Parallel EGC

[electrofelon]

Think about Augie47's quote from Soares . . . the EGC has to be full sized because if there is a line to EGC fault in a run of parallel energized conductors the fault current into the EGC will come from both directions (from both ends) along the energized conductor. If you have only one of two conduits with a proper EGC, how do you know before hand that that is the conduit that will have the line to EGC fault?

But the fault can go "both ways" on the EGC too, so seems like, at least for two sets in parallel, a half size EGC in each pipe would be sufficient.

 

[al hildenbrand]

But the fault can go "both ways" on the EGC too, so seems like, at least for two sets in parallel, a half size EGC in each pipe would be sufficient.

I had a passing wonder at that, as well, . . . but I'll bet, in the presence of the plasma, the smaller the EGC, the quicker the plasma will cut it, likely not resulting in an effective fault current path of sufficient duration to operate the overcurrent protective device . . . maybe.

 

[Gary11734]

This thread has swerved way pass my pay rate!

 

[kwired]

If I was going to try this, I would at least not try and pull parallel runs under 1/0 since this is the minimum size to parallel for feeder conductors.

This problem is hypothetical. No one will do this or appears, has never tried.

Not hypothetical and is done at times.

If you are trying to parallel cable assemblies you can easily get into trouble. Usually a cable assembly EGC is sized per the ungrounded conductors in the cable and assumes they will be protected at their ampacity. If you paralleled two cables with 200 amp conductors and 6 or even 4 AWG EGC's - to get a 400 amp circuit your EGC's are too small for use with 400 amp OCPD.

Though not the topic of this thread cable assemblies also can get you into trouble with too small of an EGC at times for things like motor circuits where you are allowed to increase the OCPD over what you typically would for same size ungrounded conductors.

 

[Gary11734]

Not hypothetical and is done at times.

If you are trying to parallel cable assemblies you can easily get into trouble. Usually a cable assembly EGC is sized per the ungrounded conductors in the cable and assumes they will be protected at their ampacity. If you paralleled two cables with 200 amp conductors and 6 or even 4 AWG EGC's - to get a 400 amp circuit your EGC's are too small for use with 400 amp OCPD.

Though not the topic of this thread cable assemblies also can get you into trouble with too small of an EGC at times for things like motor circuits where you are allowed to increase the OCPD over what you typically would for same size ungrounded conductors.

Somewhere, I lost this thread from its original post.

 

[Wire-Smith]

Think about Augie47's quote from Soares . . . the EGC has to be full sized because if there is a line to EGC fault in a run of parallel energized conductors the fault current into the EGC will come from both directions (from both ends) along the energized conductor. If you have only one of two conduits with a proper EGC, how do you know before hand that that is the conduit that will have the line to EGC fault?

If you had a fault in a run of conductors and egc is insulated it would be either the metal conduit being the major circuit completing path at that location or if the fault melts the other conductors insulation in which case a circuit conductor to another circuit conductor is just as likely to be the major circuit completing path at that location. When paralleling, because of the common interpretation, you may be required a larger egc than the circuit conductors in the conduit. This is because this rule is of an arbitrary nature, because it's hard for AHJ's to calculate impedance and fault current. Although already covered at beginning of 250. the concern is fault current fusing/vaporizing small egc's(or a section of them(connections)).