Voltage Runs up to 137 when Dishwasher Starts

[kosullivan]

I was called to a house where the owners UPS (APC 750 KVA) was shutting down because of overvoltage when the dishwasher or washing machine was turned on. I put two digital voltment meters on the PC circuit and the starting voltage is 122 to 124 with no appliances on and when the dishwasher or washing machne is turned on the voltage RISES to 135-137 volts on the DVMs.

I've never seen this situation before and am used to voltage drop as loads are added. When we put the heat pump on the voltge dropped from 124 to 122. The "A" and "B" legs at the panel are balanced and have the same high voltage. House is aerial fed from a pole about 150 feet from the house. Several incadescent blubs have blown when the appliances are turned on.

Any comments and ideas would be apprecited. I've never seen this before.:-

 

[iwire]

There is a bad connection or completely open neutral somewhere between the service panel and the utility transformer.

 

[LarryFine]

The "A" and "B" legs at the panel are balanced and have the same high voltage.

Not at the same time.

 

[brian john]

I assumed you measured this voltage at the service panel?

If so as noted above look for the neutral connection issue all the way to the utility transformer.

 

[ptonsparky]

Is the PC circuit part of a MWBC that includes the dishwasher/wash machine? Again, loose neutral somewhere.

 

[danickstr]

I was wondering about MWBC too, but since Bob and Brian did not mention it, there must be a telltale sign that it is not the issue of which I am not aware.

 

[iwire]

I was wondering about MWBC too, but since Bob and Brian did not mention it, there must be a telltale sign that it is not the issue of which I am not aware.

I think Tom's suggestion is right on, I did not mention it because I did not think of it. It never struck me that the DW and PC would be sharing a MWBC.

That would also explain the voltage at the panel remaining steady.

 

[LarryFine]

It never struck me that the DW and PC would be sharing a MWBC.

"Excuse me, sir. Seeing as how the V.P. is such a V.I.P., shouldn't we keep the P.C. on the Q.T.? 'Cause if it leaks to the V.C. he could end up M.I.A., and then we'd all be put out in K.P." ~ Robin Williams as Adrian Cronauer in Good Morning Vietnam

 

[jerm]

If it's a SmartUPS 750 (as opposed to the not-as-intelligent BackUPS 750) then you can adjust the sensitivity quite a bit and just have it deal with the voltage problems. Then it can just kick over to battery when the voltage spikes, but it won't beep at them anymore. You'll need a serial cable.

Just in case you never find that loose neutral.

Good luck to you.

 

[brian john]

I am with Bob on this...Quick snap answer without all the options. Just how my brain works, my apologies.

 

[kosullivan]

Thank you for your replies

Thank you for your replies

Thank you for your replies. I appreciate ALL the suggestions and will post what I find.

Thank you again.

Kevin O'Sullivan P.E.
Master Electrician

 

[kosullivan]

Results of Utility Company Visit to Site

Results of Utility Company Visit to Site

Thank you all for answers to my question. Here is the outcome.

The Power Company came out on Friday and confirmed the high voltage situation. When they went up in the bucket truck to look at the transformer connections they found that the squirrels had eaten through a part of the carrier wire / neutral that feeds the house in the overhead service. They cut out the bad section and spliced in a new section of wire but the overvoltge just dropped a few volts ... but still remained over 130 volts when the washer and dishwasher were turned on.

They said that this happens occasionally and that the squirrels eat through the wire as they sharpen their teeth. It is a long run to the house that is set back on the property and they will be back on Monday to string a new service drop. They didn't have a long enough piece of cable on the truck.

Kevin O'Sullivan, PE