250.122 (F) (2) - I don't get it

[jes25]

This section of the code as shown in the graphic doesn't "feel" right to me. How is it I can have a single EGC entering a cabinet all itself with parallel cables? I can't get over entering an EGC though a metal enclosure without grouping. Could someone explain why this is OK?

What if the parallel cables pass though pipe nipples with the single EGC not grouped. Does that change anything?

 

[infinity]

It appears that the single conductor is just bonding the cable tray since it is not mechanically connected to the enclosure.

 

[jes25]

It appears that the single conductor is just bonding the cable tray since it is not mechanically connected to the enclosure.

No, that's the EGC as permitted in 250.122 (F) (2)

 

[don_resqcapt19]

Unless you special order the cables with an oversized EGC, there is no other way to install paralleled cables as the code requires that the EGC in each cable be sized to the OCPD that protects the paralleled sets. The rule for tray acts as an exception to that and permits the single external EGC in the tray, but it does not address how you would make the entries into the equipment.

 

[LarryFine]

How is it I can have a single EGC entering a cabinet all itself with parallel cables?

Because it's not a current-carrying conductor (normally).

 

[jes25]

Thanks for the responses. I have an install where we installed parallel TC cables as shown in the graphic, but passed them through individual pipe nipples. The single EGC is ran with one of the parallel sets and I started thinking I have a grouping problem. The nipples in question are through a wall not into the equipment.

 

[ramsy]

passed them through individual pipe nipples.

If concerned with 110.36 fault damage from magnetic forces, and 300.20(B) fault impedance passing thru ferrous nipples, both may be reduced by bonding bare EGC to each nipple, perhaps by using split bonding bushings.

 

[jes25]

If concerned with 110.36 fault damage from magnetic forces, and 300.20(B) fault impedance passing thru ferrous nipples, both may be reduced by bonding bare EGC to each nipple, perhaps by using split bonding bushings.

Yea, that is what was bugging me thanks.

In a similar vein, is it permitted to pass a bonding jumper through a ferrous loop or nipple? 250.102 seems to allow it. Is it a good idea?

 

[ramsy]

250.102 seems to allow it. Is it a good idea?

Yes I see that also, both 250.102(E), and 250.130(C) appear to allow bare copper on exteriors of enclosures & raceways, and allow single EGC's to be routed thru ferrous boxes.

Those ferrous exteriors are also intended to be bonded at the same potential as the routed copper, per 250.86, etc..

 

[ramsy]

is it permitted to pass a bonding jumper through a ferrous loop or nipple?

It appears 250.132, and 300.10 wants that nipple bonded.

Perhaps a threaded split bushing is not needed, if the ferrous parts are bonded elsewhere.

 

[jes25]

It appears 250.132, and 300.10 wants that nipple bonded.

I'm not so sure about that.....

300.10 Exception 1 permits a short section, aka nipple.

250.132 says "IF required to be connected to an EGC" (emphasis on IF)...which I say it's not an IF per 250.86 Exception 2.

 

[ramsy]

Roger that, exceptions will apply, but raceways wont be deliberately designed with inductive chokes, avoided per 300.20(B).

A better design would use non-ferrous nipples, aluminum or rigid PVC.