AC PVC disconnect tap from supply side

hhsting

Senior Member
I have service conductor on the line side of service disconnect tapped to an AC PV main disconnect. The question is should the neutral and ground bar of the Alternating Current (AC) PV main disconnect be bonded together i.e. main bonding jumper be in the AC PV main disconnect per NEC 2014 690 or possibly 705?????
 

jaggedben

Senior Member
Good question. There have been some knock down drag out arguments over this one in the past on this forum.

My advice. Decide if you want it to be a 'service disconnect', for any reason. If you do, bring the neutral there and put an MBJ. If you don't then run an EGC from the other service disconnect and leave neutral floating. Whichever you want, run it by your AHJ before installing. If it's a small system and/or you don't really have time for that, plan in such a way that you could do whichever the AHJ asks.

For what it's worth, in the 2020 NEC draft, the CMP seems to be moving away from the opinion that it's a service disconnect, without quite making that explicit. On the other hand, the definition of a service looks to be changing and that will take away one of the biggest arguments that it is not a service disconnect.
 

pv_n00b

Senior Member
Location
CA, USA
Go with what the AHJ wants. The NEC does not require one or the other, some AHJs will allow either and some only allow one. I expect there to be clarity in the 2020 NEC on the subject based on the drafts I have seen.
 

Carultch

Senior Member
Location
Massachusetts
This could come up in two different situations, where the AHJ / interpretation of the NEC might have a different answer in each.

1. A hot sequence meter for the building loads exists. You intend to connect between this hot sequence meter, and the corresponding main disconnect. Your PV system is still on the same service ("behind the meter"), but has a separate service disconnect. The main reason you might do this, is that system size makes it impractical to use the 120% rule and do a load side interconnection.

2. Your PV system will be a separate service from the service that feeds the building loads, but it will ultimately use the same utility-owned transformer and the same service conductors that drop from the transformer secondary. It connects on the line side of both the main service disconnect, and the meter for the main service that feeds building loads. It therefore has its own service disconnect, and its own utility service meter.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Go with what the AHJ wants. The NEC does not require one or the other, some AHJs will allow either and some only allow one. I expect there to be clarity in the 2020 NEC on the subject based on the drafts I have seen.
You are correct, sir. I went to a lecture at SPI on the 2017 and 2020 NEC given by a member of the group who are writing the code for 690 and related sections. She said that in 2020 the NEC will require N-G bonding at the disco for supply side PV interconnections.
 

hhsting

Senior Member
Good question. There have been some knock down drag out arguments over this one in the past on this forum.

My advice. Decide if you want it to be a 'service disconnect', for any reason. If you do, bring the neutral there and put an MBJ. If you don't then run an EGC from the other service disconnect and leave neutral floating. Whichever you want, run it by your AHJ before installing. If it's a small system and/or you don't really have time for that, plan in such a way that you could do whichever the AHJ asks.

For what it's worth, in the 2020 NEC draft, the CMP seems to be moving away from the opinion that it's a service disconnect, without quite making that explicit. On the other hand, the definition of a service looks to be changing and that will take away one of the biggest arguments that it is not a service disconnect.
The power flows from solar panels system to the AC PV main disco which outputs power to utility grid if the AC main disco is tapped from supply side of service disco feeding bldg. In normal secanrio without solar panel you have power flow from utility to service disco to the bldg.

How can one decide if AC PV disconnect is to be used as service disco?

Sent from my SM-G935U using Tapatalk
 

jaggedben

Senior Member
The power flows from solar panels system to the AC PV main disco which outputs power to utility grid if the AC main disco is tapped from supply side of service disco feeding bldg. In normal secanrio without solar panel you have power flow from utility to service disco to the bldg.

How can one decide if AC PV disconnect is to be used as service disco?
What I was trying to say was that there might be some reason, relating to the site details, that you prefer or don't prefer to bring a separate EGC to the solar disco. Whatever you prefer, run it by the AHJ before building.

The other advice given - ask the AHJ from the get go how they would like it done - is also good advice. Let them decide for you, especially if it makes no major difference to your bottom line.
 

hhsting

Senior Member
What I was trying to say was that there might be some reason, relating to the site details, that you prefer or don't prefer to bring a separate EGC to the solar disco. Whatever you prefer, run it by the AHJ before building.

The other advice given - ask the AHJ from the get go how they would like it done - is also good advice. Let them decide for you, especially if it makes no major difference to your bottom line.
AHJ says follow NEC 2014 . So if I do not place Main Bonding Jumper in the main PV AC disco and bring 3 phase conductors, 1 neutral to neutral bar from service conductor tap into PV AC main disconnect and bring 1 EGC from bldg main service disconnect ground bar into PV AC main disco ground bar that would also be ok?
 

jaggedben

Senior Member
AHJ says follow NEC 2014 . So if I do not place MBJ in the main PV AC disco and bring 3 phase, 1 neutral from service conductor tap and bring 1 EGC from bldg main service disconnect ground bar into PV AC main disco that would also be ok?
...
AHJ evidently has not considered the question before, or doesn't want to consider it, since 'follow the code' is a bit too vague on this point.

What you propose would be okay with some. Have you drawn it up and submitted plans?

I do believe that the disco must meet KAIC requirements and that it be suitable for use as service equipment even if you don't call it that. The utility might ask after that even if the AHJ doesn't.
 

hhsting

Senior Member
Current always goes back to the source so been told in fudamental electrical classes
So if there is a fault in PV solar system will it go to the place there is fault then to EGC to wherever MBJ is and then to what electric utility or back to solar panels? Its confusing and very confusing to place MBJ or not AC PV disconnect.
 

jaggedben

Senior Member
Current always goes back to the source so been told in fudamental electrical classes
So if there is a fault in PV solar system will it go to the place there is fault then to EGC to wherever MBJ is and then to what electric utility or back to solar panels? Its confusing and very confusing to place MBJ or not AC PV disconnect.
The available fault current from the utility will be tens of thousands of amps or higher, as it normally is.

The available fault current from the inverter(s) will be at most only marginally greater than its rated maximum operating output. It may be on the data sheet. In other words, most likely many times less than, if not totally insignificant compared to, the utility. You will most likely be relying on utility sourced current to open any OCPD in a sudden fault.

The MBJ may return fault current to both sources but it is typically only the grid that you have to worry about.

For this reason I've always thought that the PV disconnect should be treated like another service entrance. But some read the code legalistically, instead of with a mind to physics and safety, and determine that's not so.
 

hhsting

Senior Member
The available fault current from the utility will be tens of thousands of amps or higher, as it normally is.

The available fault current from the inverter(s) will be at most only marginally greater than its rated maximum operating output. It may be on the data sheet. In other words, most likely many times less than, if not totally insignificant compared to, the utility.

The MBJ may return fault current to both sources but it is typically only the grid that you have to worry about.

For this reason I've always thought that the PV disconnect should be treated like another service entrance. But some read the code legalistically, instead of with a mind to physics and safety, and determine that's not so.
What if bring neutral and phase service conductor tap into AC PV main disco, tie neutral to neutral bar and from neutral bar place GEC to electrodes possibly bldg electrodes and then to have MBJ from neutral bar to ground bar in the PV AC main disco. Your not brining any EGC to AC PV main disco. Would that be ok?
 

jaggedben

Senior Member
What if bring neutral and phase service conductor tap into AC PV main disco, tie neutral to neutral bar and from neutral bar place GEC to electrodes possibly bldg electrodes and then to have MBJ from neutral bar to ground bar in the PV AC main disco. Your not brining any EGC to AC PV main disco. Would that be ok?
Then you're treating it as a service disco. It's okay if the AHJ says so.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Then you're treating it as a service disco. It's okay if the AHJ says so.
FWIW, I went to a training session at SPI last week on the 2017 and proposed 2020 NEC. In all probability in 2020 this will be clarified to say that N-G bond happens in the disco. Until then it is subject to interpretation and either way is compliant.
 
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