NEC 2014 Grounding Question

infinity

Moderator
Staff member
Sounds like you're asking about how to calculate the SBJ when you have parallel secondary conductors. It's fairly straight forward you just add up the CM size of total number of ungrounded conductors per phase. So if you had 3 sets of parallel 250 kcmil your calculation would be 3*250 kcmil= 750 kcmil, this is your equivalent conductor size. You would then go to the table and find the SBJ size for a 750 kcmil conductor. They made it more complicated by using a conductor size (#3/0) that is not in circular mils.
 
I was trying to say that in the example they are saying that the SBJ is the one between X0 and the XFMR’s neutral bar, vs. the picture shows the SBJ as the one between the XFMR’s neutral bar and its enclosure.
 

infinity

Moderator
Staff member
Is this the section in question?

In this case, however, the system bonding jumper is installed at the transformer and connects the transformer neutral terminal (X0) to individual supply side bonding jumpers that are installed between the panelboard EC terminals and a terminal bus attached to the transformer enclosure.
 
Yes, my problem is with that statement. It says that the SBJ connects the X0 with SSBJ's, while on the picture the SBJ is that piece between the XFMR neutral bar and the XFMR enclosure.
 

infinity

Moderator
Staff member
I agree the wording in post #5 does not match the graphic that you've posted. The graphic does not have "a terminal bus attached to the transformer enclosure" it has a neutral bus and an SBJ connected to the enclosure.
 
Thank you! I understand now that there are many scenarios of system bonding jumper setups. The terminal bus attached to the XFMR enclosure (the scenario in the calculation example) serves as the connection point between the system bonding jumper and the grounding electrode conductor. This is a slightly different scenario than what Exhibit 250.14 shows, but it doesn't make either presentation wrong. Thanks again! Have a great day!
 
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