Question on GFP breaker for point of interconnection

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Anthonys

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We have a pv system design with 4 SMA TL-US 24000 Tripower inverters. It was our understanding, and that of our initial conversations with SMA that the backfeed breaker did not need to have GFP. However, plan review has called that it should be in accordance with NEC 705.32.

We are working through providing that for compliance; however, I was looking for some clarification on whether:

A. We actually do need this, SMA initially said that we did not need this with their inverters, now we have different information from a tech rep there. Anyone have any experience with this inverter and can speak to this?
B. Can we instead put the GFP on the combiner panel breakers, and have a much less expensive switchgear breaker that has GFP?

Thanks in advance for your input.
 
705.32 prohibits ground fault protection between the inverter and the utility, although it has an Exception. Is the reason you're being required to have GFP because there is GFP on the main service and you are connecting to the load-side of it, and this is being proposed as a means to meet the exception? If not then you should ask the plan checker to carefully re-read 705.32.

As far as question B, I would say that the answer is probably yes.

BTW, if there is GFP on the main service, good luck getting the manufacturer to say that you can backfeed that device. My understanding is that in many cases of larger services, the only solutions are a supply-side connection or a new service.
 
jaggedben said:
BTW, if there is GFP on the main service, good luck getting the manufacturer to say that you can backfeed that device. My understanding is that in many cases of larger services, the only solutions are a supply-side connection or a new service.
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That's news to me, and I have interconnected commercial PV through backfed breakers in large MDP's plenty of times.
 
ggunn said:
That's news to me, and I have interconnected commercial PV through backfed breakers in large MDP's plenty of times.
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I've never dealt with such a situation, so I defer to you. My comment was based on other comments made on this forum (e.g here), so let me ask you...

Have you never had an AHJ question if a main breaker with GFP was listed for backfeed?
 
jaggedben said:
I've never dealt with such a situation, so I defer to you. My comment was based on other comments made on this forum (e.g here), so let me ask you...

Have you never had an AHJ question if a main breaker with GFP was listed for backfeed?
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No, I don't believe any breakers I have installed have had it. The mains in the MDP frequently do, I believe.
 
ggunn said:
No, I don't believe any breakers I have installed have had it. The mains in the MDP frequently do, I believe.
Click to expand...

EDIT: Let me qualify that. I have never specified breakers with GFP in my designs, but we rely on our subcontractors to acquire and install them.
 
jaggedben said:
Is the reason you're being required to have GFP because there is GFP on the main service and you are connecting to the load-side of it, and this is being proposed as a means to meet the exception?
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Yes proposed a load side connection, and the MDP main has GF protection.

Apparently there are no three phase 480 breakers on the market that are listed for backfeed and ground fault protected. Should we invoke 90.4 in that case and ask for an exception? Or is the exception simply connecting to the line side?
 
shortcircuit2 said:
...A line side connection may be ahead of any existing metering to the building anyway.
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Which would be really bad for net metering!
BTW, my understanding of 705.32 is that they want to avoid the possibility that the PV will somehow source all of the unbalanced current into a ground fault in a connected load, preventing the GFP from tripping. Or maybe supply half of the 120ma of a fault current, preventing a 60ma GFP from tripping.
Which might perhaps, as noted, be prevented by putting separate GFP on the inverter connection. But there would still be the potential problem that 60ma on each of the two sources (main and GTI) would still allow 120ma to flow through the actual fault without detection.
With that interpretation, the only solution is to put GFP on all load circuits or on all feeders downstream of the PV connection point.
The Exception is very terse, and so somewhat ambiguous.
...provided that there is ground-fault protection for equipment from all ground-fault current sources.
Click to expand...
 
Anthonys said:
Apparently there are no three phase 480 breakers on the market that are listed for backfeed and ground fault protected. Should we invoke 90.4 in that case and ask for an exception? Or is the exception simply connecting to the line side?
Click to expand...

The code does not require that breakers be listed or identified, only that they be 'suitable'.

The 2011 code has an informational note to the effect that breakers not marked 'line' and 'load' are suitable. But this was removed in the 2014 code.

Another option may be to install a separate GFP device and, if it is directional, connect the 'line' to the inverter and the 'load' to the breaker.
 
Here is John Wiles statement on back-feeding GFP breakers from one of his 2014 proposed changes to 705.12(D) of the NEC...

"When a PV inverter feeds a load side connection, ground faults on load circuits that were previously protected by a main breaker ground fault protective device (GFP) and sourced by the utility may now be sourced by both the utility and the inverter. Stiff grids on large service entrances may hold line voltages up preventing the inverter?s anti-islanding systems from
shutting the inverter down when a ground fault occurs. Ground fault currents will be divided between the utility and the inverter and inverter supplied fault currents may prevent the main breaker GFP from activating at the desired set point. Engineering assessments are needed to determine circuit impedances for the division of fault currents between multiple sources and the appropriate settings for multiple ground fault protective devices. Manufacturers maintain most new main breaker GFP?s are OK for back-feeding, but cannot say about older units and for some the manufacturer may be out of business.The listing requirement has been deleted because accessories like GFP attachments to circuit breakers are not tested and listed for back-feeding. The manufacturer identifies which units are suitable for back-feeding."
 
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