Ground bushing connection

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I would like to know if a threaded rigid conduit (with GEC of separately derived system inside) installed to a pullbox in the following manner is physically secured:
Exterior of pullbox the conduit is secured with a lock nut.
Interior of pullbox the conduit is secured with an insulated grounding bushing only.
 
Re: Ground bushing connection

Don,
300.4(F) Insulated Fittings.
. . .Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. . .
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Is that it?

To me, a insulated grounding bushing is made mostly of metal with set screws and a lug and an insulating throat at the point that the conductors emerge. This type of bushing is mostly made of metal and is not covered by the above statement. The lug on the bushing is used for bonding the raceway to the GEC, so that covers 250.64(E), seems to me.

After I first read this question I went to the UL Certifications Directory to search and came up empty.

I've seen a lot of black RMC work with 100% metal bushings on the inside and a single hex nut on the outside of the j-box, and, after upwards of a century of service, the mechanical connection is still wrench tight. That seems to satisfy 300.10 (Electrical Continuity of Metal Raceways and Enclosures).

I haven't yet found a clear statement that this is not a correct assembly of fittings, raceway and enclosure.
 
Re: Ground bushing connection

Al, Yes, I was referring to an insulated metal ground bushing and that is exactly my question:
Is the locknut on the exterior and an insulated metal ground bushing with bonding cable on the interior proper assembly?
 
Re: Ground bushing connection

Al, Yes, I was referring to an insulated metal ground bushing and that is exactly my question:
Is the locknut on the exterior and an insulated metal ground bushing with bonding cable on the interior proper assembly?
Click to expand...
I would say no. At the least you would need to have bonding locknuts. Standard locknuts are not permitted when the raceway contains a GEC.
 
Re: Ground bushing connection

Sorry, I missed the part that said it was a grounding bushing. The installation is code compliant, as long as the bonding jumper connected to the grounding bushing is at least as large as the GEC. There is no requirement for locknuts on both sides of the enclosure.
Don
 
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