230.95 GF protection of Equipment 480/277 only?

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johnnydn

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Oakland, CA
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Junior Electrical Design Engineer
I am having trouble interpreting the code which requires GF protection on service disconnects. I've read from different online resources that this is only a requirement for 480/277V but not 120/208V systems. My confusion is where does the code delineate which voltage systems are applicable and which are not? Does the Utility (CA in my case) have special exceptions which trigger this 480/277V only or is there a code section that articulates this delineation?

Taken from 2017 NEC:
230.95 Ground-Fault Protection of Equipment.
Ground-fault protection of equipment shall be provided for solidly grounded wye electric services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase for each service disconnect rated 1000 amperes or more. The grounded conductor for the solidly grounded wye system shall be connected directly to ground through a grounding electrode system, as specified in 250.50, without inserting any resistor or impedance device.

The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.
 
johnnydn said:
I am having trouble interpreting the code which requires GF protection on service disconnects. I've read from different online resources that this is only a requirement for 480/277V but not 120/208V systems. My confusion is where does the code delineate which voltage systems are applicable and which are not? Does the Utility (CA in my case) have special exceptions which trigger this 480/277V only or is there a code section that articulates this delineation?

Taken from 2017 NEC:
230.95 Ground-Fault Protection of Equipment.
Ground-fault protection of equipment shall be provided for solidly grounded wye electric services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase for each service disconnect rated 1000 amperes or more. The grounded conductor for the solidly grounded wye system shall be connected directly to ground through a grounding electrode system, as specified in 250.50, without inserting any resistor or impedance device.

The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.
Click to expand...
The only commonly used voltage system in the US that meets the requirement in 230.95 is a 480Y/277 volt system. There are also some 600Y/347 volt systems that would require this same ground fault protection but they are not near as common as the 480 volt system.

The 208Y/120 volts system does not qualify as the voltage to ground does not exceed 150 volts.

It also does not apply to the 240/120 volt 4 wire delta, even though the voltage to ground on one leg exceeds 150 volts to ground, because the rule only applies to wye systems.
 
The NEC does not explain the rules. For that you would need to research the documentation when the change was done, or understand electrical theory, or ask here.
277 ground faults won’t burn clear and the arc won’t self extinguish like a 120 fault will. Due to fires with 277 volt systems in the 70 ‘s gfpe rules were added
 
tom baker said:
The NEC does not explain the rules. For that you would need to research the documentation when the change was done, or understand electrical theory, or ask here.
277 ground faults won’t burn clear and the arc won’t self extinguish like a 120 fault will. Due to fires with 277 volt systems in the 70 ‘s gfpe rules were added
Click to expand...
And typically will not draw enough current, because of the impedance of the arc, to trip the OCPD.
 
tom baker said:
277 ground faults won’t burn clear and the arc won’t self extinguish like a 120 fault will. Due to fires with 277 volt systems in the 70 ‘s gfpe rules were added
Click to expand...
I've seen many incidents where 277 to ground either caused or nearly caused a fire even though on less than 1000 amp supply.

Then about a quarter century ago the code making geniuses decided we need AFCI protection on 120 volts to ground in many locations even though it does not sustain arcing without some external help:unsure:
 
kwired said:
I've seen many incidents where 277 to ground either caused or nearly caused a fire even though on less than 1000 amp supply.

Then about a quarter century ago the code making geniuses decided we need AFCI protection on 120 volts to ground in many locations even though it does not sustain arcing without some external help:unsure:
Click to expand...
I was going to submit a PI to delete 210.12 with the substantiation being that 230.95 tells us that self-sustaining arcs do not exist at 120 volts to ground, but since it would be rejected, I did not submit.
 
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