Table 250.66 Over 1100 cu./ Over 1750 Al.

[wireguy8169]

Ok,

Never really thought about it because I have never had to deal with it, but when sizing a grounding electrode conductor according to table 250.66 when you get to Over 1100kcmil cu. or over 1750kcmil Al. it seems by the way its written that 3/0 or 250kcmil is as large as you ever have to go, unlike the grounded conductor you would need to go to 12 1/2 % over 1100/1750kcmil.

Hope this make sense, but not sure if my thinking is correct, if not please refer me where to look.

Thanks

 

[chris kennedy]

it seems by the way its written that 3/0 or 250kcmil is as large as you ever have to go

Thats how I read it and install it. Other opinions may vary.

 

[DARUSA]

Grounding electrode conductor : to water main pipe# 3/0 maximum size required, ground rod #6,building steel #4 if I'm not wrong.

 

[DARUSA]

Main bonding jumper over 1100 kcmil 12-1/2 %.

 

[infinity]

Yes, #3/0 cu maximum size for GEC, over 1100 kcmil 12.5% for the bonding jumper. Same would apply to a transformer. Here's a photo of the #3/0 GEC and a 350kcmil bonding jumper:

 

[wireguy8169]

Thanks for all the replies

 

[DARUSA]

Yes, #3/0 cu maximum size for GEC, over 1100 kcmil 12.5% for the bonding jumper. Same would apply to a transformer. Here's a photo of the #3/0 GEC and a 350kcmil bonding jumper:

Infinity What is the reason to have 4 cables on the ungrunded wire ( and) 12 wires on the neutral ( grounded) wire? Harmonic?

 

[infinity]

Infinity What is the reason to have 4 cables on the ungrounded wire ( and) 12 wires on the neutral ( grounded) wire? Harmonic?

Actually it's a 500 kva with 5 sets of 500 kcmil ungrounded and 10 sets on the neutral (200%) for a Broadway theater with a large dimming load feeding a 1600 amp switchboard.