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Old 08-02-2013, 07:51 PM   #1
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Excessive Voltage


Digital voltmeter reads 180v, and then drops to 0 on a mwbc, receptacle.

The current setup is 2 SP 15 amp breakers (no handle-tie) used for the branch circuits.

Turning off one of the two breakers causes the voltage to read normal. This breaker is feeding the refrigerator, and a range hood; possibly kitchen lights as well, I don't recall.

If both breakers are on, everything works for about 15 minutes, then the bedroom and bath lights, receptacles go out, without tripping the breaker.

I know this needs to be on a DP breaker, in order to shut of both phases at the same time, but 2 SPs wouldn't cause this problem would it?

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Old 08-02-2013, 08:51 PM   #2
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Excessive Voltage


I caught hell for my 'test' suggestion...but it looks like this is a good way to find out the problem.

Turn off one breaker. Using an iron...plug it into an outlet that is on the ckt that is still live. Measure the voltage before you turn on the iron...then turn on the iron. Assuming a typical 1200w iron....you should only see 2-4 Vac drop.

Turn off that breaker and turn on the other.

Repeat above test on the other section.

If you have a loose neutral or bad breaker.....this should help you figure it out.

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Old 08-02-2013, 09:27 PM   #3
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Excessive Voltage


Are we assuming a bad breaker, in addition to a loose neutral?

I've looked at tall the devices, lighting fixtures, and panel, with no loose neutrals noted.
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Old 08-02-2013, 09:29 PM   #4
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Excessive Voltage


More than likely a loose neutral. I had the same problem and was a loose neutral at the juction
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Old 08-02-2013, 09:43 PM   #5
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Excessive Voltage


bad neutral connection.... re check all the splices in that circuit. A bad circuit breaker would not create a high voltage issue, just so you are clear on this.
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Old 08-02-2013, 10:15 PM   #6
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bad neutral connection.... re check all the splices in that circuit. A bad circuit breaker would not create a high voltage issue, just so you are clear on this.
OK, well I'll go back tomorrow and look at the recep behind the refrig, which one-half of the mwbc feeds, I didn't get a chance to look at that tonight, so the loose neutral could be there.

This is crazy tho because as I was testing the bedrm recep (showing 180v then down to 0), I had my buddy turn off the two breakers one at a time, and once the refrigerator brkrs was off, the reading was normal. THEN, I ended up reconnecting the brkr as it fed the refrig, and everything worked for about 15 min. NOW, we're back to lights out.
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Old 08-02-2013, 10:32 PM   #7
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Excessive Voltage


The ONLY way a voltage can high on a MWBC is a loose neutral. Check all your neutral connections.
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Old 08-02-2013, 10:42 PM   #8
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Excessive Voltage


Thanks Joe, will do.
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Old 08-02-2013, 10:44 PM   #9
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Hey, in addition to this, during voltage checks, I found 135v between neutral and phase at the Main Breaker. Any concern on this?
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Old 08-02-2013, 10:56 PM   #10
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Excessive Voltage


Quote:
Originally Posted by sirsparksalot View Post
Hey, in addition to this, during voltage checks, I found 135v between neutral and phase at the Main Breaker. Any concern on this?
135 volts?? did you use one or two differnt voltmeter to make sure?

If one read 135 volts the other side of line et netural will read lower but add two together it will always the same ( line to line )

I will grab a second testmeter to verify it and if still verifed with that high a voltage then call the POCO asap and just say " bad netural connection " that all nothing more they will come out pretty fast with it.


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Old 08-02-2013, 10:58 PM   #11
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Excessive Voltage


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135 volts?? did you use one or two differnt voltmeter to make sure?

If one read 135 volts the other side of line et netural will read lower but add two together it will always the same ( line to line )

I will grab a second testmeter to verify it and if still verifed with that high a voltage then call the POCO asap and just say " bad netural connection " that all nothing more they will come out pretty fast with it.


Merci,
Marc
Thanks Marc, it's the only tester I have right now, maybe I can get a different one tomorrow.

There's also in excess of 240 L-L.
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Old 08-02-2013, 11:02 PM   #12
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Excessive Voltage


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Thanks Marc, it's the only tester I have right now, maybe I can get a different one tomorrow.

There's also in excess of 240 L-L.
I will suggest just go ahead and call the POCO and let them deal with oddball voltage so they can check their side to rule it out before anything else do get damaged with high voltage level.

Once the POCO verifed on their side we can go from there.

Merci,
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Old 08-02-2013, 11:02 PM   #13
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Excessive Voltage


Quote:
Originally Posted by sirsparksalot View Post
Hey, in addition to this, during voltage checks, I found 135v between neutral and phase at the Main Breaker. Any concern on this?
Yes.... Makes you think of a bad service neutral...... but I do not understand the lights/receptical going out....??????

The varience in voltages (due to a bad neutral) can be explained by varying loads (maybe you turned things on or off or refer went on or off) but I don't understand the lights going off (perhaps blowing out) but not turning off.
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Old 08-02-2013, 11:12 PM   #14
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Excessive Voltage


A true MWBC will use red et black line conductors so to verify that you will have to take the breaker cover off and see what colour conductor itself is.

And take a quick look at netural bussbar ( do not touch anything at the moment ) but just look at it and see if you did see any burnt mark on them if so then it will tell you that you have loose connection on the netural bussbar if none.,

Then possiblity that one of the junciton box may have bad splice on them so you will have to find each one as you work it way down.

What year this home was builted and was rewired sometime back or just oringail wiring in there?

Merci,
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Old 08-02-2013, 11:15 PM   #15
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Excessive Voltage


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Originally Posted by MTN REMODEL LLC View Post
Yes.... Makes you think of a bad service neutral...... but I do not understand the lights/receptical going out....??????

The varience in voltages (due to a bad neutral) can be explained by varying loads (maybe you turned things on or off or refer went on or off) but I don't understand the lights going off (perhaps blowing out) but not turning off.
Beats the hell out of me too. I guess a breaker should trip w/ excessive current if the voltage increased, given the same load resistance??

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