Sunday, February 3, 2008

Wattage Around the House

How do watts figure into your electrical calculations? It’s simple: They tell you how much stuff you can pile onto one circuit without overloading it. You don’t want to put too much demand on a circuit with too many watt-hungry loads. Some simple math will keep you on the right track.
Watts equal voltage times amps. Let’s say you want to install a new 15-amp circuit so you can add some outlets or lights to your living room and dining room. Because you won’t be running any major appliances (assuming you don’t do your laundry in the living room), this circuit will be running on 120 volts rather than 240. Therefore … 120V X 15A = 1,800 watts

Terrific, you say. I can put in 18 100-watt lights. Actually, you can’t, because you generally figure on running only 80 percent of the maximum load —1,440 watts in this case—but that’s still 14 lights with watts to spare. What if you want to plug in your new window-shattering, guaranteed-to-have-theneighbors-call-the-police music system that needs 1,900 watts all by itself? Time to recalculate. It’s going to need its own private 20-amp circuit before you can crank up Eric Clapton’s original version of “Layla.” By calculating your electrical needs first, you can accurately wire your house once without needing to make adjustments later.

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