Extension Cords
One of the biggest reasons for the popularity of cordless electric tools has to be the extension cord. Sure, extension cords get power where you need it, but along the way, they can cause a variety of problems. They can snag, hang up and unplug, just as you reach the top of a ladder. Undersized cords can cause voltage drops, reducing the power of your tools, making them overheat.
Those same cords can cause blown fuses, tripped breakers, fires and electric shock. All these problems are preventable, however, if you use the right cords – and use them right.
The right cord: For an extension cord to perform properly, first and foremost it must have conductors large enough to carry the current being used without overheating. Electrical wire is sized according to a number system called AWG (American Wire Gauge). Just to make things interesting, this system bucks common sense. The higher the number, the smaller the wire.
The minimum wire size for any job is determined by the amperage of the tool being used and the length of the cord. Thus, a big 10-amp tool will require a heavier cord than a tool that draws just two amps. And a 150-foot cord should be heavier than a six-footer.
Whenever you buy a cord, make sure it is heavy enough to handle the job you have in mind. If in doubt, go oversize.
A cord can never be too heavy, but a cord that’s too light can cause problems. To make sure you get the right cord, check the specification plates on all the tools or appliances you might ever plan to use with the cord. Look for the amp ratings. Then look for a cord heavy enough to handle the highest rated tool.
Ready-made cords are generally packaged with labeling to help you make the right decision. This information may come in the form of a chart, or the cord may be labeled showing its maximum amp rating. If you have old, unrated cords around the house, look for the AWG printed on the wire. Then use the following information as a guide:
For cords 50 feet and under, 18-gauge wire will handle up to 10 amps. If the cord has 16-gauge wires, it can handle 13 amps, and 14-gauge wire can handle as much as 18 amps.
Hundred-foot cords will have to be heavier. In this length, 18-gauge wire will take only as much as five amps, 16-gauge will take only 12 amps and 14-gauge will take 17 amps.
Once you get a cord, it’s not a bad idea to label it with its maximum amp rating so you won’t forget it between jobs.
Wire size is your primary consideration, but it’s not the only one. Wire type is also important. The most common wire for cords is called SJT. This is a round wire, with a tough plastic jacket for abrasion resistance. A cheaper type, the flat, two-wire cord common on lamps, is called SP or SPT. This is OK for short, light-duty cords, but it won’t hold up well in tough applications where wear might be a problem.
Two or three conductors? Three-wire cords – the kind with the three-prong plugs – are safest. You’ll need this type with many tools and appliances anyway, because most have three-prong plugs themselves.
Specialty cords: If you will be using a cord that will be dragged around a lot – powering an electric mower, for example – get the kind with special interlocking plugs. These won’t pull apart just when you need them. If you have problems with tools pulling out of cords you already have, make a simple knot like the one shown in the accompanying sketch.
If you have air conditioners or an electric range, you’ll probably need special cords. These high-amp appliances have unusually configured plugs designed specifically to keep you from using them with ordinary cords. Only heavy-duty cords with matching plugs and connectors will do the job.
So before you go buy a cord for one of these appliances, make a little sketch of the appliance plug showing the shape and orientation of the prongs in the plug. Take the sketch along when you go shopping.
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