Copper XFMR Secondary, Aluminum SBJ

[infinity]

I have a transformer with 4 set of 600 kcmil copper secondary conductors. The SBJ is aluminum how do you determine the proper size? Since we're over 1100 kcmil on the secondary conductors you would use the 12.5% rule for the SBJ but that would give you the copper SBJ size, how would that be converted to aluminum? I'm guessing but my choice would be to go to 250.122 and convert the copper SBJ size to the equivalent aluminum size. So I end up with this:

600*4=2400 kcmil * 12.5% =300 kcmil copper SBJ

T250.122 there is no 300 kcmil but for 350 kcmil you would use an equivalent SBJ of 600 kcmil aluminum. Looks good on paper.

 

[Joe Villani]

Rob,

SBJ System bonding jumper correct? (Just making sure)

Table 250.102(C)(1) note 2?


Convert the secondary conductor ampacity to equivalent aluminum and do the math?

Joe Villani

 

[infinity]

Yes, system bonding jumper @12.5%.

I guess that you could compare the ampacities of the two different metals and go from there.