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Ideas from Ed: Finding accord (actually, a cord!) (Volume 7, Issue 4)

Sooner or later, every homeowner faces the task of replacing the electrical cord on a tool, appliance, or other powered device.  It really should be a straightforward task, but let’s go over some of the basics so that you do it safely and the repair lasts for a long time.

 

Cords become unsafe from a variety of issues, including exposure to sunlight, abrasion, and repeated bending.  Replacing them before they become brittle or lose any insulating cover will prevent a short circuit and possibly shock or even electrocution.  So what items are important when selecting a replacement?


Let’s begin with the size of the wiring in the cord.  All modern cords are stamped or printed with the “gauge” of the wires within them.  Typical numbers would be something like 18 AWG (American Wire Gauge) on a wire for a small lamp, 16 AWG for a vacuum cleaner wire, and maybe 14 AWG for a power saw.  The numbers are generally “even” and as you can easily infer, the smaller the number, the larger the capacity of the wire.  It’s OK to replace an 18 gauge wire with a 16, but not the reverse.  For an appliance that does not need a lot of power to operate, the manufacturer uses smaller wire not only for cost-savings, but also to make the wire more flexible.  (Think of that $2 extension cord you bought, and how it’s all folded up for packaging…)  When installed on an item where the current draw is greater, having a wire of suitable dimension (larger) will allow the current to pass through the wire without generating excessive heat.  The number of conductors is also shown on the wire, so 18AWG/2 would be 18 gauge wires of 2 conductors (no ground).


Next, let’s look at the material the wire is made from and the type of insulation.  Again, these can generally be read from markings on the original wire.  What you’re most likely to find on the majority of items will be  SPT-1 or SPT-2.  SPT stands for “stranded parallel thermoplastic” and the numbers 1-3 indicate the relative amount of insulation over the copper conductors within.  SPT-1 has the least amount of insulation, making the wire very flexible but less suited where abrasion (for example) might occur.  SPT-2 is still flexible, but noticeably stiffer than SPT-1, and less so than SPT-3.  You might also find additional information on the original wire, perhaps wording like “HEATER” which would indicate the wire’s particular suitability for use on something like a space heater.  In all cases, the goal is to replace the original wire with a replacement that is just as well suited to the appliance’s use.

 

Along with the wire, you would likely need to replace the plug on the end.  By far the easiest and best way to accomplish both is to buy an extension cord or a replacement power cord that has the plug already attached.  I have found it way less expensive to simply buy an extension cord and cut/discard the outlet end than to buy wire and a replacement plug.

 

If you must replace the plug, your hardware store will have a myriad of choices of styles, colors, and capacity.  Some are easier to install on wires than others.  You must never replace a plug with the 3rd grounding prong with one that does not have one, though!  The packaging will indicate the capacity in amperage, so make sure it’s matched to the capacity of the wire.  Here’s an example of a plug designed to fit onto round wire for something like a power tool:


It’s important that when attached, the plug-to-cord connection and the cord-to-appliance connection are such that normal usage does not strain the connections.  One way is to tie the wire ends into the “Underwriter’s knot” if the knot can be housed inside the appliance or plug.  Doing so will prevent the wire ends from pulling out from their connections if the wire is tugged on.  Here’s the Underwriter’s knot:

You can also purchase snap-in cable clamps which secure the wiring in place.  Better yet, if the original appliance wiring has such a clamp, pop it out and re-use it.  Here’s an example:




There’s also one more thing that’s really important, and you may need to think about this before taking the original appliance cord off.  That’s polarity.  Although most appliances will “work” if wired in reverse, they will not be safe.  The power should go from the outlet/plug through the wire to the appliance switch, then through the appliance back to the plug and into the outlet.  The “backwards” way has power going from the plug through the wire and through the appliance, then through the switch and wiring back to the plug and outlet.  Note in the second case that the appliance is “full” of electricity even when the switch is in the off position!  Modern plugs have one prong that is wider than the other, meaning that it must be oriented correctly in order to fit into a modern outlet.  Outlets have corresponding receiving slots so that the plug can only be inserted one way.  See this picture of the different sized prongs on this plug:

Assuming that your outlet is wired correctly (and you can check this with an inexpensive plug-in device available most anywhere) the power comes out of the outlet at the smaller slot, and into the plug with the smaller prong.  That means that the wire attached to the plug’s smaller prong needs to be the one that attaches to the appliance switch.  In order to assure that you can trace the electrical path along the wire, 2-conductor wires have some type of marking to differentiate one side from the other.  Look carefully at this wire pair, and you will see that one wire has smooth insulation, while the other has a linear feature.  Since the smooth one connects to the smaller plug prong, that smooth wire must be the one attached to the switch.  You can also use the writing or imprinting on a wire pair to follow them as well.  Tracing the path of the original appliance wiring from the smaller plug prong to its attachment point will assure that you can attach a new wire and plug the same way.



Plugs for 3 conductor wire don’t need to have one prong wider than the other, since with a grounding prong, the plug can only fit into the outlet one way.  3-conductor wire has “inner” wires with different color insulation, normally green for ground, white for common, and black for the power side.  Again, using the same color connections for the replacement wires will result in a properly performing and safe appliance.

 

I hope all your projects go well.  Thanks for reading, and happy restoring!

 

Ed

 

If you’d like to download a PDF of this “Ideas” column, click here:


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