# How much above nominal 120 volts is too much?



## 51360 (Jun 9, 2014)

Very seldom have I seen nominal 120 volts much above 120v. 

I recently did a service call in a RV park, and the incoming voltage at the RV receptacle was 126 volts. Normally not a big deal, but this RV unit had a Prosine inverter/charger unit that would not transfer over to shore power, ( campsite power ), at that voltage.

The default setting was 130 volts, and the unit was displaying 131 volts, when I was reading 126 volts with a pretty reliable meter. So that's one issue.

I told the camper that once the site gets busier, the voltage will likely drop and his unit will work fine. I didn't recommend changing the default voltage.

Today he returned from a long weekend boondocking adventure, and I plugged him in and his Prosine unit was reading 129 volts, and all was fine. I was reading 125 volts.

My question is this, at what point should the site owners inform Fortis? They are within 5%, so I say ok. As the site fills up, all will be good.

Borgi


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## dmxtothemax (Jun 15, 2010)

Like you said, it is still within spec.
But if you ask them nicely, 
Then they MAY be able to adjust,
Can not hurt to ask !
But do it politely !


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## macmikeman (Jan 23, 2007)

Ten per cent plus or minus for motors. 11 per cent is too high, so once you get above ten you will start harming motors, and more the merrier.


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## Electric_Light (Apr 6, 2010)

The courtesy volt meter having an error range of +/- 2-3% doesn't surprise me. 
What's your DMMs model and what's the accuracy specs? 
If the inverter trip point is off, raise the setting to compensate for it so the real trip point is 132v or so. 

Service voltage of 120 +/- 5% is the guideline. If it's reading 125v now, it could read lower under other customer load.


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## Meadow (Jan 14, 2011)

Is this near a substation? Not uncommon when customers are at the beginning of a distribution feeder.


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## Jhellwig (Jun 18, 2014)

I know around here my power company does not like it when it gets over or really close to 125 volts.


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## 51360 (Jun 9, 2014)

meadow said:


> Is this near a substation? Not uncommon when customers are at the beginning of a distribution feeder.


Not sure meadow, the generating plant is within 50 km, but not sure where the sub is. The customer has more than one transformer, the campsite transformer is the only one above nominal.

The actual RV receptacle is within 30 ft. of the panel, so no voltage drop at all.

I don't want to deal with the utility company if it's a non issue.

Borgi


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## Meadow (Jan 14, 2011)

Borgi said:


> Not sure meadow, the generating plant is within 50 km, but not sure where the sub is. The customer has more than one transformer, the campsite transformer is the only one above nominal.
> 
> The actual RV receptacle is within 30 ft. of the panel, so no voltage drop at all.
> 
> ...


If just that one transformer is over the Taps may be set to high.


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## 51360 (Jun 9, 2014)

meadow said:


> If just that one transformer is over the Taps may be set too high.


I can take pictures, but I am not sure if there are taps. They are pole mounted transformers. :001_huh: 

But, I am not knowing. 

Borgi


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## Meadow (Jan 14, 2011)

Borgi said:


> I can take pictures, but I am not sure if there are taps. They are pole mounted transformers. :001_huh:
> 
> But, I am not knowing.
> 
> Borgi




Some pole pigs do have taps, either that the feed for the trailer is coming off a different line.

What voltage do you get from the other transformers?


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## 51360 (Jun 9, 2014)

meadow said:


> Some pole pigs do have taps, either that the feed for the trailer is coming off a different line.
> 
> *What voltage do you get from the other transformers*?


~ 115-118 volts.

Borgi


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## Meadow (Jan 14, 2011)

Borgi said:


> ~ 115-118 volts.
> 
> Borgi


Id say improper taps (either left to high or to low) or one of the POCO's phases is higher than the other two for various abnormal reasons. 

My gut is on the transformer, and IMO worth calling the POCO. You could always tell them 'I am getting voltages over of 127 volts at certain times' which might be true considering you never measured the full 24 hour bandwidth.


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## Bad Electrician (May 20, 2014)

dmxtothemax said:


> Like you said, it is still within spec.
> But if you ask them nicely,
> Then they MAY be able to adjust,
> Can not hurt to ask !
> But do it politely !


Our local utilities do not have taps on their last transformers in line. So for them to adjust they affect everybody on the sub. Typically the subs are automatic tap changers.


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## Tiger (Jan 3, 2008)

127V seems perfect to me. As the load increases the voltage will drop toward 120.


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## Bad Electrician (May 20, 2014)

Tiger said:


> 127V seems perfect to me. As the load increases the voltage will drop toward 120.


There are a lot of factors to get it to drop to 120 from 127 and not something I would count on.


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## 51360 (Jun 9, 2014)

Today is a good day to head over to the campsite and do some quick measurements. Most of the seasonals will be there, air on and fridges running.

I suspect the RV with the Prosine unit is still running fine, and the voltage is a wee bit lower.

Best to test the voltages first, then the fridge. 

Borgi


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## Jhellwig (Jun 18, 2014)

Borgi said:


> I can take pictures, but I am not sure if there are taps. They are pole mounted transformers. :001_huh:
> 
> But, I am not knowing.
> 
> Borgi


I bet there are some that don't but most do. They might not be externaly changeable though. They might have to take the top off to change them.


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## KDC (Oct 19, 2012)

Our line regulators are usually set to 123.5V +/- 1.5V at the regulator, and it will buck/boost to maintain that. So houses nearest the regulators can see between 122 to 125V, then as you get farther you get line drop and the voltage. 

Sounds like in this case there may not be a regulator involved, and the line is normally loaded down, so they changed the transformer trap (external or internal) to compensate

Or the regulator in question is screwed, which happens.


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## 51360 (Jun 9, 2014)

KDC said:


> Our line regulators are usually set to 123.5V +/- 1.5V at the regulator, and it will buck/boost to maintain that. So houses nearest the regulators can see between 122 to 125V, then as you get farther you get line drop and the voltage.
> 
> *Sounds like in this case there may not be a regulator involved, *and the line is normally loaded down, so they changed the transformer trap (external or internal) to compensate
> 
> Or the regulator in question is screwed, which happens.


Ok, so would I be able to see it from the ground? I have a picture of the transformer somewhere.

I just returned from there and the voltages are more normal, closer to nominal. It's 25 ° C here today, and most of the campers are there. The RV with the Prosine is displaying 124 volts and working fine, I measure 119 volts at his site, and 118 volts at sites furthest away from the panel.

The RV owner said his unit switched over in the middle of the night, but returned to site power in the morning. We are all ok with that,

I don't see a need to get Fortis, ( utility company ) involved, but I may call for information just out of curiousity! 

Thanks for your input everyone. :thumbsup:

Borgi


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## 51360 (Jun 9, 2014)

Electric_Light said:


> The courtesy volt meter having an error range of +/- 2-3% doesn't surprise me.
> What's your DMMs model and what's the accuracy specs?
> *If the inverter trip point is off, raise the setting to compensate for it so the real trip point is 132v or so. *
> 
> Service voltage of 120 +/- 5% is the guideline. If it's reading 125v now, it could read lower under other customer load.


Missed this last night, sorry for not answering.

I have an RCC 360 digital multimeter, it's older and I can't find the specs. I agree, my measurements could be off a wee bit also.

I contacted a Prosine service rep via e mail and he said I could raise the default to a maximum 135 volts, but he was concerned about the other loads. The Prosine can handle it fine. So I asked if I could calibrate the measurement, and he said no.

After testing today, I will not bother changing the settings.

Borgi


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## KDC (Oct 19, 2012)

Borgi said:


> Ok, so would I be able to see it from the ground? I have a picture of the transformer somewhere.


A regulator is an auto transformer, a separate piece of equipment, you'd have to trace the primary back towards the switchyard. They can be pole mount or pad mount, and to the untrained eye could be mistaken for a polemount transformer. 

They have an attached controller that uses a PT to measure the primary voltage, and send step commands to keep the voltage within it's set range. 
(We tend to use cooper ones like these)


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## 51360 (Jun 9, 2014)

KDC said:


> A regulator is an auto transformer, a separate piece of equipment, you'd have to trace the primary back towards the switchyard. They can be pole mount or pad mount, and to the untrained eye could be mistaken for a polemount transformer.
> 
> They have an attached controller that uses a PT to measure the primary voltage, and send step commands to keep the voltage within it's set range.
> (We tend to use cooper ones like these)


Thanks, good to know. There is definitely a pole mount transformer on the property, within 50 ft. of the main service entrance. It only feeds the campground.

I will have a look further upstream, but nothing like that on the property, or within sight of the property. 

Borgi


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## Meadow (Jan 14, 2011)

Also of note a defective capacitor bank can cause that (one the isn't switching off line under higher voltages/leading power factor)


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## Meadow (Jan 14, 2011)

Borgi said:


> Thanks, good to know. There is definitely a pole mount transformer on the property, within 50 ft. of the main service entrance. It only feeds the campground.
> 
> I will have a look further upstream, but nothing like that on the property, or within sight of the property.
> 
> Borgi


Follow the line out, it may be some distance away. If you want you can PM me with a location and I can see if I can follow it out on Google earth.


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## Electric_Light (Apr 6, 2010)

Borgi said:


> Ok, so would I be able to see it from the ground? I have a picture of the transformer somewhere.
> 
> I just returned from there and the voltages are more normal, closer to nominal. It's 25 ° C here today, and most of the campers are there. The RV with the Prosine is displaying 124 volts and working fine, I measure 119 volts at his site, and 118 volts at sites furthest away from the panel.
> 
> ...


I would get a mid range or better Fluke meter (not the budget one). I trust them for their calibration stability. The specs for 87V is ±(0.7% + 2 digit) 
So, this means that if the 87V reads 120.0v, the actual voltage can be anywhere between 119 to 121v. 

There are plenty of field grade meters with worse accuracies. Plus or minus means you could actually have real voltage of 121v and your meter reading 119v and inverter's courtesy gauge reading 124v. 

The voltage meter on my APC UPS and my Fluke don't really agree either. Nothing I could do other than pushing the limit settings around.


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## 51360 (Jun 9, 2014)

Electric_Light said:


> *I would get a mid range or better Fluke meter (not the budget one).* I trust them for their calibration stability. The specs for 87V is ±(0.7% + 2 digit)
> So, this means that if the 87V reads 120.0v, the actual voltage can be anywhere between 119 to 121v.
> 
> There are plenty of field grade meters with worse accuracies. Plus or minus means you could actually have real voltage of 121v and your meter reading 119v and inverter's courtesy gauge reading 124v.
> ...


When I bought my meter over 20 years ago, it was not a budget meter. :laughing: It has served me well, and is as accurate as I need. I have used pricy Fluke meters supplied by the employer, and mine was as accurate as the Fluke. So, if it's not broke, don't fix it.

My next purchase will be a Fluke, but likely a combination meter and insulation tester. 

In this case it didn't matter, his Prosine unit was reading over 130 volts and shutting shore power down. Having an expensive Fluke meter would have made no difference. :thumbsup:

Now, if I was doing testing like Bad Electrician does, then that warrants expensive meters. 

Borgi


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## Electric_Light (Apr 6, 2010)

Borgi said:


> In this case it didn't matter, his Prosine unit was reading over 130 volts and shutting shore power down. Having an expensive Fluke meter would have made no difference. :thumbsup:
> 
> Now, if I was doing testing like Bad Electrician does, then that warrants expensive meters.
> 
> Borgi



It does if you suspect service voltage is out of NEMA specs, which is +/- 5%. 
If your meter allows +/- 2%, it makes it hard to figure out. 

The 289 is 0.3% + 0.25v over the rated temperature range. So, if your 289 registers 127v, then you know for certain that the voltage is within 126.37 to 127.63v. 

So, if you were to call about service voltage, just saying the model of your meter, and that it has a current calibration, you're less likely to get told that their service is within specs and PoCo blaming your meter might be reading high to avoid having to dispatch field service.

Right now, we don't know what the real voltage is. Your meter could be reading on the low side, and the inverter could be reading on the high side and this tend to increase the perceived deviation whereas if they were both skewed in the same direction, it creates a perception of accuracy.


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## chicken steve (Mar 22, 2011)

Bad Electrician said:


> Our local utilities do not have taps on their last transformers in line. So for them to adjust they affect everybody on the sub. Typically the subs are automatic tap changers.


Which brings to mind one serv call, fused disco's blowing compressors in building A , with building B & C calling for similar problems shortly afterwards

Fix-poco sub auto-taps , which wean voltage during peak, skipped a tap on the way down....

~CS~


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## 51360 (Jun 9, 2014)

Electric_Light said:


> It does if you suspect service voltage is out of NEMA specs, which is +/- 5%.
> If your meter allows +/- 2%, it makes it hard to figure out.
> 
> The 289 is 0.3% + 0.25v over the rated temperature range. So, if your 289 registers 127v, then you know for certain that the voltage is within 126.37 to 127.63v.
> ...


Exactly why I didn't get Fortis involved! My meter is fine!

Having an expensive Fluke meter would *NOT* have made any difference to them either. If I did manage to get through the layers of idiots first.

Borgi


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