Acceptable nominal voltage range

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Dsg319

Dsg319

Senior Member
Location
West Virginia
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Wv Master “lectrician”
Is there a certain percentage to go off of for accepting a voltage range compared to nominal voltage. For instance we done a small valve site consist of a 100 amp(240/120v) single phase service drop. And phase to phase voltage was in the 280’s (can’t remember exactly). I know motors and some other equipment can have a 10% tolerance. But I thought that was a little excessive.
 
Complicated subject. Lower voltages are often more tolerable than excessive voltages. It depends on the type of load. Yada yada yada.
The Idiots Guide to Voltage Tolerance Levels states +/- 10%. That seems to be a widely accepted basic norm, I think.
But the discussion definitely goes much, much deeper than that.

I agree with you and Tom that 280V is too high.
 
Dsg319 said:
Is there a certain percentage to go off of for accepting a voltage range compared to nominal voltage. For instance we done a small valve site consist of a 100 amp(240/120v) single phase service drop. And phase to phase voltage was in the 280’s (can’t remember exactly). I know motors and some other equipment can have a 10% tolerance. But I thought that was a little excessive.
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If it’s at 280 I would expect the transformer needs replacing. Sounds like an internal short between windings. Happens occasionally..
Call the POCO
 
Hv&Lv said:
If it’s at 280 I would expect the transformer needs replacing. Sounds like an internal short between windings. Happens occasionally..
Call the POCO
Click to expand...
The only thing is we have another site within a half mile and my supervisor said it was also high but not quite near as it was in the 260 range.
 
Dsg319 said:
The only thing is we have another site within a half mile and my supervisor said it was also high but not quite near as it was in the 260 range.
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Call the POCO. They may have a regulator that went rogue.
 
The ANSI standard for "Distribution Voltage" (meaning what the utility supplies), is 120/240V +-5%. So the upper limit would be 252V.

The ANSI standard for "Utilization Voltage" (what mfrs design to) on a 120/240V distribution voltage is 115/230V +-10%, so the upper limit would be 253V.

280V is too high no matter how you look at it. Is this the Utility sourced voltage, or do you have your own transformer making it? If it's from the utility, they need to be called to fix it. If it's your own transformer, look for some taps. Someone may have adjusted the taps when there was a large load causing a voltage drop, now that load is gone, so it needed to be put back down and wasn't. Happens a lot.
 
Jraef said:
The ANSI standard for "Distribution Voltage" (meaning what the utility supplies), is 120/240V +-5%. So the upper limit would be 252V.

The ANSI standard for "Utilization Voltage" (what mfrs design to) on a 120/240V distribution voltage is 115/230V +-10%, so the upper limit would be 253V.

280V is too high no matter how you look at it. Is this the Utility sourced voltage, or do you have your own transformer making it? If it's from the utility, they need to be called to fix it.
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It’s the POCO,S transformer. My supervisor told our on on-site electrical inspector about the situation.

Personally if it was me i would push hard to have someone contacted. Not sure the measures that are being taken for that. Over my head now, done what I could and told my supervisor I reached out and found that the supplied voltage, isn’t right and shouldn’t be acceptable.

At the time I was around the inspector he didn’t seemed surprised really , so I didn’t doubt him seeing he is older(more electrical experience) and really I believe he is a brilliant man, but I just didn’t figure it could be right. So I came here and researched.
 
Dsg319 said:
It’s the POCO,S transformer. My supervisor told our on on-site electrical inspector about the situation.

Personally if it was me i would push hard to have someone contacted. Not sure the measures that are being taken for that. Over my head now, done what I could and told my supervisor I reached out and found that the supplied voltage, isn’t right and shouldn’t be acceptable.

At the time I was around the inspector he didn’t seemed surprised really , so I didn’t doubt him seeing he is older(more electrical experience) and really I believe he is a brilliant man, but I just didn’t figure it could be right. So I came here and researched.
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You have done what you can do.
Too bad you report to people that apparently have no sense of responsibility or care about their company or their position in that company.

what will happen is someone else on the POCO line will call the POCO, the problem will be fixed and your “brilliant” supervisor will then assume you blew everything out of proportion.
 
Dsg319 said:
Is there a certain percentage to go off of for accepting a voltage range compared to nominal voltage. For instance we done a small valve site consist of a 100 amp(240/120v) single phase service drop. And phase to phase voltage was in the 280’s (can’t remember exactly). I know motors and some other equipment can have a 10% tolerance. But I thought that was a little excessive.
Click to expand...
Just had a kaboom moment and remembered (I think) the exact voltage. 278/139v
 
Standard for transformers is taps at -5%, -2.5%, 0, +2.5%, +5%. NEMA tolerances on most standard equipment is +10/-15%. Motors are +/-10%. ANSI gives standard voltages with generally -5% for utilization so set transformer to 120 V but equipment is designed for 110-115 V (there is some variation) or multiples. So at 480 V at the transformer the motor will be 460 V. CBEMA has higher limits for temporary conditions like starting a large motor but with strict time limits. Most electronics rides through CBEMA limits.
 
If the ANSI and CBEMA standards seem “old” that’s ok...think of the consequences if we obsoleted voltage requirements. I shudder to think of Elon Musk writing power distribution specs.
 
Hv&Lv said:
If it’s at 280 I would expect the transformer needs replacing. Sounds like an internal short between windings. Happens occasionally..
Call the POCO
Click to expand...


How long will the pole pig hold? I'm under the impression that shorted winding will carry a lot of circulating current.
 
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