Calculating Power

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I have an electric massage machine that has this nameplate information: INPUT: 120V,60Hz,0.3A. I would like to use it abroad with 220V. Can you tell me how big of a converter I need? I don't know how many watts this uses.

A little background might be in order to answer this question, but don’t worry – the math is pretty simple!

Power is measured in Watts when using a DC (or direct current) circuit. This is the type of power supplied by a battery. When looking at AC (alternating current) circuits – the power that you find at your wall outlet – power is measured in Volt-Amps or (VA). When looking at the nameplate of an electric device, you will most likely see power listed as VA, although sometimes it will be shown in Watts. For our purposes, it’s OK to consider these values one in the same.

The formula to find power is:  P= V x I, where P is power (VA or W), V is voltage, and I is current (usually shown in amps or A).
So, looking at the example above, this machine uses (120volts x 0.3amps) 36VA (or 36 watts if you prefer).
The original question was how much power is used at 220 volts. The thing with power is that it doesn’t change – it is the fixed demand of the appliance. But, something has to change. Using simple algebra, we find that our current draw is approximately half of what it would be at 120 volts (I= P / V) – roughly 0.16 amps.

While it’s interesting to note how current draw changes inversely proportional with voltage, the important thing to remember is that this machine will use 36 VA (watts) whether here or overseas.

Now for the final curve ball! AC voltage is delivered in frequency cycles, called Hertz or Hz. In the United States, our standard is 60 Hz. Many other countries also follow this standard, but some do not. You may find that a country you’re visiting uses AC voltage at 50 Hz instead. If this is the case, you will not be able to use your 60Hz electric equipment – even with a voltage converter. If it’s something you absolutely need, you’ll have to purchase a 50 Hz equivalent where you’ll be visiting.

I have two electric dryers, both have 3 wire hook up. One dryer has wires colored black/neutral green/red. The other dryer that I want to use instead has yellow/neutral green/red. Can I use the black wire in place of the yellow wire?

Your description of the wire doesn't make sense to me. Usually ungrounded (hot) conductors are any color other than white, gray, or green. Neutral (grounded) conductors should be white or gray. Grounding wires are green, or sometimes green with a yellow tracer.

Wurtsboro Electric Service, Inc.

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