bonding for parallel ungrounded conductors

[jmfelectric]

greetings forum,


2014 NEC art 250.102 (c) (2) states the following: where the ungrounded supply conductors are paralleled in two or more raceways or cables, and an individual supply-side bonding jumper is used for bonding these cables or raceways, the size of the supply side bonding jumper for EACH cable or raceway shall be based on and selected from table 250.102 (c) (1)

A single supply side bonding jumper installed for bonding two or more raceways or cables shall be sized in accordance with table 250.102 (c) (1)

in English, does the second part of the requirement mean that I can use one bonding jumper for all the cables as long as it is sized for the sum of the paralleled ungrounded conductors?

 

[infinity]

This is for a transformer installation?

 

[jmfelectric]

I think I am confusing a few terms this morning (rough Saturday night) .

Basically, I have a 690 volt/595 amp/660 kw wind turbine generator. The manufacturer (vestas) provided 4, 3 conductor (#2 copper )cables (+ground) that go between the generator and the down tower main breaker.

even before adding 115% to the generator, we know these cables are too small. At this point, my calculation is 683 amps divided among the 4 paralleled conductors bringing me to 170 amps per or 4, 2/0 conductors paralleled.

The manufacture's rep wants to replace the cables with 3, conductor cables and run external grounds. I'm trying to figure out the size of the ground and I think I am confusing bonding jumpers, grounding electrode conductors and equipment grounding conductors.

which would apply in this scenario?

 

[don_resqcapt19]

I think I am confusing a few terms this morning (rough Saturday night) .

Basically, I have a 690 volt/595 amp/660 kw wind turbine generator. The manufacturer (vestas) provided 4, 3 conductor (#2 copper )cables (+ground) that go between the generator and the down tower main breaker.

even before adding 115% to the generator, we know these cables are too small. At this point, my calculation is 683 amps divided among the 4 paralleled conductors bringing me to 170 amps per or 4, 2/0 conductors paralleled.

The manufacture's rep wants to replace the cables with 3, conductor cables and run external grounds. I'm trying to figure out the size of the ground and I think I am confusing bonding jumpers, grounding electrode conductors and equipment grounding conductors.

which would apply in this scenario?

That would be a violation of 300.3(B).

 

[rlundsrud]

The ground is actually a PE or EGC. THE breaker in this turbine is a 630 amp breaker (labeled Q8) so you would only need cable ampacity equal to that. You don't need to use a 115% correction factor as far as I can see. I could not find what the termination temperature rating was, but I believe it to be 75°C. This unit has a wye configuration with no neutral, so you would bond the center of the wye to your EGC. I don't know if the unit has a transformer with it prior to connection to the utility, but I would guess it would be a delta output. If there is a transformer it would be corner grounded to your PE/EGC.

 

[jmfelectric]

thanks Don, for the 300.3 violation. I thought it was there, but couldn't find it.

Rlunsrud, wouldn't 445.13 ampacity of conductors, require me to add 115% to the nameplate of the generator in sizing the conductors?

As always, thanks for everyone's comments!

 

[jmfelectric]

Hey Don,

would 250.102 (E) allow the ECG to be run outside the cable assembly?

John

 

[don_resqcapt19]

Hey Don,

would 250.102 (E) allow the ECG to be run outside the cable assembly?

John

John,
Nothing in 250.102 applies to EGCs. However, I don't think you have EGCs in your application. I think that they are supply side bonding jumpers.
The section you cited may permit the external jumper, but I don't have enough of an understanding of your installation to be sure.