Confessions of an Electrophobe (Part 2)

By , April 15, 2013

In my last post, I cracked my facade of cool, logical, competent home electrician, calmly installing a set of 12 volt outlets in our cabin. The confession continues . . . .

Belatedly remembering how one is supposed to connect a fuse did not solve the white stripe wire problem. I set up the outlets “correctly,” according to my understanding of what the white stripe represents, and plugged a charger into it. Nothing happened, so I pulled it out and tested one of the outlets with my voltmeter. It gave me a negative value, indicating that I had crossed negative to positive.

I puzzled overly long on how the power could be switched when I’d wired it “correctly.” Careful observation of my components only confounded the situation.

I examined the plug that I’d cut off. Most of these “cigarette” plugs house a tube fuse in the cylinder, behind the positive contact button. This plug has a 15 amp bayonet-style fuse pressed into the side of the cylinder. The fuse is located on the same side of the cylinder as the black wire leading into it. From all appearance, the black wire contains the fuse. Therefore, the black wire should be positive, and the white stripe wire has to be negative.

If the fuse (blue bar in top of plug) joins positive to positive, then by looking at it, one would assume the black wire is positive. Right? Wrong, apparently (Photo: Mark Zeiger).

If the fuse (blue bar in top of plug) joins positive to positive, then by looking at it, one would assume the black wire is positive. Right? Wrong, apparently (Photo: Mark Zeiger).

I couldn’t open the cylinder to confirm this, but common sense indicated that I shouldn’t need to. If the white stripe wire were positive, then the wires would probably need to be twisted inside the cylinder housing in order to connect with the fuse on the other side of the unit. Either that, or the contact wires from the fuse lay across the negative wire to reach the positive side.

Eventually, I had to bow to the evidence of my voltmeter, ignore what appeareed to be the truth, and switch the wires. I also had to go back to the old outlets, and recognize the mistake I’d made concerning the bar, as I explained in the previous post.

After I gave in to the inevitable, the outlets worked as intended. Unfortunately, we lost the charger I’d initially plugged in; it is not fused, so the reversed wires fried it. It’s not a unit that can be opened up and repaired. Thankfully, it was our cheapest and most disposable charger. In hindsight, though, I should have used one of the higer end, fused plugs. The fuse would have blown, I could replace it in 5 seconds, and the unit would become operational again.

Once we reconnected our system, I went on line to research wire markings. I found that the white stripe is “always” negative if you’re wiring floor lamps. If you’re wiring vehicles, the white stripe is “always” positive, except when it’s not. The less dogmatic Web sites admitted these standards are often ignored, and that the only safe way to proceed is to test each appliance that contains a white stripe wire!

Because the outlets I installed in the cabin were designed for use in a car, I should have assumed that the vehicular “convention” applied. However, since I don’t work on our car frequently, I am unfamiliar with the convention. Nor have I found any reference book in our home that explains this.

Throughout the installation, at every moment of decision, doubt, or hesitancy, I reached for a reference book. Our main 12 volt resource is Charlie Wing’s Boatowner’s Illustrated Electrical Handbook (check your local, independent bookstore). It helped somewhat. For instance, it confirmed my mistake about the placement of the fuse. However, it didn’t offer any clues as to what a white stripe indicates. Wouldn’t you think this might be considered fairly basic DC wiring information?

Each time I stopped my work to search for an answer, Michelle and I discussed our frustration. Why couldn’t we flip to a page of basic yet vital information that would remind us how to do the right thing, without the sparking, yelping and leaping back?

No book we own seems to include this helpful feature. This led me to take steps that will improve our electrical work in the future. I’ll elaborate on that in the next post.

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