New to Engineering. Need help on this ASAP

[Timona]

Could you guys help me? I need an answer for the below.

I have a project. Client currently has a 2500kVA 13.8kV to 480V transformer and a 480V 3000A SWGR on site. Client want us to trench approximately 1750’ for the primary (direct burial) and connect the transformer from the existing substation. Then install (8) 3” PVC conduits each containing (4) 500MCM THHN and (1) 1/0 ground underground to the SWGR about 10’ away. With voltage drop we project to use a #3 minimum for the primary. Also, install a 4/0 bare CU ground ring around the transformer/SWGR pad w/ (4) ¾”x10’ ground rods, one at each corner. We would ground the transformer and gear with 4/0 tails from the ring. Y/N?

 

[infinity]

Then install (8) 3” PVC conduits each containing (4) 500MCM THHN and (1) 1/0 ground underground to the SWGR about 10’ away.

That seems fine. The 8 sets have an ampacity of 3040 amps. #1/0 is the correct size for the SSBJ in each raceway.

Also, install a 4/0 bare CU ground ring around the transformer/SWGR pad w/ (4) ¾”x10’ ground rods, one at each corner. We would ground the transformer and gear with 4/0 tails from the ring. Y/N

That is fine too, overkill but code complaint. Two 8' ground rods are all that's required.

 

[augie47]

Bob, If he meets the criteria from 250.30(A)(2) Exception, could the SSBJ not be omitted ??

 

[steve66]

That seems fine. The 8 sets have an ampacity of 3040 amps. #1/0 is the correct size for the SSBJ in each raceway.

That is fine too, overkill but code complaint. Two 8' ground rods are all that's required.

Doesn't it need to be a 500KCM ground in each conduit??
Sized per table 250.102(C)(1) for 8 sets of 500 KCM = 4000 KCM.
Footnote #1: The bonding jumper shall not have an area less than 12.5% of the area of the largest ungrounded supply conductor, or equivalent area for parallel supply conductors.
4000 * .125 = 500 KCM.

Bob, If he meets the criteria from 250.30(A)(2) Exception, could the SSBJ not be omitted ??

He mentioned PVC conduit, if you are asking if teh conduit can be used.

 

[augie47]

250.30 (A)(1) Exception allows a SBJ at the source and 1st disconnect under certain conditions (such as no parallel ground path) and 250.30(A)(2)
allows you to omit the SSBJ in that case. Seemingly applies here,.

 

[steve66]

NFPA's grounding fact sheet is just confusing me more on the Supply Side Bonding Jumpers. Page 5 gives two examples, one for Multiple SSBJ's, and one for a single SSBJ. How can we have a single SSBJ if there are multiple conduits?

Grounding & Bonding Fact Sheet Highlights Proper Application of Article 250 of the NEC | NFPA | NFPA

For those of us that employ NFPA 70, National Electrical Code (NEC) on a regular basis we understand the importance the NEC plays when it comes to the installation of safe electrical systems. In the early pages of the standard its purpose is clearly stated as the practical safeguarding of...

www.nfpa.org

 

[don_resqcapt19]

Doesn't it need to be a 500KCM ground in each conduit??
Sized per table 250.102(C)(1) for 8 sets of 500 KCM = 4000 KCM.
Footnote #1: The bonding jumper shall not have an area less than 12.5% of the area of the largest ungrounded supply conductor, or equivalent area for parallel supply conductors.
4000 * .125 = 500 KCM.


He mentioned PVC conduit, if you are asking if teh conduit can be used.

See 250.102(C)(2). Sized based on the ungrounded conductors in the individual raceways when there is a supply side bonding jumper in each raceway.