gtout
Member
- Location
- Princeton NJ
Greetings all, this is my first post. I'm a design engineer from Princeton NJ with about 30 years experience.
I have an installation of a 750kW PV system. The collector switchgear at the array side is about 1300' away from the utility tie-in point. Since the feeder is rated 1200A at 480VAC we have a GF relay on the main (Siemens HNG3B120L and external GF relay iGard MGFB-1200-ZB). The output is a series of (99) single-phase distributed inverters connected "wye." Note we did not bond the neutral to ground here.
At the tie-in point to the utility we installed a 2nd 1200A breaker (Siemens NNG3B120L with internal trip unit 576) ahead of the tap to the switchgear bus. The tap conductors are downstream of the main 1600A breaker and upstream of the utility C/Ts as required by the utility. We terminated the neutral conductors ahead of the GF sensors on the main and the neutral bonding jumper is right there. So as far as we can tell, there are not multiple paths to ground where GF current might leak around a sensor.
The problem arose when the local AHJ insisted that the 2nd 1200A breaker also be equipped with GF protection. We are getting what we believe to be nuisance GF trips on this 2nd breaker, 3 times in approx 3 months. We had a setting study performed but we're still getting trips. The installer has meggered all cables after each event but the cables are fine. In desperation, we set the relay to its least sensitive setting but we're still tripping out for no apparent reason.
We thought we didn't need the 2nd GF relay and referred the local AHJ to NEC Article 215 in a letter:
"We believe that we are in compliance with NEC Article 215.10 Exception No. 2 in that we have provided GF protection at the PV switchgear at the solar array which is the supply side of this feeder (there are no transformers). This protects the entire feeder right up to the point of connection to the main switchgear including the disconnect in question. The key is that we?re not bonding the neutral at the PV gear. Any potential ground fault current can only find its way back to the utility transformer X0 point via the single bonding jumper in the main gear. We are unaware of any NEC article that requires more than one GF protection means on a single feeder."
The local AHJ did not agree and required the 2nd GF relay. Any insight or opinions on whether this 2nd GF relay is required or what our problem might be?
Thanks,
Garry Out
I have an installation of a 750kW PV system. The collector switchgear at the array side is about 1300' away from the utility tie-in point. Since the feeder is rated 1200A at 480VAC we have a GF relay on the main (Siemens HNG3B120L and external GF relay iGard MGFB-1200-ZB). The output is a series of (99) single-phase distributed inverters connected "wye." Note we did not bond the neutral to ground here.
At the tie-in point to the utility we installed a 2nd 1200A breaker (Siemens NNG3B120L with internal trip unit 576) ahead of the tap to the switchgear bus. The tap conductors are downstream of the main 1600A breaker and upstream of the utility C/Ts as required by the utility. We terminated the neutral conductors ahead of the GF sensors on the main and the neutral bonding jumper is right there. So as far as we can tell, there are not multiple paths to ground where GF current might leak around a sensor.
The problem arose when the local AHJ insisted that the 2nd 1200A breaker also be equipped with GF protection. We are getting what we believe to be nuisance GF trips on this 2nd breaker, 3 times in approx 3 months. We had a setting study performed but we're still getting trips. The installer has meggered all cables after each event but the cables are fine. In desperation, we set the relay to its least sensitive setting but we're still tripping out for no apparent reason.
We thought we didn't need the 2nd GF relay and referred the local AHJ to NEC Article 215 in a letter:
"We believe that we are in compliance with NEC Article 215.10 Exception No. 2 in that we have provided GF protection at the PV switchgear at the solar array which is the supply side of this feeder (there are no transformers). This protects the entire feeder right up to the point of connection to the main switchgear including the disconnect in question. The key is that we?re not bonding the neutral at the PV gear. Any potential ground fault current can only find its way back to the utility transformer X0 point via the single bonding jumper in the main gear. We are unaware of any NEC article that requires more than one GF protection means on a single feeder."
The local AHJ did not agree and required the 2nd GF relay. Any insight or opinions on whether this 2nd GF relay is required or what our problem might be?
Thanks,
Garry Out