We know how the electric generator works, what it can and can’t do, and what type of loads it can handle, but we still need to get the power to the tools. This requires extension cords. They are one of the most misused tools on the fireground.
VOLTAGE DROP AND EXTENSION CORDS
The National Electric Code (NEC 400.5 (A) (B) states that 3% is considered the maximum voltage drop using flexible cables/extension cords we can tolerate without sacrificing performance. About 4 volts is 3% for a 120 VAC circuit. 120 VAC x 0.03 = 3.6 VAC. So, the minimum operating voltage we should allow is 116 VAC at the end of our cord, working the tool. Extension cord size, both length and gauge, is a part of delivering amps and volts the tool needs to work at peak efficiency. This needs to be measured while the tool is operating.
A 12-gauge, 3-wire extension cord powering an appliance 100 feet away from the generator and drawing 20 amps will lose more than 6 volts in friction loss, or electrical resistance. If we increase the length of the extension cord, we also increase the resistance to the amperage flow and increase voltage drop. The same can happen if we use a smaller diameter wire.
If you are using electric cord reels on your fire apparatus, consider this: Your 100- to 200-foot reel may seem quick and convenient, but at what price? Using a reel, even if you are only 25 feet away, you are still using the entire length of the cord on the reel and living with all the losses with the length.
How far is your typical extension cord stretch? Anything more than 100 feet needs to be 12 gauge at a minimum and, if you are running anything bigger than a reciprocating saw with a 12- to 15-amp load, it should be 10 gauge. You should consider parking closer or using a portable generator and moving the power source closer to the work.
A coiled extension cord can only carry a full-rated current load when completely unwound off a reel. The cords are rated when exposed to air for cooling to dissipate the heat buildup through either long-term use and continuous buildup or coming to full load, as either condition can damage the cord and lead to shock or fire. Coiled cords are not efficient.
COILED/REEL EXTENSION CORD DAMAGE
The bottom line is this: At a minimum, you should have two 50-foot cords, one that’s 12-gauge and 25 feet long and a second 50-foot, 10-gauge cord. These will handle most of your needs. If you need a long stretch, start with a 10-gauge; add the 12-gauge from there. It’s just like using a 2½-inch hose to extend a 1¾-inch handline.
Keep generators portable and understand the losses in electrical power transmission. Also, keep in mind that just because there is a big four-outlet junction box on the end of your cord, this does not mean you can plug four big electrical loads into it. You need to know your power requirements for all your tools, including startup current.
If you are living with cord reels, which often contain 100 feet or more of cord, measure the voltage to make sure you start out at 120 VAC; if not, repair as needed. Then, keep in mind the friction losses/voltage drop considerations. Even if you have a large apparatus-mounted and driven generator, a 20-amp 120-VAC outlet can only deliver ratings consistent with the friction loss chart. The losses will occur no matter the size of the generator.
If you are using “pigtail” adapters that convert a twist lock plug into a straight blade outlet, these can add an additional voltage drop into your portable electrical distribution system. When possible, eliminate these adapters. Check with tool manufacturers to see if changing the straight blade male plug into a twist lock would void any warranties. Some tool dealers have no issue with that kind of change and, if you have no warranty left on your tools, replace the plug and eliminate the pigtail adapter for better overall performance.
The extension cord covering also has a rating. Your cord should have letters stamped into it indicating the rating and application of the cord. For example, “S” cable is rated for severe or rough service. An “O” indicates an oil resistance jacket, and “OO” represents an oil resistant inner and outer jacket. “HH” is rated for high heat. A “W-A” cord is weather resistant. These are just a some of the ratings you will likely encounter; there are many others. Ratings can be combined—for example, most fire departments should use 10- or 12-gauge SOOW cable, rough service, resistance to oils and water.
GROUND FAULT CIRCUIT INTERRUPTER USE
A ground fault circuit interrupter (GFCI) is a device that shuts off electric power when it detects that current is flowing along an unintended path, such as through water or a person. A GFCI is used to reduce the risk of electric shock, which can cause the heart to stop or cause burns. It can also prevent fires, such as when a live wire touches a metal conduit, preventing the conduit from heating up. It is to be used when operating electrical devices around water or in a damp place.
When using a portable GFCI, try to keep it with the operator/tool, not at the power source, so there is less time spent walking back and forth if it trips.
A GFCI works by measuring the current leaving one side of a power source, the so-called live or hot wire, and comparing it to current returning on the neutral side. If they are not equal, then some of the current must be leaking in an unwanted way, and the GFCI shuts the power off. After the problem is fixed, the device must be reset manually by pushing the reset button. If the problem is not fixed, the GFCI will keep shutting off. There is also a test button next to the reset button, which allows you to confirm that the GFCI works properly.
NUISANCE GFCI TRIPPING
It takes a small current leakage of only 5 mA (0.005 A) from the hot wire to the ground or neutral to cause a GFCI to trip. A small amount of leakage current may be difficult to avoid in some normal circuits. Hand-held power tools do not cause a tripping problem if the tool is maintained in good condition. Some stationary motors, or fluorescent lighting fixtures, may produce enough leakage to cause nuisance tripping. Another issue could be multiple extension cords connected and if the connections are damp. A damaged outer sheath of the extension cord could allow water in to cause enough current leakage.
To avoid nuisance tripping, a GFCI should not supply worn cords with cracked insulation, soft electrical grounds created by dampness or dust, or extension cords more than 100 feet. Do not automatically dismiss these trips as a nuisance. They may very well be a clue that there is a malfunction, so take the time to troubleshoot the issue. Keep in mind a circuit breaker feeding a GFCI will not trip open on a ground fault. Additionally, a GFCI won’t trip in an overcurrent condition.
Check the electrical connections, as someone may have put a tool away wet. Keep dewatering aerosols in your toolbox that can be used on electrical tools and take note that some generators have a built-in GFCI on all outlets.
Take a few minutes and measure your electrical outlets; confirm that you are really starting out with 120 VAC. Don’t take it for granted. Figure out your electrical loads, and measure your voltage drops to make sure you are getting the most out of your tools.
STEVE SHUPERT has 37 years of public service. He retired from Miami Valley Fire District in Montgomery County, Ohio, and serves as a rescue team manager for Ohio Task Force #1 Federal Urban Search and Rescue. Shupert is also the chair of the FEMA Rescue Sub Group and the director of training for 501c3 Crash Course Village in Kettering, Ohio.
