# Thread: System Bonding Jumper Size calculation?

1. Member
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## System Bonding Jumper Size calculation?

Sorry I have one more question, this one I am pretty lost on. Even though it is probably pretty simple. It seams like the more I try and study the more confused I get haha..

Scenario 305-45
A 500 KVA, 480 delta to 208/120-volt, 3-ph, 4-W transformer is to be installed.
• One set of secondary conductors is installed from the transformer to a 600-A Main Breaker (MB) panelboard.
• There will be three parallel conduits to this 600-A panel. Each conduit will contain 4 each 3/0 conductors.
• A second set of secondary conductors is installed from the transformer to a 300-A MB panelboard. One conduit will be installed between this 300-amp panel and the transformer. The conduit will contain 4 each 350 kcmil conductors.
• You have decided to satisfy the “grounding and bonding” requirements inside each panelboard.

Refer to Scenario 305-45 to answer this question. The smallest SBJ you can install in the 600-A PB is ___ AWG.

So... We know that there are 3 paralleled feeders to a 600 amp main breaker. Each conduit contains 3/0 conductors. I'm looking for the System Bonding Jumper wire size. I am completely lost. I do know though that I am going to have to use table 250.102(C)(1). I just don't understand how to add up all the 3/0 conductors and how to come out with a SBJ size

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Originally Posted by JasonCo
Sorry I have one more question, this one I am pretty lost on. Even though it is probably pretty simple. It seams like the more I try and study the more confused I get haha..

Scenario 305-45
A 500 KVA, 480 delta to 208/120-volt, 3-ph, 4-W transformer is to be installed.
• One set of secondary conductors is installed from the transformer to a 600-A Main Breaker (MB) panelboard.
• There will be three parallel conduits to this 600-A panel. Each conduit will contain 4 each 3/0 conductors.
• A second set of secondary conductors is installed from the transformer to a 300-A MB panelboard. One conduit will be installed between this 300-amp panel and the transformer. The conduit will contain 4 each 350 kcmil conductors.
• You have decided to satisfy the “grounding and bonding” requirements inside each panelboard.

Refer to Scenario 305-45 to answer this question. The smallest SBJ you can install in the 600-A PB is ___ AWG.

So... We know that there are 3 paralleled feeders to a 600 amp main breaker. Each conduit contains 3/0 conductors. I'm looking for the System Bonding Jumper wire size. I am completely lost. I do know though that I am going to have to use table 250.102(C)(1). I just don't understand how to add up all the 3/0 conductors and how to come out with a SBJ size
Based on your comments, I don't think you are completely lost. You just need to convert the 3/0 to circular mils and go from there. Hint, find the conductor properties to convert in Chapter 9.

3. Member
Join Date
Mar 2016
Location
Houston, Texas
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Originally Posted by texie
Based on your comments, I don't think you are completely lost. You just need to convert the 3/0 to circular mils and go from there. Hint, find the conductor properties to convert in Chapter 9.
AWesome Thanks! So lets try this.

Chp 9 Table 8. Circular Mils will be 167800
167800 x 3 = 503400

Now I take that number and go back to 250.102 table? So 503.4 is 1/0 wire size?

4. Originally Posted by JasonCo
AWesome Thanks! So lets try this.

Chp 9 Table 8. Circular Mils will be 167800
167800 x 3 = 503400

Now I take that number and go back to 250.102 table? So 503.4 is 1/0 wire size?
Correct for a copper SBJ.

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