Equipment grounds in indoor 400kVA transformer

[Mccalabrese]

Hey guys, I'm new to posting, long time lurker. I'm an IBEW 01 JW, I was in the field for 7 years and just took a job with an electrical distributer as the gear quotes guy.

We have a contractor buying a 400kVA indoor transformer, and in my 7 years I've never installed that large of an indoor unit. He's got 4x 250KCMIL Equipment grounding conductors on the secondary side and 2x 1/0 EGC from the primary.

I'm not sure what to provide in terms of ground lugs or how to deal with that volume of EGC's in the enclosure, do any of you have experience with these, I'd like some kind of idea of the easiest way to deal with wire management for these grounding conductors..

Thanks!

 

[don_resqcapt19]

You don't have EGCs on the secondary of the transformer. You have supply side bonding jumpers and their sizing is from Table 250.102(C)(1), and based on the size of the ungrounded conductors.
Typically there is a bus bar provided for these connections, and if the system bonding jumper is installed at the transformer, you have to allow for the supply side bonding jumpers to connect to the system bonding jumper.

 

[Mccalabrese]

Right, I understand that, my question I suppose is that if I supply an 8 terminal lug is it going to be practical to try and deal with 4 250’s? It seems like a nightmare to manage and hit, I don’t know if it would be easier to bond multiple Lug sets to the enclosure, or if that’s even legal. Basically I’m curious what the easiest method of wire management will be for the contractor considering the volume of copper and the bending radius of these conductors

 

[Mccalabrese]

Basically they’re going to need the four SSBJs, the conductor to bond the secondarys neutral, the SBJ, and the two EGCs for the primary, and with the size of the conductors it feels like it’s going to be a major pain but I’m not sure how it’s usually dealt with

 

[infinity]

Why are the SSBJ's #250? Seems rather large for that secondary. The number of conductors you've proposed shouldn't be an issue.

 

[don_resqcapt19]

Why are the SSBJ's #250? Seems rather large for that secondary. The number of conductors you've proposed shouldn't be an issue.

I agree that four 250 kcmil supply side bonding jumpers sounds very large for a 400 kVA transformer.

 

[Mccalabrese]

Ah thank you for the picture! They have four parallels runs of 500KCMIL ungrounded conductors on the secondary so 2000 KCMIL total area aluminum

 

[infinity]

Ah thank you for the picture! They have four parallels runs of 500KCMIL ungrounded conductors on the secondary so 2000 KCMIL total area aluminum

Assuming that there are 4 raceways for secondary SSBJ's you can size each SSBJ based on the size of the secondary conductors in each raceway not the total of all the sets of secondary conductors.

 

[augie47]

Assuming that there are 4 raceways for secondary SSBJ's you can size each SSBJ based on the size of the secondary conductors in each raceway not the total of all the sets of secondary conductors.

(Thank you, I was trying to correctly word that and make sure I was reading 250.102(C) correctly )

 

[don_resqcapt19]

Ah thank you for the picture! They have four parallels runs of 500KCMIL ungrounded conductors on the secondary so 2000 KCMIL total area aluminum

Assuming four raceways, that would make the supply side bonding jumper 1/0 aluminum, in each, as you size that based on the size of the largest ungrounded conductor in each raceway and Table 250.102(C)(1). The system bonding jumper would be 250 kcmil aluminum, sized based on the total area of the four runs and that same table.

It looks like they may have been applying the full size EGC in each parallel raceway rule per 250.122(F)(1)(b), but you are not required to size the supply side bonding jumper that way.