emergency generators or provisions to safely interconnect portable generators. When emergencies happen, and power goes out, a portable generator can be a valuable asset to have. However, unless you want to simply use extension cords, a safe method to interconnect to your house electrical system needs to already be in place. If your need is infrequent a simple interlock system might be the best option for you.

Thomas J. Hosey, CBO, CASp

Director Development Services

Raleigh N.C.

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