Over Voltage Issues

Ambient44

Member
Location
Oak Lawn, IL
We are having over voltage issues with a few RTU's on a building we service, the voltage at the unit is 498V Phase to phase, the Carrier Unit nameplate says it is rated for 460V, of which we typically allow 5%+/- which would put us at 483V max.
They are blowing circuit boards often and the manufacturer says this over-voltage issue is the cause.
We contacted the utility company to turn the voltage down but it affected to many surrounding companies so they could not maintain the voltage to the lower setting.
My question is what is the best most reasonable to the customer solution to regulating the voltage to the units?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
You may need to go back to Carrier.
In the US the utilities are allowed to supply a nominal 480V +/- 5% for a range of 456V to 504V. Your utility fits into this range.
Most US manufacturers use a utilization voltage of 460V +/- 10%, for a range of 414V to 506V. Notice how this compare to the utility supply range?

The reason manufacturers use a lower utilization voltage, with a wider tolerance, is to accommodate the various voltages found in a facility, due to the proximity to the service entrance and potential voltage drops for remote equipment.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If it is just the PC boards that are failing, you may want to look at the Power Supply that provides the control power to the boards, it may have a setting to adjust for the proper voltage output. It may also be defective.
 

Ambient44

Member
Location
Oak Lawn, IL
You may need to go back to Carrier.
In the US the utilities are allowed to supply a nominal 480V +/- 5% for a range of 456V to 504V. Your utility fits into this range.
Most US manufacturers use a utilization voltage of 460V +/- 10%, for a range of 414V to 506V. Notice how this compare to the utility supply range?

The reason manufacturers use a lower utilization voltage, with a wider tolerance, is to accommodate the various voltages found in a facility, due to the proximity to the service entrance and potential voltage drops for remote equipment.

Jim,

You mentioned the above standards for "most US manufacturers", I was wondering if there was a written rule they follow and if you know where to find that. It would be useful in dealing with Carrier to have something in writing that I could present to them since they are saying the voltage level is the source of the problem with their units.

Thank you
Tom
 

Ambient44

Member
Location
Oak Lawn, IL
If it is just the PC boards that are failing, you may want to look at the Power Supply that provides the control power to the boards, it may have a setting to adjust for the proper voltage output. It may also be defective.
Jreaf,

I am getting thrown into the mix after the fact, I was just going off of what the HVAC tech told me so I do not know the actual components that have burned out due tot he over voltage except to say they mentioned a board, a transformer and other controller components. If we are called back out I will check with them but I will leave the internal diagnostics to them and deal with their incoming voltage issues.

This is a pretty large facility with (4) RTU's on it, they have issues with each individual unit at times and once all at once. So ther is something going on. I was going to try a surge suppressor on one of the units to see if it makes any difference compared to the ones without surge suppressors. Problem is the stock on surge suppressors is "Suppressed" at this time....lol

Thanks for your input
Tom
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Jim,

You mentioned the above standards for "most US manufacturers", I was wondering if there was a written rule they follow and if you know where to find that. It would be useful in dealing with Carrier to have something in writing that I could present to them since they are saying the voltage level is the source of the problem with their units.

Thank you
Tom
I would think it would be in the UL standard or something from the HVAC industry.
Per the NEC the nominal supply voltage is 480V, Doesn't Carrier expect their products to be installed per the NEC?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
This is a pretty large facility with (4) RTU's on it, they have issues with each individual unit at times and once all at once.
Is it possible you have units with some internal 'component incompatibility'? You probably got them all from one manufacturing batch so vendor problem would likely be common to them all.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
This is a pretty large facility with (4) RTU's on it, they have issues with each individual unit at times and once all at once. So there is something going on. I was going to try a surge suppressor on one of the units to see if it makes any difference compared to the ones without surge suppressors. Problem is the stock on surge suppressors is "Suppressed" at this time....lol

That does sound like a surge or sustained overvoltage might've caused the failures.
Are there power factor correction capacitors on the 480V service or feeder? If so then perhaps they are too large for the inductive load on them (for example, when motor loads are shut off) which then results in an overvoltage. Just speculating ...
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
That does sound like a surge or sustained overvoltage might've caused the failures.
Sounds like power quality monitoring is in order at this point.

I was just going off of what the HVAC tech told me...

Which is another problem. He may know his business but for power problems he's in the dark.
It would be useful in dealing with Carrier...
Are you going to contact Carrier directly or are you going to let the HVAC tech tell them what he thinks?

-Hal
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
We are having over voltage issues with a few RTU's on a building we service, the voltage at the unit is 498V Phase to phase, the Carrier Unit nameplate says it is rated for 460V, of which we typically allow 5%+/- which would put us at 483V max.
They are blowing circuit boards often and the manufacturer says this over-voltage issue is the cause.
We contacted the utility company to turn the voltage down but it affected to many surrounding companies so they could not maintain the voltage to the lower setting.
My question is what is the best most reasonable to the customer solution to regulating the voltage to the units?
Check out page 9.
It may not be the exact same unit but it’s carriers specs.
Says it goes to 506V.
You need HVAC advice, go with the HVAC guy.
You need electrical advice, the HVAC guy is the wrong person to be giving that advice or opinion.
 

drktmplr12

Senior Member
Location
South Florida
Occupation
Electrical Engineer
you have a dranetz PQ meter or logger?

if no, might want to consider hiring a third party testing co to come hook one up if you are spending 1000's on replacement parts already
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Wouldn’t doubt the POCO would have one and MAY do it if you talk to someone in engineering, not a call center.

I have connected ours for our customers just to check issues.
 
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