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So I encountered a 3 phase panel where phase 1 to g was 156v and the other 2 phases were 134v to ground. No neutral. 236 v phase to phase. I hooked up 208 v heaters. Can anyone explain this issue?
 

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This is an 240 volt 3∆ 3 wire ungrounded system.

The odd phase to ground voltages were the result of capacitive coupling. If you were to read them with a solenoid type tester (or anything else that loads the circuit) the reading would be 0.

There is no 120 with this system, 240 only.
 

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micromind said:
If they're 240 volt, very likely a long time. The fact that the system is ungrounded doesn't matter to a heater.
If 240 then true. But he stated 208 volt heaters.
 

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This is an 240 volt 3∆ 3 wire ungrounded system.

The odd phase to ground voltages were the result of capacitive coupling. If you were to read them with a solenoid type tester (or anything else that loads the circuit) the reading would be 0.

There is no 120 with this system, 240 only.
Winner winner chicken dinner with a good bottle of wine.
 

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This is an 240 volt 3∆ 3 wire ungrounded system.

The odd phase to ground voltages were the result of capacitive coupling. If you were to read them with a solenoid type tester (or anything else that loads the circuit) the reading would be 0.

There is no 120 with this system, 240 only.
So help the apprentice out with some theory . . .

Are the different voltages to ground because of the loads between each leg aren't perfectly balanced? And because the system is not grounded (and has a reference point), it causes the phase to ground voltages to fluctuate?

I was taught that systems are grounded to maintain a common reference point so that the voltages don't fluctuate depending on the load. Well that's one of the reasons. Also to dissapate surges and lightning strikes. I'm just trying to get this all in perspective. Am I right/wrong in my assumptions?
 

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Are the different voltages to ground because of the loads between each leg aren't perfectly balanced? And because the system is not grounded (and has a reference point), it causes the phase to ground voltages to fluctuate?
That is correct. In an unearthed system you do not have any physical connection to the mass of earth, however you are still earthed mainly through distributed capacitance of the system. This means if your three phase system is balance(the load on each phase is the same), the capacitive coupled current flowing between each phase and earth would sum to zero, effectively holding your neutral point of the system at earth potential. So if I measured the line to earth voltages in a balanced system they would be equal to your line to neutral voltage.

But as the load on each phase changes this current no longer sums to zero at the earth point. This shifts the neutral point of the system, so your line to earth voltages will also reflect this.

In a solidly earthed system your line to earth voltages do not change as the system becomes more unbalanced.

I was taught that systems are grounded to maintain a common reference point so that the voltages don't fluctuate depending on the load. Well that's one of the reasons. Also to dissapate surges and lightning strikes. I'm just trying to get this all in perspective. Am I right/wrong in my assumptions?
Line to earth overvoltages brought on by earth faults, distributed capacitance and lightning is the main draw back to unearthed systems.

Ummmm....I got a really good article on unearthed systems on my computer, but can't seem to upload it due to the file being to large.:(
 

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How long do you think those heaters will last?

Most are dual 208/240 rated. Most.





That is correct. In an unearthed system you do not have any physical connection to the mass of earth, however you are still earthed mainly through distributed capacitance of the system. This means if your three phase system is balance(the load on each phase is the same), the capacitive coupled current flowing between each phase and earth would sum to zero, effectively holding your neutral point of the system at earth potential. So if I measured the line to earth voltages in a balanced system they would be equal to your line to neutral voltage.

But as the load on each phase changes this current no longer sums to zero at the earth point. This shifts the neutral point of the system, so your line to earth voltages will also reflect this.

In a solidly earthed system your line to earth voltages do not change as the system becomes more unbalanced.



Line to earth overvoltages brought on by earth faults, distributed capacitance and lightning is the main draw back to unearthed systems.

Ummmm....I got a really good article on unearthed systems on my computer, but can't seem to upload it due to the file being to large.:(
Pm or Email It if you can. Ive been looking for a good doc on ungrounded systems.
 
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