The Amp, the Watt, and the Volt: The Three Musketeers


Electricity Simplified

This article refers to the amp (short for ampere), the watt, and the volt as the Three Musketeers because both groups are, as it were, inseparable. Like the song lyric from Love and Marriage states, You can’t have one…without the other.

How so?

Let’s take the example of household wiring, the standard voltage rating being 110 volts (although it can run as high as 120 volts) or, for appliances such as electric dryers that need a lot of power, 220 volts (which can run as high as 240 volts). For the sake of simplicity, we’ll “assume” that all wiring being discussed as the 110 volt version…and yes, I do know what about the definition of the word assume.

But it gets too confusing otherwise. Using a single voltage for our illustrations will make it easier to comprehend the relationship between amps, volts, and watts…and once those are understood, you can play around with any voltage number you like.

Oh, you want to know what all these words mean? Okay, okay. Hm. The scientific explanation is ridiculous unless you’re a scientist…the water analogy is often used and yes, it’s a little easier to understand, but…okay. How about a boxing analogy?

Suppose you have a really good fighter in the ring and he throws a real zinger of a punch that connects perfectly and knocks his opponent clear out of the ring. The punch was magic. It was fast, it packed…well, punch…and it even wore out the boxer who threw it, because he put all he had into it. Got it? Then think of electricity this way:

    The speed of the punch is the amperage (Amps!)

    The power with which the victim was smacked is the voltage. (Volts!)

    The drain felt by the boxer who threw the punch is the wattage. (Watts!)

    Our old friend Reddy Kilowatt might have a better explanation, but we don’t see him around much any more.

Our old friend Reddy Kilowatt....

Our old friend Reddy Kilowatt….

The Three Formulas

Remember I said the Three Musketeers were inseparable…and so were the watt, the volt, and the amp? The reason (on the electrical side, anyway) lies in the three formulas. These can be found in a gazillion places on the Internet and in every basic wiring book out there, but here they are–just so you don’t have to hunt them down:

    Watts = amps multiplied by volts

    Amps = watts divided by volts

    Volts = watts divided by amps

Hang in there. We’re actually getting to the part that might actually be useful. At any rate, I know that the place I use these formulas again and again and again is when I’m trying to figure out one of three things:

1. Is it safe to fire that back massager up using our smaller generator, or must I start the big gasoline hog to give my wife’s knotted muscles a bit of relief? (At the present, portable generators serve as our only sources of AC electricity for the household.)

2. How big a junction box must I install for the house we’ll be building next year?

3. Will I need heavier than usual circuit wiring for the electrical supply to the heater in the storage shed during the winter?

Things like that. Here’s a closer look:

1. The massager. We know it runs on 110 volt current. The label states its power usage as 1.2 amps. Uh-oh, no wattage? Oh, no big. 1.2 (amps) times 110 (volts) comes out to 132 watts. Hey, that’s cool! We try not to run more than about 300 watts at a time to save wear and tear on that little Yamaha generator, but if we shut off the TV, we’ll be well under that figure. It’s all good!

2. The size of the junction box. Forty years ago, you seldom saw residential junction boxes that were set up to handle more than 100 amps. With only a few lights and an electric radio and possibly a TV set, that was plenty. Now a 200 amp installation is fairly common–unless you’re Michael Jackson, and I’ve no idea how much electricity that man poured through Neverland in its heyday. I’ll probably go with a box that can handle 200, though we’re pretty conservative in our power usage these days and may never again need that much. It just pays to have capacity in reserve. I could add up all the likely appliances and crunch the numbers, but there’s no real need. The same is likely true for you…unless you’re building a humongous music studio into your home or some such.

3. The storage shed. We need to keep that toasty warm through the winter because of the cat that lives there. She’s a cool kitty, but she doesn’t play well without our other two in-house cool kitties. A 1500 watt heater from Wal-Mart will do the trick. So here’s the math: 1500 watts for the heater…100 watts for an incandescent light bulb (I detest flourescent)…and another 35 watts in case I want to play a radio when I’m hanging out with Green Eyes. (Well, that’s our shed kitty’s name.) Total wattage: 1635.

Okay, then, 1635 watts divided by 110 volts comes out to a hair under 15 amps. All righty. It’s best to have something left over for a margin of safety when playing with electricity, so a 15 amp circuit would be too light…but I was figuring on a 20 amp circuit for that piece of wiring, anyway, and 20 should be enough.

How about that. Now we’ve gained some practical advantage from knowing the relationship between the volt, the amp, and the watt (not to mention the Three Musketeers), and it didn’t even hurt.

Not very much, anyway.