250.122(g)

[chris kennedy]

I have a 150kva tranny, 208 Delta primary to 480y/277 secondary. From each ungrounded secondary bus I will have four #6's tapped to 4 AC disco's. The 208 primary is fed from a 400A breaker. Here is my confusion.

250.122(G) Feeder Taps.

Equipment grounding conductors run with feeder taps shall not be smaller than shown in Table 250.122 based on the rating of the overcurrent device ahead of the feeder but shall not be required to be larger than the tap conductors.

So essential there is no OCPD ahead of the taps, (SDS), so would I base the EGC on the 400A primary OCPD??? I understand it doesn't have to be larger than the tap conductors in this case, just wondering.

FWIW, this install will comply with 240.21(C)(4).

Thanks

 

[augie47]

I would think in this case that conductor would be considered an "system bonding jumper" and you would size it per 250.30.,the size being based on your #6s.

 

[chris kennedy]

Thanks Gus, hey, while I have your attention, how about fixing the thread title for me?:grin:

 

[chris kennedy]

I would think in this case that conductor would be considered an "system bonding jumper" and you would size it per 250.30.,the size being based on your #6s.

Wait a second, the system bonding jumper is in the tranny. So I now have EGC's leaving with the tap conductors.

 

[raider1]

Wait a second, the system bonding jumper is in the tranny. So I now have EGC's leaving with the tap conductors.

No, what you have are equipment bonding jumpers in accordance with 250.30(A)(2).

Chris

 

[augie47]

There has been a lot of discussion here previously as to proper identification of "that" conductor and one of the transformer install gurus may help me (Chris just did) . If we are to consider it an equipment grounding conductor, and it seems to fit that Art 100 definition, then the best I can do is fall back on 250.122(G) and say it does not have to be larger than the tap conductors.

 

[augie47]

The terminology game was played here:
http://forums.mikeholt.com/showthread.php?t=119166&highlight=equipment+bonding+jumper

It seems that is still considered an equipment bonding jumper.... as Chris (Jensen) says