AC voltage testing


Old 07-21-08, 08:22 AM
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AC voltage testing

I just tested a few random receptacles and discovered that the multimeter ac voltage readings are consistently 138-144. These are generally on 20 AMP receptacles on 12 gauge wire, from what I can tell so far.

Im not an electrician but I think of voltage as the "pressure" on a system. 20amp/125 V receptacles seem to be the norm in this house but Im still concerned that the "pressure" is way too high.

Should I think of lowering the AMPs on the circuit panel down to 15. I haven't tested any 15amp circuits yet but I will today.

This is all on a 200amp circuit panel (why so high? Im not sure but it was done within last few years, I'm the lucky new owner).

Please tell me my family and I can sleep soundly tonight.
Any response is greatly appreciated.
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Old 07-21-08, 08:35 AM
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Get the diffrent voltmeter to make sure the reading is the same as the first voltmeter is sometime some digtail voltmeter may not read correct voltage espcally when the battery in the digtal meter is not strong { near dead batteries } will give a funny reading there.

Myself I always carry two diffrent voltmeter to verify it in case one not reading correct.

If you can ask one of your neghbor to borrow their voltmeter that will be fine and compare the reading or go to the big box and get new voltmeter.

Now 138~144 volts that is way too much do you have any 240 volts device running now ? if not turn all the 240 volts devices off and read the voltage again if still high call the POCO NOW don't wait too long sound like you have either too high a voltage or semiopen netual which both are very dangerous and that need to be taken care now.

The POCO useally don't charge anything comming out to take care their end and they will let you know what the situation.


POCO = Power Company
Old 07-21-08, 08:48 AM
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If you can't borrow another meter go to the house of a friend who lives several miles away and try it there. A neighbors house won't work for this test because there is a slight possibility of a neighborhood-wide POCO problem.
Old 07-21-08, 09:36 AM
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I just put in a new battery and I get normal readings. The law of Parsimony I believe is the simplest answer is usually true. And here I was worrying about Ohms law.

Wow...I feel like I over thought this one and spent way too much time on it. But I feel way better. Thanks.
Old 07-21-08, 07:19 PM
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You would not have been able to change the voltage even if it was high.
This would be an issue for POCO and their transformer.
Changing a breaker only changes the amount of current that can flow over a given time period, not the "pressure".
Old 07-21-08, 07:43 PM
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The voltages you mentioned 140 vac and higher can be dangerous and cause a possible fire or equipment failure over time. You should contact your utility company ASAP! You can also see if your neighbors have elevated line voltage.

Most people would have no knowledge of this unless they measure the line. The only indication most would have is brighter bulbs and bulbs that burn out much faster.

I had a similar situation several years ago and I had at least one wall transformer (the little black ones that power and charge devices) burn out as a result. It turned out it was a tap on a transformer at a substation a mile away! In that case about 1000 residential customers had the problem. I was the only one to report it but later others also found they had equipment failures. Having a higher voltage like this for a brief period is not a problem, it is when it exists for a longer time.

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