Bonding of EMT with non-metallic boxes and eccentric KOs

S

Solar_ice_caps

Member
Location
Florida
Occupation
Solar EPC
Just had a preliminary inspection for a solar install and a fail regarding lack of bonding for EMT.

Conduit path in question is as follows:

MSP >> Buried PVC >> Detached Garage Sub-panel (Metallic) >> EMT >> 60A Disconnect (Metallic) >> EMT >> PV Combiner (Non-Metallic) >> EMT/Flex >> PV Array JB (Non-metallic)

Circuit is 120/240 and has a green EGC through this entire path.

Inspector said I needed to bond both the (Garage Sub-panel (Metallic) >> EMT >> 60A Disconnect (Metallic)) AND (60A Disconnect (Metallic) >> EMT >> PV Combiner (Non-Metallic)) runs of EMT because they all us concentric KO's. Basically saying that the 60A disconnect (which is itself bonded to the EGC) is insufficient to path the connected emt through the concentric KOs.
My understanding is that because it's <250V and non-service, the connection at the garage subpanel alone would be sufficient even with concentric KOs.

Also said I need to bond the EMT between the non-metallic PV combiner and the non-metallic jbox on the roof. I think that one is valid. It's more previous only I'm unsure about.

Any insight would be great! We are on NEC 2017.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I presume the sub and disco are already bonded and the issue is putting a grounding bushing or some such on the EMT.

I think you are all around correct. That said, it's a common misunderstanding about extra bonding being required around eccentric and concentric KOs when the it's under 250V and not the service raceway. (It's not required.) So it might be smarter to just always do it to pass inspections. Plus I think extra bonding in exterior conditions on painted enclosures is just good practice.
 
S

Solar_ice_caps

Member
Location
Florida
Occupation
Solar EPC
Yes disco and sub are grounded.

Thanks, I agree with your approach as well, code notwithstanding. It’s a new-to-me inspector and not a battle I necessarily want to choose to fight right now.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Solar_ice_caps said:
My understanding is that because it's <250V and non-service, the connection at the garage subpanel alone would be sufficient even with concentric KOs.
Click to expand...
Yes systems that are less than 250 volt to ground do not require any additional bonding around concentric or eccentric KO's. The locknut on the EMT connector is all that's required.
 
S

shortcircuit2

Senior Member
Location
South of Bawstin
The EMT provides a path for fault current with or without a wire-type EGC inside that metal raceway.

The continuity stops at the EMT connection to the non-metallic combiner box. Installing the bonding bushing at that termination provides electrical continuity of the path for fault current to downstream equipment.
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Solar_ice_caps said:
green EGC through this entire path.
Click to expand...

Solar_ice_caps said:
Conduit path in question is as follows:

MSP >> Buried PVC >> Detached Garage Sub-panel (Metallic) >> EMT >> 60A Disconnect (Metallic) >> EMT >> PV Combiner (Non-Metallic) >> EMT/Flex >> PV Array JB (Non-metallic)
Click to expand...
I see:
MSP to Garage panel (Bonding jumper between enclosures "Buried PVC") Can be just the EGC bonded at each.
Garage panel to EMT (no additional bonding)
EMT to Disconnect to EMT (no additional bonding)
EMT to Combiner to EMT/Flex (NM box - bonding jumper between the EMT and the EMT/Flex)

"EMT/Flex"? You mean FMC or a coupling from EMT to Flex?
Depending on make up of the EMT/Flex (above question) Additional bonding at Array JB

All contingent on the concentric KO additional oversize rings not being compromised. Larger concentric KO's are harder to be used without compromising the non-removed rings from being damaged. (Even more so with NEMA 3 enclosures) Don't know what inspector saw.

Also he may be considering this section requirement but can't be sure as no pictures given, it would make additional bonding bushing or other means.
250.96(A)
Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or shall be connected by means of fittings designed so as to make such removal unnecessary.
 
S

Solar_ice_caps

Member
Location
Florida
Occupation
Solar EPC
Fred B said:
I see:
MSP to Garage panel (Bonding jumper between enclosures "Buried PVC") Can be just the EGC bonded at each.
Garage panel to EMT (no additional bonding)
EMT to Disconnect to EMT (no additional bonding)
EMT to Combiner to EMT/Flex (NM box - bonding jumper between the EMT and the EMT/Flex)

"EMT/Flex"? You mean FMC or a coupling from EMT to Flex?
Depending on make up of the EMT/Flex (above question) Additional bonding at Array JB

All contingent on the concentric KO additional oversize rings not being compromised. Larger concentric KO's are harder to be used without compromising the non-removed rings from being damaged. (Even more so with NEMA 3 enclosures) Don't know what inspector saw.

Also he may be considering this section requirement but can't be sure as no pictures given, it would make additional bonding bushing or other means.
250.96(A)
Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or shall be connected by means of fittings designed so as to make such removal unnecessary.
Click to expand...

"EMT/Flex"? You mean FMC or a coupling from EMT to Flex?

EMT transitioned to flex via a EMT/Flex coupler
(which actually then transitions back to EMT via an intermediary 4" metal box, but I didn't think that part was an issue since it's all securely bonded.)

I'm almost of the mind to put bushing at every termination from the sub-panel to the roof JB just to be safe, which would be 6 points. Those things are pricey though.

Here's a pic of the main issue (everything from MSP to subpanel was pre-existing):
down-net_http20231221-52-rsd99f.jpeg
The LB on the top left goes to the sub-panel KO, the non-metallic combiner on the right then continues on to the roof via the EMT and Flex mentioned. Don't mind the lack of raintight connectors...have another thread open for that :)
 
P

PCBelarge

Member
Location
Westchester County NY
Occupation
Electrical Training and Consulting
Over 250V to ground and/conductors other than service service conductors -
100 cu enclosure size is the 'magic' size. Under 100 cu in, the metallic enclosures/boxes have been tested for bonding and do not require additional bonding for metallic raceways/metallic sheath cables. Over 100 cu in, the enclosure has not been tested for bonding around concentric or eccentric KOs. If all KOs are removed or the entry is punched out, No additional bonding. If there are KOs in place with the metallic raceway/metallic sheathed cable installed, additional Bonding is required
 
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