outlet voltage drop

I have a toaster oven and a microwave in the same outlet. A couple of window fans are running on the same breaker.

If the toaster oven is on, the voltage at the outlet drops about 4 volts.

If the microwave is at half power (it's a 1300W unit) the drop is about the same.

Is this typical, or is it a sign of too much resistance somewhere, which would be getting hot?

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Reply to
Tom Del Rosso
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Not enough information. How long is the wire to the breaker, and what gauge? If the line is at 130 volts, that is a 10 A load. A 4 volt drop would dissipate 40 Watts. This would indicate .4 ohms in the wiring. If it was all in one spot, it would be a problem. In a kitchen that should be a 20A circuit, with 12 AWG wire. That has 1.588 ohms per

1000 feet. Double that for the two wires, for 3.176 ohms per 1000 feet, or about 125 feet of wire from the breaker box to the outlet. If the outlet is old or damaged, have someone who knows what they are doing replace it. There is also some drop in the wiring from the power transformer, and some sag in the windings.

What is the voltage between the neutral & the ground pins, under load? If it is half the drop for the load, it should be OK. The ground doesn't carry any current, and doesn't have a voltage drop. If there is much variation, check for a loose or open neutral. Overall, that doesn't sound too bad.

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Reply to
Michael A. Terrell

Michael T. has all the right questions. I'll add a bit more by asking where are you measuring the voltage? Inside the microwave oven, at the wall outlet, or at the breaker box? Assuming you're in the US, 4v out of 120v (instead of 240v) is 3.3% which is fairly small.

So, let's do the math. I'll guess you're measuring at the wall outlet because it's the most convenient. I'll also guess that you have about

50ft of #12 AWG solid wire in the wall to the breaker box. At 0.00187 ohms per ft, that's 0.187 ohms resistance. There's also some resistance between the breaker box and the transformer on the pole, but that's much heavier guage wire, so I'll ignore that. However, I'll round the resistance up to 0.2 ohms so I don't have to find my calculator.

At 1300 watts and 120v, your microwave oven draws 10.8A. The voltage drop in the wiring is: 10.8A * 0.2 ohms = 2.2volt Ok, so it's not 4v, but it's close enough since I ignored outlet contact resistance, screw terminal resistance, drop across the breaker, temperature, and made assumptions on the house wiring gauge and length. Change the numbers to fit your situation and see if it comes closer to your 4v measurement.

The typical toaster oven burns about 1400 watts, so it's comparable to the 1300w microwave oven in power line drop.

The window fan will have an effect on the line drop, but since you didn't specify whether it was running during your measurement, I can't guess what the effect might be.

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Reply to
Jeff Liebermann

In addition to what Michael and Jeff said, I suggest inspecting the outlet and every outlet on that circuit from the breaker onward.

Please replace any outlet that is installed using the 'backstab' method:

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At the very least, remove the stabbed wires, clean them and then use the screw terminals instead.

--Winston

Reply to
Winston

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