Maximum voltage range

I have a piece of equipment that is rated for 575 VAC but is receiving 618v that fluctuates a bit for momentary instances at most from what I’ve seen. The piece of equipment is a large HVAC unit. The largest spike I’ve seen go to it was 633v (just barely over 10% of 575 v).

If I understand correct I can have a maximum of 10% deviation from the 575v rating but just wanted to make sure I had that correct.

Can someone please either confirm this if it’s correct or clarify if I’m misunderstanding an aspect of it somewhere?

Thanks.


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Hv&Lv

Senior Member
Location
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Occupation
Engineer/Technician
I’m assuming this is a 347/600 piece of equipment..
636 should be the upper limit of utilization voltage (6%)
632 would be the NEMA 10% upper limit.

is the transformer tapped? Can it be lowered a tap If so?
 
I’m assuming this is a 347/600 piece of equipment..
636 should be the upper limit of utilization voltage (6%)
632 would be the NEMA 10% upper limit.

is the transformer tapped? Can it be lowered a tap If so?
The tag on the HVAC unit says 575v.

I have a limited electrical ticket that allows me to work from the panel to the HVAC related equipment. Technically I can size and pull the wires and make the connections to a 600 amp HVAC unit from the panel, but replacing a light switch is beyond the allowable abilities of my ticketing qualifications (unless the light was mounted inside the HVAC unit or in some way related to the HVAC system itself, in which case it would be ok for me to then change that light switch). Re tapping a transformer is out of my tickets qualifications. I just want to know if it’s a concern for the voltage to be that high and if I should have a qualified electrician investigate further.

I wasn’t sure if the utilization voltage tolerance was calculated based off of 575v as the data tag specifies, or from 600v.

I will be on site agin tomorrow and should be able to get additional information if you tell me what you need.


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If anything, a slightly high voltage will allow the unit to rub at a slightly lower current.
That’s true. In theory the motor windings shouldn’t have an issue with it, and as long as I make sure the control voltage is maintained within its parameters then the control boards should be able to manage ok.... The electric heat would run hotter however and that could cause the elements to burn out prematurely... the humidifier lamps may also suffer from it as well.

As I think about it a little more It’s probably best to make sure it’s within designed parameters.


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synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Just to put your voltage measurements in the proper context, how was the HVAC equipment operating during these measurements?
For example, at a nominal expected load current, near the maximum rated load current, or perhaps even in the off condition?

It would also be good to confirm the measurements using more than one meter if you haven't already done so.
Also, a lot of meters are only specified up to 600VAC so that's something to be aware of.
 
Just to put your voltage measurements in the proper context, how was the HVAC equipment operating during these measurements?
For example, at a nominal expected load current, near the maximum rated load current, or perhaps even in the off condition?

It would also be good to confirm the measurements using more than one meter if you haven't already done so.
Also, a lot of meters are only specified up to 600VAC so that's something to be aware of.
The unit was powered on but commanded off while I was checking the voltages. So voltage was present at all the contractors and controls but the unit was not running.

Typically in my location the 575v equipment isn’t supplied by anything too far from that voltage so it surprised me a little to see it over 600v in this building.

I used two different fluke meters. Both are only rated for 600 so I’ll use the 289 when I go back tomorrow. I just don’t carry that one in my bag with me all the time.



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I’m assuming this is a 347/600 piece of equipment..
636 should be the upper limit of utilization voltage (6%)
632 would be the NEMA 10% upper limit.

is the transformer tapped? Can it be lowered a tap If so?
As far as the 347/600 assumption, I’m guessing that is what we have here also. I’ll see if I can get access to the electrical room tomorrow.

Sorry if I’m getting my terminology mixed up here, I’m trying my best to understand...
I typically see 575v at equipment. Is 575v just a utilization voltage (voltage being supplied by the last transformer on route to the equipment?) and not a distribution voltage? (Voltage being supplied by the buildings main transformer?) Would they be pulling these wires directly from the buildings main distribution transformer? (Well... from a panel that is supplied directly from the main distribution transformer?)

I’m trying to figure out why they wouldn’t have stepped it down to 575v for this equipment, or if it really matters. I hear some people say that 575v and 600v are basically the same thing.... maybe I’m overthinking it, but then you start creeping up on the voltage from 600v and it starts to become a problem a little bit quicker than if it was supplied at 575v

Please remember I don’t see what goes on behind the panel very often so if I sound a little confused it’s probably because I am. I don’t want to touch it, but if You can help me understand it then it will help me with troubleshooting and to make the right calls so I can get the right people in to fix it if there’s actually a problem worth addressing, and as I come across these in the future again as well.


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Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Take a look at these, see if they help clear some of the confusion.
it does get confusing when you have a motor that says 115V, a nominal that is 120V, an actual voltage of 124V, with limits that say as high as 126V
if there are taps at the transformer it can be lowered a bit.
 

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kwired

Electron manager
Location
NE Nebraska
I believe you probably have a system with a nominal voltage of 600. Distribution tolerance of 5% is probably acceptable.

Here your unit would probably be a 460 volt unit, per nameplate. Distribution volts would nominally be 480. Actual no load volts likely would be 495-500.

I think you are within allowed tolerances.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
NEMA standards are what utilization equipment is built to, so motors would fall under this. ANSI standards call for the Utilization Voltage to be purposely lower than the Distribution Voltage, assuming there will be voltage drop from the Service Entrance to the motor connection, so a motor rated for 575V is INTENDED for a 600V distribution system. NEMA MG-1 for motors calls for a tolerance of +-10% of nameplate rated voltage so a 575V motor would be OK with up to 632.5V.

Distribution Voltage levels are set by the utilities that generate it, but for the most part they also follow ANSI standards that call for a tolerance of +-5% maximum. So a 600V distribution system can get as high as 630V, which if compared to the NEMA standard means you have a slight buffer.

618V is well within both tolerance bands. 633V is outside of them both, but is not so far out of the NEMA design standard that I would be worried about it if the spikes are brief.
 
NEMA standards are what utilization equipment is built to, so motors would fall under this. ANSI standards call for the Utilization Voltage to be purposely lower than the Distribution Voltage, assuming there will be voltage drop from the Service Entrance to the motor connection, so a motor rated for 575V is INTENDED for a 600V distribution system. NEMA MG-1 for motors calls for a tolerance of +-10% of nameplate rated voltage so a 575V motor would be OK with up to 632.5V.

Distribution Voltage levels are set by the utilities that generate it, but for the most part they also follow ANSI standards that call for a tolerance of +-5% maximum. So a 600V distribution system can get as high as 630V, which if compared to the NEMA standard means you have a slight buffer.

618V is well within both tolerance bands. 633V is outside of them both, but is not so far out of the NEMA design standard that I would be worried about it if the spikes are brief.
The spikes were only very brief. It sounds like it’s not a concern. Thanks for the replies everyone!


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