Transformer xo

[hawkeye23]

Can someone answer this.,When connecting xo to the case of transformer should the bond be the same size conductor as the ?
Thanks

 

[infinity]

Do you have a guess? The question is poorly written bevcuase there are times where the SBJ is larger than the "other" conductor.

 

[hawkeye23]

Its a 4 wire 460 to 208/120 . It is 3phase 45 kvA transformer. I am not sure if the bond from xo should the same size as the neutral conductor. Will bond and ground in trans.
I hope this helps. Thanks for your help.

 

[infinity]

You're asking about the system bonding jumper (SBJ). You would size this according to T250.66 based on the size of the derived secondary conductors and would be the same size as the GEC but T250.66 stops at #3/0 Cu so if your secondary conductors were larger than the largest conductor listed in T250.66 then you would need to size the SBJ at 12.5% of the derived conductors.

 

[iceworm]

Its a 4 wire 460 to 208/120 . It is 3phase 45 kvA transformer. I am not sure if the bond from xo should the same size as the neutral conductor. Will bond and ground in trans.
I hope this helps. Thanks for your help.

As infinity has said, the guide is T250.66 (not limited to 3/0). The neutral conductor size is not particularly relavent.

Additional references:
250.28.D.3 which takes you to
250.28.D.1 which takes you to
T250.66
Alos look at T250.66, note 2 and note a

My current practice is to size the SBJ, GEC using the xfm secondary conductor size (normally based on fla x 1.25), and T250.66. Unless for some odd reason the conductors are small, then I tend to use note 2 and size SBJ for the maximum size conductors that could be required.

ice

 

[infinity]

As a rule of thumb for smaller transformers, like the 45kva mentioned in post #3, usually the SBJ, GEC and SSBJ will all be the same size. Once you get into parallel secondary conductors and secondaries above 1100 kcmil cu things change.