DC Cheat Sheet

By , April 17, 2013

In the last post I complained about searching for basic electrical information, such as wire color coding, in the middle of an electrical project.

This happens all the time. As the years and projects pass, I retain more and more electrical information from one task to the next. But, as I face each new job, my stress level increases to the point that I’m more likely to forget what little I do know, and less likely to reason out what I don’t. In the heat of battle, as it were, I often can’t keep enough composure to remember the simplest things.

A classic example: my voltmeter is set up to measure AC and DC loads. I turn a dial to the type of current I need to measure. But, they’re not marked “AC” and “DC,” they’re marked “V” for volts, then a symbol— “~” (tilde) for AC, and a solid line with a dashed line underneath it for DC.

In calmer moments, I can tell you that the ~ stands for AC. Alternating current oscillates, making a sine wave, which the tilde represents graphically.

More critically, which wire do you disconnect from the battery first, negative or positive?

Each adjustment to our electrical system is filled with such moments. Even so, none of my reference books, even the most insultingly simple ones, seem to contain this information. It’s almost as if the authors assume that the basics of electrical systems and machinery are so self evident, they need not be explained. The overwhelming message seems to be “Everybody knows that!

Well, forgive me, but I don’t innately know these things. Nor, when the hot wires are exposed, do I seem to be able to remember with certainty the information I’ve had to look up in the past. All those vital little tidbits of knowledge fly right out of my fevered, electricity-fearing brain right when I need them most. I may have a good idea of what I’m supposed to do, but I’m not willing to gamble my skin on it.

After my most recent electrical work, I decided that if I want this elusive reference sheet, a DC Cheat Sheet if you will, I have to create it. As soon as I’d finished installing the 12 volt outlets, and had researched what that damned white stripe wire might or might not mean, I set to work.

My first, most obvious step, was to create a heading on the document: the words, “DON’T PANIC” in large, friendly letters, to tip my electrician’s cap to Douglas Adams.

Next, I listed basic truths of electricity that I need to know when the wires are live, and death or severe burns threaten. Many of these are judgement calls, so one of the many benefits of this list is that it codifies the “house rules” of electricity.

For instance, after listing the “standards” for white stripe wires, I specified that in this household, the white stripe always denotes positive. That will be our standard, and it will not vary.

I also codified disconnecting negative first. This is the automotive rule, because the negative wire grounds out on the vehicle frame. Separating that connection makes working with the battery safer. I have not found a reason to do the same in our home system, except that if I get used to doing it that way at home, I’m less likely to forget and make a mistake on a vehicle, when it definitely could cause problems.

The DC Cheat Sheet is a work in progress at the moment, but before long I’ll start printing copies of it to slip into the front cover of all my reference books that deal with electricity. If it doesn’t solve my problems, it’s at least a good start. And who knows? It might just save my life.

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