Bonding feeder raceway

[smallfish]

I have a situation where 4 parallel sets of 4" emt conduits, each enclosing an equipment grounding conductor and their circuit conductors, stub up into an open-bottom 1600 amp 480/277volt panelboard. Each equipment grounding conductor is lugged to the panelboard frame and is bonded back at the source enclosure switchgear. The four conduits originating at the switchgear are bonded to it by means of set screw emt connectors each in their own punched hole. Do the stubbed-up ends of the conduits require bonding to the panelboard enclosure?

If these raceways are not bonded to the panelboard to which the equipment grounding conductors are, and a fault occured in a raceway, would the fault path be back to the source solely through the one faulted raceway? Would the fault current carried by the other paralleled circuit conductors of the same faulting phase (from the source to the panelboard and back, in the other direction, to the fault) be impeded? Would the equipment grounding conductors carry any of the fault current?

It would seem that 05NEC Sections 300.10, 250.96 and 250.97 would require raceway bonding to panelboard.

Thank You

 

[M. D.]

I have to run ,. so shooting from the the Hip ,.. they are bonded together at the source the equipmet grounding conductor is doing it's equipment grounding at the open bottom enclouser .. had the emt been used as the equipment ground?? a different story .

 

[acrwc10]

you need to look at 250.97. Just out of curiosity since you ran parallel conduits on a 1600 amp main, what size EGC did you run in each raceway ?

 

[smallfish]

EGC in each raceway is a 4/0 Cu.

 

[smallfish]

Does 250.97 require bonding of feeder raceway at both ends or just one end of conduit run?

 

[M. D.]

I found this,...http://expert.ecmweb.com/2008-National-Electrical-Code/
fourth question down ,.. there is relief for the mechanical connection and I think it would be hard to demonstrate that they are not electrically connected given the information provided

 

[tom baker]

What size are the circuit conductors? The EGC in each raceway must be full sized for the total KCMIL area of all the conductors

 

[Pierre C Belarge]

What size are the circuit conductors? The EGC in each raceway must be full sized for the total KCMIL area of all the conductors

4/0 is the proper size, see 250.122.

 

[don_resqcapt19]

I agree that 300.10 requires a bonding jumper at the open bottom panel.

 

[don_resqcapt19]

Also under the 2005 code there is no provison that permits the use of an open bottom enclosure. Yes it is a common practice, but the code did not permit it until 2008. 300.10 aludes to a permission for open bottom equipment, but it is not to be found in the 05 code.

 

[Pierre C Belarge]

Also under the 2005 code there is no provison that permits the use of an open bottom enclosure. Yes it is a common practice, but the code did not permit it until 2008. 300.10 aludes to a permission for open bottom equipment, but it is not to be found in the 05 code.

Don
If one wants to justify the use of open bottom equipment via the NEC, I believe one could reference 110.3(B).

 

[M. D.]

I agree that 300.10 requires a bonding jumper at the open bottom panel.

The open bottom enclosure is electrically connected to the EMT Is it somehow ineffective ???

 

[augie47]

I may be standing alone on this, but 300.16(B) seems that it could be used in this situation.

In any event, since it is Code compliant in 300.16 to terminate to an "open" switcboard by use of a bushing, I see no problem with the EMT's being dependant on the bond at the origin to provide the conduit ground.

We have a similar situation with a conduit "riser" to a weathehead. There is no requirement to bond at the weatherhead if the conduit is mechanically connected at the meter/disconnect.

In this situation, the EMTs are bonded on one end just as they would be on a riser or open switchboard. The requirement in 300.10 to "provide electrical continuity" is accomplished by the equipmemt grounding conductors.

 

[don_resqcapt19]

Don
If one wants to justify the use of open bottom equipment via the NEC, I believe one could reference 110.3(B).

Under the 2005 code, I don't see how 110.3(B) modifies the last part of 300.10.

300.10 Electrical Continuity of Metal Raceways and Enclosures
Metal raceways, cable armor, and other metal enclosures for conductors shall be metallically joined together into a continuous electric conductor and shall be connected to all boxes, fittings, and cabinets so as to provide effective electrical continuity. Unless specifically permitted elsewhere in this Code, raceways and cable assemblies shall be mechanically secured to boxes, fittings, cabinets, and other enclosures.

As far as I know there is no specific permission in the 2005 code.
That has changed with the 2008 code and the addition of Exception #2 to 300.12.

 

[don_resqcapt19]

The open bottom enclosure is electrically connected to the EMT Is it somehow ineffective ???

It is my understanding that there is not a bonding jumper between the EMT and the open bottom enclosure. I read the wording of 300.10 as requiring an electrical connection between the EMT and the enclosures at each and every enclosure.

 

[M. D.]

I guess I don't see why , in this instance the EGC doesn't not do it.

 

[don_resqcapt19]

I guess I don't see why , in this instance the EGC doesn't not do it.

It can do it, if it is bonded to the raceway at the open bottom enclosure. My reading of the section says that you must have an electrical connection between the raceway and the enclosure at each enclosure.

 

[M. D.]

Well , I will have to agree,. the more I read it the more I see it as a requirement for each enclosure .. I think the wording is weird though,.. the raceway has to be

" ......metallically joined together and shall be connected to all boxes so as to provide effective electrical continuity ...

does a 4\0 bonded to each emt accomplish this ? does the fact that the emt provides a far more superior conductor for a fault come into play?? would more current try to get through the bonding jumper than it can handle??

I'm only asking because what does effective electrical continuity mean in relation to that of the EMT.

Does any of this even make sense ???? I wish I new more,.. Gar are you out there ?:smile::-?:roll: