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Bonding Rules 250.97, 2002 NEC #103169
05/10/02 11:18 AM
05/10/02 11:18 AM
Joe Tedesco  Offline OP
Member
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
QUESTION FROM: John J. Deery ,

Joe my question is about 250.97. If you run a branch circuit to a safety switch and the conduit enters the enclosure through concentrics or eccentrics, are you required to use bonding bushings when the voltage excedes 250 volts to ground and you pull an equipment grounding conductor and bond it to the enclosure?

My concern: "Is the conduit being properly bonded?"

I spoke to Kevin Huss from Square D at 800-634-2003 TEC support, and was told to date Square D does not have an enclosure on the market with pre-stamped ko's listed by U.L. for the purpose of bonding.

We have new branch circuits being run at our plant 480 volts where the conduits are being landed in pre-stamped ko's of Square D enclosures with equipment grounding conductors, but are relying on the eccentrics and concentrics to bond the conduits.

Thanks


Joe Tedesco, NEC Consultant
2017 / 2014 NEC & Related Books and Study Guides
Re: Bonding Rules 250.97, 2002 NEC #103170
05/10/02 02:12 PM
05/10/02 02:12 PM
R
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
The conduit needs to be effectively bonded to the installed EGC through a bonding bushing because if a fault developed in the raceway, the return path may not have a low enough impedance to assure opening of the OCPD.
Don,
are you wondering if the conduit is effectively bonded at the supply end, and therefore not required to be bonded through a bushing at the switch end?

Re: Bonding Rules 250.97, 2002 NEC #103171
05/11/02 07:17 PM
05/11/02 07:17 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Some suggestions...Square-D makes NEMA-12 [NOT '12K' or ‘AWK’ suffix] XOP fusible disconnect switches without knockouts. Westinghouse/C-H makes NEMA-12 breaker enclosures of similar construction. Many 5½" depth panelboard cans are available with 'blank endwalls.' The 12’s are equal or somewhat less in price compared to 3R. ‘NOKO’ NEMA-1, -3 and -3R screw-cover gutters and pull cans are out there too.

KO reducing rings are {or should be} suicide.

Re: Bonding Rules 250.97, 2002 NEC #103172
05/11/02 10:13 PM
05/11/02 10:13 PM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Redsy,
That is exactly what I was thiniking. Most code experts say that only one end of a service raceway requires bonding, so I would think that if the supply end was properly bonded, there would be no need to bond the load end, assuming that the EGC is used to bond the enclosure.
Don(resqcapt19)


Don(resqcapt19)

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