High voltage question

[rbum]

I am a maintenance electrician and I have a 277/480 volt ungrounded system feeding some ball park lights.It seems very weird to have some weird voltages such as i have there. From the utility company I have at the main phase A 519 v to ground, phase B 323 v to ground, phase C 208v to ground, between Phases A&B 482v, B&C 490 v A&C 485 v. Is this normal for a ungrounded system.

Please tell me more about this.

 

[BAHTAH]

Ungrounded?

Ungrounded?

I am a maintenance electrician and I have a 277/480 volt ungrounded system feeding some ball park lights.It seems very weird to have some weird voltages such as i have there. From the utility company I have at the main phase A 519 v to ground, phase B 323 v to ground, phase C 208v to ground, between Phases A&B 482v, B&C 490 v A&C 485 v. Is this normal for a ungrounded system.

Please tell me more about this.

If in fact you have a 480/277Y system, the center tap of that transformer should be grounded at the pole or utility pad as well as the neutral being grounded at the service. If the circuits supplying the lighting is 480V 3ph there should have been a ground installed with those circuits out to the poles and you should be reading 277V to ground from each phase to the equipment grounding conductor. If you have a 480/277Y service from the utility I would be looking for an open neutral back to the utility transformer since that is your only solid connection to the transformer center tap. The earth does not make a good conductor.

 

[zog]

You got me all excited with the high voltage title, but this is still low voltage. 1st thing we need to know, is this a 480/277 or an ungrounded system? Your 1st statement contridicts itself.

 

[LarryFine]

This sounds line an ungrounded Delta to me. A quick look at the transformer bank would tell you, if you know what to look for.

 

[winnie]

Those voltages are perfectly normal for an ungrounded system. The reason is that in an ungrounded system you do not have a good solid earth reference to 'tie' the voltages to specific values relative to ground. In an ungrounded system, the voltage to ground are influenced by any tiny connection made to ground, including the connection made by the meter itself. If you used a 'low impedance' volt meter, you would see very different numbers.

With that said, the cautions you are seeing in the other posts are extremely important. NEC prohibits any system that uses a neutral from being ungrounded, and 480/277V implies that you have a neutral. Do you really have a 480V ungrounded system, or do you really have a 480/277V broken system

Note: I believe that you _can_ use a 480/277V transformer to supply a 480V ungrounded system, as long as the neutral is never grounded and never taken out of the transformer.

-Jon

 

[rbum]

Those voltages are perfectly normal for an ungrounded system. The reason is that in an ungrounded system you do not have a good solid earth reference to 'tie' the voltages to specific values relative to ground. In an ungrounded system, the voltage to ground are influenced by any tiny connection made to ground, including the connection made by the meter itself. If you used a 'low impedance' volt meter, you would see very different numbers.

With that said, the cautions you are seeing in the other posts are extremely important. NEC prohibits any system that uses a neutral from being ungrounded, and 480/277V implies that you have a neutral. Do you really have a 480V ungrounded system, or do you really have a 480/277V broken system

Note: I believe that you _can_ use a 480/277V transformer to supply a 480V ungrounded system, as long as the neutral is never grounded and never taken out of the transformer.

-Jon

Thank you for your reply. I think I am using the correct terminology.Ungrounded meaning i do not have a neutral at the main.At the pole I am unsure.I have had schooling on identifying pole connections in 1987 but i cannot recall that info. Does this make any sense?

 

[rbum]

This sounds line an ungrounded Delta to me. A quick look at the transformer bank would tell you, if you know what to look for.

are these uncommon readings I am getting? Yes there is no neutral at the main

 

[LarryFine]

are these uncommon readings I am getting? Yes there is no neutral at the main

They sound normal. With any Delta, only the line-to-line voltages are relevant. Loads do not care what the voltage to ground is, whether 1ph or 3ph.

With an ungrounded Delta, the voltage of each phase to ground will vary, dependent on the relative capacitance between each line and ground.

If you had a grounded Delta, you'd read 480, 480, and 0. You either have an intentionally-ungrounded Delta, or an unintentionally-ungrounded Delta.

 

[Power Tech]

If you have a 480/277 service and it is ungrounded.

You have some serious problems or you don't have 277V.

277V is 1, 480V "hot" with a neutral.

 

[brian john]

I have seen ungrounded systems designed by engineers, passed by the AHJ's and installed by professionals the transformers are 480Y/277 BUT, no neutral is utilized ANYWHERE in the system.

All lighting is fed from a SDS

 

[Power Tech]

Those voltages are perfectly normal for an ungrounded system. The reason is that in an ungrounded system you do not have a good solid earth reference to 'tie' the voltages to specific values relative to ground. In an ungrounded system, the voltage to ground are influenced by any tiny connection made to ground, including the connection made by the meter itself. If you used a 'low impedance' volt meter, you would see very different numbers.

With that said, the cautions you are seeing in the other posts are extremely important. NEC prohibits any system that uses a neutral from being ungrounded, and 480/277V implies that you have a neutral. Do you really have a 480V ungrounded system, or do you really have a 480/277V broken system

Note: I believe that you _can_ use a 480/277V transformer to supply a 480V ungrounded system, as long as the neutral is never grounded and never taken out of the transformer.

-Jon

Perhaps they did not bond or use the XO. Then there is no 277.

If a service is upgraded in this area it has to be 4 wire. POCO code.

 

[Smart $]

are these uncommon readings I am getting? Yes there is no neutral at the main

The line-to-line voltages are within accepted tolerance.

The line-to-ground voltages, if the system is ungrounded as it appears, are only important for detecting a ground faults. An ungrounded system as such is required to have a ground-faut detector.

 

[weressl]

I am a maintenance electrician and I have a 277/480 volt ungrounded system feeding some ball park lights.It seems very weird to have some weird voltages such as i have there. From the utility company I have at the main phase A 519 v to ground, phase B 323 v to ground, phase C 208v to ground, between Phases A&B 482v, B&C 490 v A&C 485 v. Is this normal for a ungrounded system.

Please tell me more about this.

It almost sounds like an ungrounded delta 480V system with a ground fault in one winding.