How-To: Electrical Safety
Overview/Caution: If you have never fixed an extension cord, replaced a plug on a lamp or a wall switch in you home, then you should not attempt to do much of your own Christmas light wiring until you have at least read some how-to booklets from your local home building supply store. Christmas lighting involves using electrical voltages that are lethal and can easily kill you. Electricity is very, very fast. Electricity is not forgiving at all. You may only get one chance to do it right because if you do it wrong, well, good night Irene.
This section is not a treatise in all possible electrical safety issues. It does provide a basic guide to common situations that occur to DIY'ers who dabble with Christmas light displays.
Main Power Panel: this is located in your house somewhere, and it's where the main power from the outside connects to the circuit breakers or fuses in your house, and where the main power is distributed into multiple other circuits that go throughout your house. Unless you have an electrician's certification, the only thing you should be doing in the main power panel is switch existing circuit breakers on or off, or replace fuses if you use them instead. Hire a licensed electrician to add or change anything inside the main power panel. While you can get a really big shock from a regular outlet in your house and you may survive it, the main power panel carries enough power that you can get fried.
Circuit breakers/fuses: if a circuit breaker trips off and you go to reset it but it trips off immediately again, DO NOT KEEP TRYING TO RESET IT! Some homeowners just "push it harder" or "hold it in there" to try to make it stay. A circuit breaker trips for your protection, and it means that something has shorted-out the wiring on that circuit. Continued application of power to the circuit could easily result in a fire. The same goes for a fuse: if you screw in a new fuse and it blows immediately, you've got a serious problem that a new fuse cannot possibly fix. Leave the circuit off and call a licensed electrician for help.
Grounded Plugs vs Polarized Plugs: Most DIY'ers use a mix of grounded (3-prong) plugs and standard, extension cord type polarized plugs, which have only two connectors. On a polarized plug, one of them is a bit wider than the other and the plug only fits into a socket one way. The wider connector is the "neutral" part of the circuit while the narrower connector is the "hot" one. A 3-prong grounded plug also usually has polarized blades, too, but the round, ground pin that connects back to the earth/ground ensures that the plug fits into the socket only one way. While we won't cover the nuances of whether you should always use one type or the other, consider that Christmas lights generally have only two-prong plugs yet they're designed for both indoor and outdoor use. And, in fact, they are safe to use almost anywhere as long as you follow the maximum current guidelines, e.g. how many light strings may be plugged into one another. If the light strings say no more than 3 strings can be plugged end-to-end, don't push it and go for that 4th string. It may work, but you're playing with fire (maybe literally!) as the extra electrical load on those small wires may heat them up, melt the plastic insulation and result in a fire. The guidelines are there for your safety. Heed them.
GFCI - Ground Fault Circuit Interrupter: You probably already have one or two GFCI outlets in your house. They're generally located in a bathroom, laundry, basement or garage, but they're the wall outlets with the little "test" button that when you push it, another button "snaps" and pops out, shutting off the electricity. A GFCI outlet is there for your protection, and if it pops often, it indicates that you have some sort of electrical problem somewhere on the circuit that outlet is on. A GFCI is not the same as the circuit breaker or fuse in your main power panel. A circuit breaker pops open when there's either a direct short or the circuit is overloaded with too many electrical devices that are using more electricity than the wires are designed to safely carry. A GFCI works differently as it actually measures whether there's a voltage difference between the "hot" and "neutral" wires on the circuit and if there is, it pops and cuts off the power because there's not supposed to be. For example, let's say you have a connector in the yard that's gotten wet and is leaking a little bit of electricity onto the lawn -- a severe hazard for anyone walking in the yard because it could result in a potentially lethal shock. A GFCI would sense the leak and would cut the power to the circuit. A circuit breaker isn't that sensitive.
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