We have a situation where a customer is using 120/208v 3? 4wire rated service entrance equipment which will be connected to a 240v 3? 3wire corner grounded closed delta utility supply. Terminating A? and C? to their associated bus, B? to the ?neutral? bus which grounds the service and not using B? bus. Now you have 240v to ground on two of the three phases and 240v phase to phase of the equipment which is only labeled for 120v to ground, 208v phase to phase. This equipment will work but doesn?t need to be listed for such use? Does NEC touch base on voltage ratings? Appreciate any assistance.
Supply Voltage vs. Equipment Ratings
- Thread starter Utymtr
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- Bremerton, Washington
- Occupation
- Master Electrician
For three phase we are only concerned with the phase to phase, not phase to ground.
The NEC has two clear rules on use of (for example) 200 volt motors on 230 systems, 230 volt motors on 200 volt systems, and that is you can't do it.
110.3(B)
110.4
The panel would have to be listed for a delta application (as the voltage to ground exceeds the slash rating of a 120/208)
The NEC has two clear rules on use of (for example) 200 volt motors on 230 systems, 230 volt motors on 200 volt systems, and that is you can't do it.
110.3(B)
110.4
The panel would have to be listed for a delta application (as the voltage to ground exceeds the slash rating of a 120/208)
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
OCPD may be 'slash' rated or 'straight' rated. A 'slash' rated breaker is one that has a lower line-ground voltage rating then its line-line voltage rating.
I very much doubt that the breakers in this panel are rated for 208V. It is far more likely that they are 'slash' rated with a line-line rating of 240V _and_ a line-ground rating of 120V. Remember that during a line-ground fault, a single breaker is expected to clear the fault, but in a line-line fault, there are _two_ breakers in series operating to clear the fault.
For a 240V corner grounded delta, you need breakers and equipment with a 240V straight rating.
-Jon
I very much doubt that the breakers in this panel are rated for 208V. It is far more likely that they are 'slash' rated with a line-line rating of 240V _and_ a line-ground rating of 120V. Remember that during a line-ground fault, a single breaker is expected to clear the fault, but in a line-line fault, there are _two_ breakers in series operating to clear the fault.
For a 240V corner grounded delta, you need breakers and equipment with a 240V straight rating.
-Jon
I should have noted that the equipment is a meter-stack rated 120/208v 4 wire connected to 240v 3 wire corner grounded delta, no main and four outgoing positions. 110.3 and 110.4 are examples I was looking for in NEC. Again, the equipment is not listed for such use but, I feel by ignorance, has been approved by AHJ. It seems that 240.85 also fit the bill for what I've originally was looking for, documentation... Any further comments would be appreciated!
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