705.12(D)(3) GFP and Supply Side Connections

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BillK-AZ

Senior Member
Location
Mesa Arizona
Something does not sound right about this.

Typically we have a main breaker | service entrance bus | inverter breaker | inverter.

Because your main breaker is required to have GFP, the 705.12(D)(3) Exception of this thread requires the inverter breaker to also have GFP.

You seem to have added an inverter GFP device so that you have:

Main breaker (with GFP) | service entrance bus | inverter breaker | GFP device | inverter

The main breaker and the inverter breaker are both required to be suitable for backfeed and also subject to possibly carrying ground fault currents.

A fault in the inverter could possibly cause the inverter to draw current from the grid and also cause ground fault currents.

The inverter breaker has two functions:
  1. It protects the main bus from excess inverter current (not likely in the real world), and
  2. It protects all of the wiring and devices on the load side of the inverter breaker in case there is a fault.

As I posted earlier, the manufacturer states that "GFP's can not be backfed in a PV/Solar application".

I do not understand how you can state " but the GFP is not backfed".
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
BillK,

I don't understand what issue you see with the installation, but I would certainly like to understand if there is a problem with it.

The exception to 705.12(D)(3) has 2 requirements. The first requirement is that there must be ground-fault protection for equipment from all ground-fault sources. In the event of a ground-fault anywhere in the premisis, the service disconnect will open protecting all equipment. At this point, the PV inverter is no longer a source of fault current because it shuts down as soon as it loses its connection to the grid. The first requirement is satisfied.

The second requirement is that ground-fault protection devices used with supplies connected to the load-side terminals shall be identified and listed as suitable for backfeeding. The inverter is the supply in this case, and it is connected to the line-side of the gfp. The second requirement is also satisfied.

It is important that the inverter have a maximum backfeed current rating of 0 amps to ensure that there will never be any current backfeeding the GFP device under normal circumstances. Under abnormal circumstances (fault in the inverter circuit), the circuit already has ground fault protection from the main, and over current protection from the inverter breaker.

I don't see any issue with the installation, and it appears to me to meet the NEC requirements of 705.12(D)(3).
 

BillK-AZ

Senior Member
Location
Mesa Arizona
Looks like that the manufacturer saying "DO NOT USE THIS IN A PV/SOLAR APPLICATION" is not good enough for you.

The device is marked 'line' and 'load' and you are installing it with the 'load' side to the utility. Good luck with the AHJ.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
I confirmed with the manufacturer today that the Multi 9 GFP can be appropriately installed in a PV system on the inverter output circuit in the manner I detailed above (inverter output connected to the line side of the GFP).
 

G._S._Ohm

Senior Member
Location
DC area
ground-fault current sources.

You may also want to research the difference between a "voltage source" and a "current source". An LED driver and fluorescent ballast are current sources, a wall outlet is a voltage source, and the driver and ballast convert one to the other.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
You may also want to research the difference between a "voltage source" and a "current source".... .

Hmm. I'm pretty sure that 'current source' is not being used in such a strictly technical fashion in this section of the code. It's being used to mean 'source of a ground fault current' and that includes the utility even though it would typically be considered a voltage source.
 

G._S._Ohm

Senior Member
Location
DC area
Hmm. I'm pretty sure that 'current source' is not being used in such a strictly technical fashion in this section of the code. It's being used to mean 'source of a ground fault current' and that includes the utility even though it would typically be considered a voltage source.
It is an unlikely choice for an answer but I wasn't sure the OP's question was finally answered. . .
 
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