Build your own RV extension cord?

We've all had the experience: We have the rig settled at a friend's house, not really set up for an RV. Then we find we're just a wee-bit short when trying to plug your RV shore power cord into the outlet. It's a frustrating experience, and there's always the temptation to use an adapter and a light duty extension cord to make up the difference. Please don't. Electricity is a funny thing--when too "light" a wiring is used, not only do you endanger yourself with fire, you also run a good risk of damaging expensive RV equipment.

Here's the deal: Electrical wiring actually does have a certain amount of resistance to the flow of electrical current. The longer the wire run, the greater the amount of resistance. As the electrical current struggles against this resistance, it produces heat energy—hence electrical cables can actually get hot--sometimes hot enough to create that hideous problem known as fire. What usually "goes first," however is the under-rated fittings on the end of the cables. These can overheat and burn up, or on the way to that create even greater resistance to electrical flow. But even if that doesn't occur, the resistance of the wiring actually reduces the amount of voltage that can reach your RV.

photo: .ci.wausau.wi.us

So if you have too small an extension cord out to the RV, and then fire up a big power consumer—in the summer think air conditioning—and not enough voltage is present, then physical damage can happen to devices that need that power. So how do you work with this problem? Well, you could purchase a ready-made RV extension cord. For the 30 amp RV crowd, a 25 foot cord will probably set you back fifty to sixty dollars. For the 50-amp users, that same length could run you over three times that price.

Tempted to "do it yourself," and build an extension cord? It's do-able. But you need good working data on what size conductors to use in your cord. With the advent of the Internet, there are all sorts of sites that can help you figure out what your wire requirements are. Check out the sidebar for this story. But as you run your calculations, be sure to take into account the length of your existing RV shore power cord. One of our rigs has a 25' shore power cord, so building an additional 25' of extension cord would require figuring a full 50' run. Whatever you do, don't skimp on the wire gauge or the fittings.

If you decide to build your own, always double check your connections before putting your cord into service. We use the ohm meter portion of a digital multimeter to verify that everything it where it should be. Imagine our surprise when we completed a cable and we found two of the conductors reversed. How'd that happen? Squinting through bifocals at the included wiring diagram for one of the fittings, a slight misinterpretation of what the fine print and finer arrow we're pointing to led to what could have been a real problem.

If you're the least bit squeamish about your ability, drop the bucks on a commercially built unit.

And one more thing, when you use any shore power cord, it's never a bad idea to pull all the shore power cable out of the compartment before hooking up and using the shore power. Why? Well, since cable does have resistance, if you put enough load on your shore power cord, you could actually have the equivalent of a "heating cable" in your cabinet--like those things those poor folks in the north use to keep their pipes from freezing in winter.

Here's a resource for the do-it-yourselfer. This link will take you to a great calculator for figuring wire size needed.