Building receiving 500V on a 480V service

[Machiavelli999]

A client, for whom my company often does work, asked me about an issue they are having. They have a major industrial campus and a group of their buildings receives measured voltage from the utility in the range of 495V-500V. This is on a nominally 480V service.

I have been around this campus for two years and I always have known that this was the case. I remember when I first joined, I questioned this and no one really seemed concerned.

Anyway, over the past couple years they have had some incidents that seem to tie back to this overvoltage situation. First, an elevator motor failed and the service repair guys blamed the voltage. Then an air compressor failed and service repair guys also blamed it on the voltage. They asked for my advice and I told them to ask the utility. But when they pushed back on the utility, the utility claimed the voltage delivered was within the approved tolerances. And I suppose 500V is only 4.2% above 480V.

BUT, I am just wondering if anyone has seen this before and if people think this is acceptable.

 

[ActionDave]

Not unusual to see 500V nominal. Not unusual for service guys to be wrong about what causes motor failures also.

 

[iceworm]

Yes, probably is. For example, scale down to 120V. 500V for a 480 service is 125V for the 120 level. Most would not consider that out of line. Still, one could call and ask the utility to turn down the tap changer one click. Your client sounds big enough they will have their own distribution transformer.

The utility should have published specs. If not call and ask. And if they aren't forth coming, call the state utility commission. They will have oversight and have access to the specs.

Occasionally the state utility commission is in bed with the utility. And then you are generally screwed (engineering definition please)

One other thing - check if the client has a bunch of pf correction on-line. That will drive the voltage up.

 

[LarryFine]

Motors tend to be constant-power loads, so they usually use less current on increased voltage, and thus usually run cooler, as the opposite is also true.

 

[Jraef]

Utility distribution voltage specifications call for +-5% of nominal. The utility is correct, they are well within their rights to deliver 500V for a 480V service.

Utilization voltage specifications (what equipment is supposed to be designed for) is +- 10%. The difference is deliberate.

If the elevator or compressor was getting 500V on a 460V rated motor, that is still within the expected tolerance for that motor design (up to 506V).
Telling someone that it's the fault of the utility is an easy cop-out.

 

[Hv&Lv]

 

[Hv&Lv]

1

 

[Cow]

I don't think your measured 500v is what is causing the issues.

But, that doesn't mean uneducated techs can't blame the voltage for their problems though....