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I have a 3 prong plug for my dryer. When I take a voltage reading between X and Y I am getting 320VAC. Between X and W or between y and W I am getting 160VAC, and my dryer has quit running. Can you give me an Idea what would cause the odd voltage?

  • What reading do you get at a standard outlet? – isherwood Oct 15 at 2:41
  • Hello, and welcome to Home Improvement. We'll need some more info before we can help you. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Oct 15 at 4:08
  • What readings do you get at a regular outlet, and what are you testing this with? Also, is this in a single-family house or an apartment of some sort? – ThreePhaseEel Oct 15 at 4:14
  • Where in the world are you (country) ? If outside the US do you know if you have 3 phase power. – Ed Beal Oct 15 at 13:36
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The readings you are getting are entirely correct. The problem is that you are misinterpreting the results. When we speak of AC voltages there are several types of measurements that may be taken. Specifically of interest here are:

1) Peak voltage 2) RMS voltage

If you want to dig into the theory of this please see:

RMS Calculations

But the bottom line is that the relationship for a SINE WAVE is:

Vrms = Vpeak * 0.707

In your case you measured a PEAK value of 320V/160V. If we convert to RMS we get:

320 * 0.707 = 226V
160 * 0.707 = 113V

These values are slightly low but well within the "normal" range of AC mains voltages. The specification at the point of usage is 105%-90% of the 240/120 nominal which means that the H-H line should be above 216V and the H-N lines should be above 108V.

More on that here:

Voltage Range

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