AC Problem

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Old 07-05-18, 09:37 AM
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AC Problem

Need help figuring out problem. Main feed on sub panel has low voltage on 45volts on one leg coming in. Went to main panel and the feed breaker shows 120v on both outputs of the breaker. I measured neutral to main feed to output of the 200 amp breaker. I removed the low voltage feed wire at the sub panel and still read the low voltage. Could the Main 200 amp breaker be defective. I tried measuring a voltage drop across the the Main breaker and it read 0.0 Volts.
 
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Old 07-05-18, 02:14 PM
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Welcome to the forums.

Be very careful using your meter in the ohms setting when something is powered.
You should be measuring 240vac across the main breaker.
 
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Old 07-05-18, 03:20 PM
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When hot to neutral on one leg was 45 volts, what was hot to neutral voltage on the other leg at the same time?

You could have a bad neutral to that subpanel.

Do not touch meter leads to powered circuits when testing ohms or resistance or continuity.
 
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Old 07-05-18, 06:11 PM
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Yes one leg hot to neutral was 45 volts the other was 120 volts.
 
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Old 07-06-18, 08:28 AM
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This is probably a bad feeder breaker or cable. Were the measurements taken with electrical load on the service? I'm also not clear on exactly what is the main and sub on your descriptions.

Generally you would have a feeder from the power company, through the meter, then into a main breaker in the main panel. A feeder breaker in the main panel would energize a feeder cable to a subpanel which may or may not have a main breaker in it. Does the subpanel feeder cable run underground?

Exactly where are the measurements taken and which devices are/are not working?
 
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Old 07-07-18, 07:49 AM
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The wiring is exactly as you've described. The meter readings were taken at the sub panel. The sub panel does have a main breaker So I took off the wires at the main breaker in the sub panel off and was reading 120v on one leg and 45v on the other. I went back to the main panel and read the power at the main breaker that feeds the sup panel and both legs read 120v under no load. The wire is 4 strands of 2AWG running underground that was just installed two months ago with no connections in between the main breaker and the sub panel main breaker. This has been working fine for the past two months. I went ahead and replaced the Feeder breaker in the main panel and the problem has gotten worse. Now Im reading at the sub panel 120v on one leg and 7v on the one that was reading 45v before. This is really baffling could it be a defective meter on the power pole?
 
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Old 07-07-18, 01:18 PM
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In your main panel, check voltage across the incoming feeders from the meter. Check ahead of the first main breaker. Check hot leg to hot leg, should read around 240 volts. Now, check each hot leg to neutral, each should read around 120 volts.

You asked:


This is really baffling could it be a defective meter on the power pole?

Is there a disconnect at the meter on the power pole? If so, check voltages at that breaker disconnect too, both before and after this disconnect breaker.
 
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Old 07-07-18, 01:47 PM
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It sounds awfully quick, but it sounds like one leg has gone bad underground .
 
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Old 07-07-18, 01:58 PM
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It sounds awfully quick, but it sounds like one leg has gone bad underground .

My first thought as well, but we know nothing about the type of wire or installation method that was used. I have even seen direct buried NM cable last 5 or 6 years without going bad. The same with NM cable strung through the trees, I was amazed. My father-in-law was unbelievably cheap.
 
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Old 07-07-18, 05:00 PM
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Ok read 240V across the two hot legs coming from the meter to the Main breaker, measured 120V on each leg to neutral on the breaker. the really weird thing is that I read 7V this morning at the sub panels main breaker one leg and this evening it was reading 97v until I applied a load and the it went to 5V.

The wire is four strands of aluminim 2AWG 150ft from the main panel to the sub panel buried 3ft underground in sand.
 
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