262v on 120/240 single phase resid service

[FREEBALL]

I did a job today where I had to make the receptacles hot all the time, the switches were switching half of receptacles originally. I was installing ceiling boxes for lights/fans. Anyway I simply tied the switch legs together at switch however when doing so I checked voltage and found 138v. So now Im thinking there must be a 3 wire feeding the circuit and we lost a neutral, went to panel, and there are no 3 wire circuits, I turned off everything and checked main voltage in it was 262, by the time I turned all on again I rechecked and it was at 241. Anybody see this before the service is fed underground from a padmount poco transformer that feeds 2 other homes. I continued to recheck but voltage stayed the same from there. I told the customer he needs to call poco. Side note I found a single 6/3 seu cable being fed from 2 sp qo20 breakers and asked what this was and the cust. said he thinks the stove. I said really, its electric range. I checked and sure enough it was he stated that they bought 2 stoves in the past years because the breakers kept tripping so Im going back to fix that tomorrow, he said the appliance company installed them. Unreal. I did install an AFCI on the circuit for the lights and the customer was appreciative of this, and after explaining to him what protection this gave him, there was no mention of the price difference between a standard breaker which he got in a previous quote. Anyway just wanted to throw out the incoming voltage issue for ideas

thanx

 

[PetrosA]

If the home was in an area that got hit hard by the storm, it could have been fluctuations while crews worked on primaries.

 

[Smart $]

Another possibility is the POCO is using an undersized transformer and they know the voltage will sag under heavy load, so they used the next lower voltage tap on the primary. When you checked the voltage and got a high reading, the transformer was lightly loaded (in part by you turning everything off). When you turned everything back on, the transformer was more heavily loaded, especially if an AC load kicked on. The voltage also depends on the load of the other 2 homes at the time you are measuring.

FWIW, 262V is still under 240V +10% (264V). I think POCO's typically try to stay within +5%, but going to +10% is not unheard of if they know the transformer is undersized for stiff voltage supply.

 

[meternerd]

Just some info....POCO normal voltage control limits are usually 120V +/- 5%..that means voltages are allowed from 114 to 126V. Outside that range will usually mean a regulator of some sort. Most distribution substations I'm familiar with have voltage regulators or load tap changers (LTC) that control line voltage. Taps are 16 raise and 16 lower with 5/8% per tap. That means that if neutral (no correction) voltage is 120V (measured at the low voltage control transformer secondary) the regulator can control +/- 10%. Most are set at 124 +/- 2 Volts. During distribution system switching, voltages may be higher or lower. But...there is a time delay (usually 30 sec) before the regulator corrects over or under voltage. That reduces tap changing during momentary sags or surges. You may have seen a surge before the regulator operated. If you are downstream of a line voltage regulator, rather than a substation regulator, the times are longer, usually 15 seconds longer than the regulator upstream. Switched capacitor banks can also affect voltage. Voltages near a substation or regulator will be higher due to voltage drop on the distribution lines. I know....way too much information, but I thought some folks might be interested.:happyno:

 

[SG-1]

I have seen voltages in that range before on my service. I am the only one served by a 15KVA pole mounted transformer. When the voltage was high I had AM radio interference. The extra voltage would come & go. Then one day the transformer went out in a blaze of glory taking the TV with it. I think the primary winding was shorting out between turns & that was raising the secondary voltage.

 

[Smart $]

... I think the primary winding was shorting out between turns & that was raising the secondary voltage.

If it was shorting, when it was shorting it had the same effect as using lower-voltage primary tap.

 

[GoldDigger]

If it was shorting, when it was shorting it had the same effect as using lower-voltage primary tap.

As well as acting as a load and increasing the primary current.

 

[JoeTroubleShoot]

I can't speak to every utility, but I don't know any place that would let the voltage run that high on purpose. Maybe 130 when load is high. Like Meternerd said, it could be a regulator that is stuck or a self regulating step down that has the same problem. In my experience, regulators seem go to full raise when something happens to them. Same with the self regulating step downs which are sort of the same thing.

I've also seen plenty of single phase 120/240 transformers go bad all of the sudden and get high voltage. Easy for a troubleshooter to figure out whether it's that transformer that is bad or bad primary voltage from station, step-down, or regulator. Probably a good idea to call the company first.