Parallel Supply Side Bonding Jumper vs Equipment Grounding Conductor

[32Laterlaus]

First off, to clear up the SSBJ. Lets say I have a transformer. I come off that transformer with 3 hots, a neutral, a 'ground' to a panel, and then a Grounding Electrode Conductor (GEC) on the side. Since this is a separately derived system before an OCPD, that 'ground' would be a SSBJ, correct?

Now the 'ground' past that first OCPD would be an Equipment Grounding Conductor (EGC), correct?

1. So my main question is in regards to parallel sets. Let's say ive got an 800A feed from Dist to Panel (EGC):
3 sets of the following:
4 #350K
1 #1/0 GND ...250.122 (EGC)
3"C
So we essentially use 3 sets of the #1/0 EGC because 250.122(F)(1)(b) says we need the EGC in every raceway fully sized per 250.122 and cites ground fault as the reason for having it fully sized for each parallel since the fault may be felt unevenly by one of the parallel runs.



2. Now onto the SSBJ, lets say same 800A feed, but now from XFMR to Panel:
3 sets of the following:
4 #350K
1 #2 GND ...250.102(C)(1) (SSBJ)
3"C
#2/0 GEC on the side
The #2/0 GEC I see as being 'fully sized' based on the equivalent area of the parallel conductors, but the SSBJ gets to have just #2 in each based on the #350k. This seems to conflict with 250.122(F)(1)(b) for the EGC. Why does the ground fault reasoning for fully sized EGC not apply here?

Why is the SSBJ allowed to be essentially less compared to the EGC? Anything Im misunderstanding?

Thank you

 

[infinity]

The #2/0 GEC I see as being 'fully sized' based on the equivalent area of the parallel conductors, but the SSBJ gets to have just #2 in each based on the #350k. This seems to conflict with 250.122(F)(1)(b) for the EGC. Why does the ground fault reasoning for fully sized EGC not apply here?

Why is the SSBJ allowed to be essentially less compared to the EGC? Anything Im misunderstanding?

Thank you

In this case the parallel SSBJ's (3 of them) are large enough. If you have one raceway, say a wireway, you would have a #2/0 SSBJ. Your combined #2's should be roughly the equivalent or larger than the #2/0.

 

[32Laterlaus]

In this case the parallel SSBJ's (3 of them) are large enough. If you have one raceway, say a wireway, you would have a #2/0 SSBJ. Your combined #2's should be roughly the equivalent or larger than the #2/0.

Right, so the (3) #2 essentially add up to the 2/0. I guess my question then is for the EGC, why cant I divide the equivalent area of the #1/0 into (3) smaller conductors, why must they all be #1/0?

Edit: I know its because the code says so, but is there any reasoning behind the difference?

 

[infinity]

Right, so the (3) #2 essentially add up to the 2/0. I guess my question then is for the EGC, why cant I divide the equivalent area of the #1/0 into (3) smaller conductors, why must they all be #1/0?

Edit: I know its because the code says so, but is there any reasoning behind the difference?

With an EGC they want any one of the parallel EGC's to be able to carry all of the fault current. Maybe someone else will chime in with the actual reason that it's needed to be that way.

 

[32Laterlaus]

With an EGC they want any one of the parallel EGC's to be able to carry all of the fault current. Maybe someone else will chime in with the actual reason that it's needed to be that way.

Yeah I was under the same understanding, wasn't sure why the SSBJ isn't treated that way as well??

 

[don_resqcapt19]

...
Why is the SSBJ allowed to be essentially less compared to the EGC? Anything Im misunderstanding?
...

Thank you

This is just a code rule with zero technical substantiation. The worst case as far as fault clearing is with the SSBJ, yet it is permitted to be made up of less copper than the EGC. It almost got fixed in the 2020 code, maybe they will fix it for the 2023.

 

[32Laterlaus]

This is just a code rule with zero technical substantiation. The worst case as far as fault clearing is with the SSBJ, yet it is permitted to be made up of less copper than the EGC. It almost got fixed in the 2020 code, maybe they will fix it for the 2023.

Good to know! Well I guess as long as the feeders I posted are all code compliant, im happy for now.