Transformer Bonding Question

Status
Not open for further replies.
K

KWH

Senior Member
I am installing a Delta Wye xfmr and bonding @ the xfmr. There is a metal bonding strap ( from factory ) to the side of the case with a stud and is labeled ground, can I install all my grounds to the xo bar and the strap is the same as a bonding screw in a panel so there would be nothing attached to the ground stud.
 
KWH said:
I am installing a Delta Wye xfmr and bonding @ the xfmr. There is a metal bonding strap ( from factory ) to the side of the case with a stud and is labeled ground, can I install all my grounds to the xo bar and the strap is the same as a bonding screw in a panel so there would be nothing attached to the ground stud.
Click to expand...

Take a look at

250.30 Grounding Separately Derived Alternating-Current Systems. In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, and 250.26.
 
Most likely the strap you see is part of the transformer (think it may be a static shield) and has no real grounding to your XO.
(It is not the same as a panel bond strap).
You still need to bond XO to the can and install all your other required bonding/grounding.
 
The SBJ is my largest ground can you run this thru lug on XO than down to ground on frame and have all other grounds and low side neutral terminate on the XO buss.
 
augie47 said:
Most likely the strap you see is part of the transformer (think it may be a static shield) and has no real grounding to your XO.
(It is not the same as a panel bond strap).
You still need to bond XO to the can and install all your other required bonding/grounding.
Click to expand...

I agree in 25+ years I have never seen one that was factory bonded to the X0. Something similar to this:

75%20KVA%20Transformer%20Bonding%20Strap.jpg
 
Yes, it is the same type of strap and is mounted to the stud in the lower right, I took a quick look and lost sight of the other end of the strap heading towards the back of the xfmer and started thinking to much on the way home.
 
KWH said:
The SBJ is my largest ground can you run this thru lug on XO than down to ground on frame and have all other grounds and low side neutral terminate on the XO buss.
Click to expand...

Yes you can do it that way. There should be a few "ground" conductors that are all the same minimum size from T250.66. The GEC, the system bonding jumper, and the supply side bonding jumper to the secondary OCPD should all be the same unless you have a very large transformer where the system bonding jumper needs to be larger than #3/0 and calculated at 12.5% or parallel secondary raceways where the SSBJ's are sized according to the conductors within each parallel raceway.
 
Status
Not open for further replies.
Top