Bonding Flexible Metal Conduit used for PV wire protection on the roof

T

tilden

Member
Location
Chapel Hill, NC, USA
We have a PV system with inverters that are adjacent to our array and are planning to use a short piece of flexible metal conduit to protect the PV conductors for the final few feet from when they leave the bottom of the array until they enter the inverter. Each end has a connector with plastic bushing inside for cable protection, and the end at the inverter will bond to the inverter via a lock-nut listed as capable of piercing paint to create a bond, so will qualify as bonded per NEC 2023 250.97 exception 3. This FMC will also contain a #6 bare ground wire to bond the inverter to the racking.

My question is whether we need to add a ground bushing to the distal end of the FMC underneath the array. This distal end of the FMC is not connected to any box or other metal component, so there is nothing that is being made continuous by bonding here.

We commonly use flexible nonmetallic conduit for this where no bonding is required at all, however this particular customer required all conduit to be metal.

Photo attached, and for anyone wondering - the fill and ampacity of those PV wires just barely works in that 1.5" FMC.
 

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So that's LFMC. Anyway...

It only needs to be bonded at one end. I'd probably do a grounding bushing at the inverter, as a best practice, but it's not code required if the inverter has a metal housing and the standard lockring is made up properly tight to remove any coating.
 
jaggedben said:
So that's LFMC. Anyway...

It only needs to be bonded at one end. I'd probably do a grounding bushing at the inverter, as a best practice, but it's not code required if the inverter has a metal housing and the standard lockring is made up properly tight to remove any coating.
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Yes, sorry I noted it as FMC instead of LFMC. I appreciate the reply that it only needs to be bonded at one end. Is there a specific code reference you may be able to help point me towards for that which I can utilize in case it's questioned at any point by an inspector or 3rd party firm?
 
tilden said:
Yes, sorry I noted it as FMC instead of LFMC. I appreciate the reply that it only needs to be bonded at one end. Is there a specific code reference you may be able to help point me towards for that which I can utilize in case it's questioned at any point by an inspector or 3rd party firm?
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Not exactly because that's kind of a proove-a-negative situation. Ask them to show you the code that requires it.

That said, it's important to understand that your 'ground' here is an equipment grounding conductor, not a grounding electrode conductor, and therefore 250.64(E) does not apply. Reading how 690.47 describes the EGC as permitted to be the only ground connection for the system could be helpful in that regard.
 
jaggedben said:
Not exactly because that's kind of a proove-a-negative situation. Ask them to show you the code that requires it.

That said, it's important to understand that your 'ground' here is an equipment grounding conductor, not a grounding electrode conductor, and therefore 250.64(E) does not apply.
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It's also worth noting that because 250.64(E) specifically requires bonding at both ends for some applications (a GEC), that means that bonding at both ends is not required in general. If it were, some section would say that, and 250.64(E) would not be present.

Cheers, Wayne
 
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