FMT Bonding on transfer switch

Status
Not open for further replies.
J

john8791

Member
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.
 
Reducing washers are listed for grounding and bonding where all the concentric or eccentric rings are removed.

Chris
 
raider1 said:
Reducing washers are listed for grounding and bonding where all the concentric or eccentric rings are removed.

Chris
Click to expand...

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.
 
john8791 said:
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.
Click to expand...

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
 
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.
Click to expand...
 
So, we should expect that the box's factory-installed connector is adequately bonding the FMC.
 
Interestingly enough, inside the transfer switch, the paint is not scraped. just fitting with one locknut inside.
 
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
 
izak said:
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
Click to expand...

Oops. I meant to write FMC. Must have combined FMC and EMT. Just a brain fart.
 
izak said:
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
Click to expand...
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:
john8791 said:
It is only 18" and not being used as an EGC. The EGC is running through it. The concern was proper bonding.
Click to expand...
As long as at least one of its connectors is bonded through its attachment to a bonded enclosure, it's bonded.
 
Status
Not open for further replies.
Top