Bonding

[smallfish]

Four parallel sets of 4" emt stub up into the open-bottom of a 1600amp, 480/277v. panelboard and are not bonded to the enclosure. Equipment grounding conductors from the source enclosure, run in parallel with the feeder circuit conductors do terminate to the enclosure.
The panelboard is energized now and the EC asks if these feeder raceways can be bonded outside of the panelboard (in order to meet the requirements of 05NEC Sec.250.96 and 250.97 and 300.10.)
Fifteen feet upstream of the enclosure, bonding clamps would be secured to each emt. An equipment bonding jumper would be daisy-chained through each clamp and then immediately run into the raceway's 4' by 4' junction box. At this point, the jumper would be daisy-chained and split-bolted to each of the four equipment grounding conductors run in parallel with the circuit conductors.
Would this be an effective means of bonding and be code-compliant?
Thanks

 

[augie47]

are the conduits not bonded at the source either ?

If not, I see no problem with the "plan"

 

[smallfish]

Bonding

The four parallel conduits are bonded to the source enclosure (switchgear) by means of emt connectors through their own punched holes.

 

[augie47]

I may be overlooking something, but if the conduits are bonded at the source, metallic all the way and equipment grounds are pulled to bond your switchboard, I see no reason for the added "jumpers".

 

[SEO]

Gus what about 250.64 (E)?

 

[smallfish]

Bonding

If there is an insulation failure in one of phases in one of the conduits and because the conduit is only bonded to the source enclosure then it's very own connector will carry the entire fault current back to the source. Because the circuit conductors are run in parallel, the fault current will flow from both directions into the fault and still only the one conduit's connector, bonded only to the source enclosure, will bear the full extent of the fault current. Could the one set-screw emt connector clear the fault current? The 3 pole roll-out circuit breaker is set at 1200 amps. So is the need then to bond at both ends of the conduit?
Thanks

 

[augie47]

Gus what about 250.64 (E)?

In '08 that reference appears to be for grounding electrode conductor conduits

If there is an insulation failure in one of phases in one of the conduits and because the conduit is only bonded to the source enclosure then it's very own connector will carry the entire fault current back to the source. Because the circuit conductors are run in parallel, the fault current will flow from both directions into the fault and still only the one conduit's connector, bonded only to the source enclosure, will bear the full extent of the fault current. Could the one set-screw emt connector clear the fault current? The 3 pole roll-out circuit breaker is set at 1200 amps. So is the need then to bond at both ends of the conduit?
Thanks

I don't have the knowledge to answer that. I just don't see a Code section requiring it.