FMT Bonding on transfer switch

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john8791

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Location
Iowa, US
Occupation
Electrical Engineer
A Reliance brand load-side transfer switch is installed with 18" of FMT (preinstalled with wires run through including an EGC) connected to main panel. The installation would seem to comply with NEC 250.118(5) as the circuits are 20A or less thereby not requiring separate bonding. However, the fitting to the main panel was installed into a 1" knockout that was reduced to 3/4" with reducing washers. Does that change the requirement? Thanks.
 

raider1

Senior Member
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Location
Logan, Utah
Reducing washers are listed for grounding and bonding where all the concentric or eccentric rings are removed.

Chris
 

john8791

Member
Location
Iowa, US
Occupation
Electrical Engineer
Reducing washers are listed for grounding and bonding where all the concentric or eccentric rings are removed.

Chris

That surprises me. Aren't you basically relying on the washer to make good contact with the bare metal within the cut out? I may use a bonding bushing anyway.
 

raider1

Senior Member
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Location
Logan, Utah
That surprises me. Aren't you basically relying on the washer to make good contact with the bare metal within the cut out? I may use a bonding bushing anyway.

I was suprised as well the first time I heard that reducing washers were listed for grounding.

If you have the UL White book the information can be found in Product catagory (QCRV) under Outlet bushings and fittings.

Chris
 

iwire

Moderator
Staff member
Location
Massachusetts
I was also surprised, it seems if you were to use reducing washers as the grounding means strict adherence to 250.12 would be required.

250.12 Clean Surfaces. Nonconductive coatings (such as
paint, lacquer, and enamel) on equipment to be grounded
shall be removed from threads and other contact surfaces
to ensure good electrical continuity or be connected by
means of fittings designed so as to make such removal
unnecessary.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
So, we should expect that the box's factory-installed connector is adequately bonding the FMC.
 

john8791

Member
Location
Iowa, US
Occupation
Electrical Engineer
Interestingly enough, inside the transfer switch, the paint is not scraped. just fitting with one locknut inside.
 

izak

Senior Member
Location
Springfield, MO
can someone describe to me what FMT is? I noticed that the OP used that term, and I saw that it was FMC, and i know that some people confuse the two in the code, saying that 'flex' cannot be used in lengths over six ft.

but ive never been able to find a picture of it
 

john8791

Member
Location
Iowa, US
Occupation
Electrical Engineer
can someone describe to me what FMT is? I noticed that the OP used that term, and I saw that it was FMC, and i know that some people confuse the two in the code, saying that 'flex' cannot be used in lengths over six ft.

but ive never been able to find a picture of it

Oops. I meant to write FMC. Must have combined FMC and EMT. Just a brain fart.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
can someone describe to me what FMT is? I noticed that the OP used that term, and I saw that it was FMC, and i know that some people confuse the two in the code, saying that 'flex' cannot be used in lengths over six ft.

but ive never been able to find a picture of it
Flexible Metallic Conduit, aka Greenfield. Like MC, but empty. You need to use bushings at every connector (unless their design includes it).

Flex cannot be used as an EGC in lengths over 6' and over 20a. Otherwise, add an EGC.

Added:

2009430163817.jpg
 
Last edited:

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
It is only 18" and not being used as an EGC. The EGC is running through it. The concern was proper bonding.
As long as at least one of its connectors is bonded through its attachment to a bonded enclosure, it's bonded.
 
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