Supply side bonding jumper

Status
Not open for further replies.
S

Shane30

Member
Location
Tennessee
Occupation
Electrician
Here’s the scenario. Brand new 4000A switch gear, brand new utility transformer. 11 parallel feeder conduits between the two. Each conduit has 500mcm B,O,Y,Gray, no ground wire. I have rigid conduits coming into the switch gear and need to bond each conduit back to the ground bar. Could I daisy chain each conduit together and hit the ground bar in one location, or would it be recommend to hit each conduit individually back to the ground bar? With both scenarios please share code references so I can understand more about it. Thank you
 
I think this will answer your question

250.102(C) Size — Supply-Side Bonding Jumper.

(1) Size for Supply Conductors in a Single Raceway or Cable.

The supply-side bonding jumper shall not be smaller than specified in Table 250.102(C)(1).
(2) Size for Parallel Conductor Installations in Two or More Raceways or Cables.

If the ungrounded supply conductors are connected in parallel in two or more raceways or cables, the supply-side bonding jumper shall be sized in accordance with either of the following:
  • (1)
    An individual bonding jumper for each raceway or cable shall be selected from Table 250.102(C)(1) based on the size of the largest ungrounded supply conductor in each raceway or cable.
  • (2)
    A single bonding jumper installed for bonding two or more raceways or cables shall be sized in accordance with Table 250.102(C)(1) based on the sum of the circular mil areas of the largest ungrounded conductors from each set connected in parallel in each raceway or cable. The size of the grounded conductor(s) in each raceway or cable shall be based on the largest ungrounded conductor in each raceway or cable, or the sum of the circular mil areas of the largest ungrounded conductors from each set connected in parallel in each raceway or cable.
Click to expand...
 
Much appreciated. Am I reading the table properly? 500kcmil copper requires a 1/0 bonding jumper. What is the reasoning why the bonding jumper is sized that way? It seems a bit overkill. But I have been wrong before.
 
Shane30 said:
Much appreciated. Am I reading the table properly? 500kcmil copper requires a 1/0 bonding jumper. What is the reasoning why the bonding jumper is sized that way? It seems a bit overkill. But I have been wrong before.
Click to expand...
Yes, you need 1/0 if you do each conduit individually to the EG bar. Doing them individually has very different sizing requirements as opposed to daisy chaining. You can't daisy chain them with 1/0. If you daisy chain them you will need a conductor so large it is not practical.
The reasoning for the sizing is that in the event of a ground fault it has to carry the current of unprotected service conductors.
 
Dennis Alwon said:
I think this will answer your question
Click to expand...
Quick comment on posting info copied from NFPA Link:

- The version of the section you posted is the 2023 NEC version; the 2017 and 2020 NEC versions are worded differently (but I don't think it's a change, just an attempt at clarification). Apparently the 2023 NEC is now the default?
- The embedded links to the Table go to NFPA Link pages that aren't accessible with a free account. If you'd like to strip out those links when you copy and paste, you can use "Paste as Plain Text" which for Windows is Ctrl-Shift-V, or you can usually right click and choose Paste as Plain Text.

Cheers, Wayne
 
Thank you for the clarification. Same topic, different scenario. If each of those conduits had thier own ground wire, would I then be able to daisy chain the bond bushings together? Would that now be considered equipment bonding jumper and not supply side bonding jumper?
 
Shane30 said:
Thank you for the clarification. Same topic, different scenario. If each of those conduits had thier own ground wire, would I then be able to daisy chain the bond bushings together? Would that now be considered equipment bonding jumper and not supply side bonding jumper?
Click to expand...
If you are ahead of the service disconnect, it is a supply side bonding jumper.
 
I should have clarified for the last scenario. If I was to run a parallel set of conduits from the switch gear to a load in the field, would I then be able to daisy chain bond bushings. Simply put when is it allowed to daisy chain bond bushings without having to oversize the bond wire.
 
Shane30 said:
I should have clarified for the last scenario. If I was to run a parallel set of conduits from the switch gear to a load in the field, would I then be able to daisy chain bond bushings. Simply put when is it allowed to daisy chain bond bushings without having to oversize the bond wire.
Click to expand...
You are confusing service conductors with feeders. In a feeder this would be an EGC and sized per 250.122. In this case the bonding jumper would be the same if you daisy chained or not.
You need to understand the difference between service conductors and conductors that are protected by an OCPD. Study 250.102 and 250.122.
 
Shane30 said:
I should have clarified for the last scenario. If I was to run a parallel set of conduits from the switch gear to a load in the field, would I then be able to daisy chain bond bushings. Simply put when is it allowed to daisy chain bond bushings without having to oversize the bond wire.
Click to expand...
As Texie said your two questions are asking about two different things and each has it's own specific answer. For ease of finding the answers in the NEC you need to recognize the proper terminology. Your first question is about SSBJ's as Dennis posted and as you have in the thread title. You second question is about bonding jumper sized as EGC's. The answers are vastly different. For the 4000 amp service the separate raceway bonding would be #1/0 for each raceway. For a 4000 amp feeder the bonding jumper for each raceway would be 500 kcmil.
 
Shane30 said:
..rigid conduits coming into the switch gear and need to bond each conduit back to the ground bar. ..
Click to expand...
Myers hubs on both ends of RMC are listed for enclosure bonding to MBJ / grounding bars, and simpler than EGC's.
 
ramsy said:
Myers hubs on both ends of RMC are listed for enclosure bonding to MBJ / grounding bars, and simpler than EGC's.
Click to expand...
As far as we know, the OP is referring tp service raceways. On a service this large the conduits would typically be not attached at either end so Myers hubs have no use here. Even if the conduits terminated at an enclosure and you used a Myers hub it would have to be a grounding type hub, not a standard Meyers hub. Also, the jumpers in question are not EGCs but rather SSBJs.
 
Thanks texie, I see Myers hubs listed for service entrance have those big grounding lugs attached, and STD bonding bushings cost less for metal pipe stubbed in without cabinet contact.

So, does supply side bonding bushings with wire lug jumpers still allow metallic conduit to replace ground conductors?
 
Status
Not open for further replies.
Top