Service Conduit Bonding - ECN Electrical Forums

Recently, an inspector wanted to turn us down for incorrectly bonding metal service conduits. We ran a 3/0 bare copper through the grounding bushing lugs of 8 conduits, then landed the ground wire. Inspector said that 250.102(C) requires each conduit to be bonded independently, not daisy-chained. If they are to be daisy-chined, then the ground wire must be increased to equal the sum of all of the conduits. Sounds crazy and I can't get that out of the text. Has anyone else run into an inspector with similar views?

The inspector knows their stuff.

Part of 250.102(C)

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Where the service-entrance conductors are paralleled in two or more raceways or cables, the equipment bonding jumper, where routed with the raceways or cables, shall be run in parallel. The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.

It makes sense, if a ground fault happens in one raceway the fault current will be coming at the fault through both directions.

No, I don't see it that way. From the opening post, It seems to me that the bonding jumper in question is not being routed "with" the conduits, but merely "to" the conduits. The fault path that runs "with" the conduits is the conduit itself. The largest bonding jumper ever required by table 250.66 is 3/0. In my opinion, if individual bonding jumpers were to be run to each conduit, and if the equivalent conductor size in each conduit were 1100 kcmil or less, then there might be an argument for using the section of code that iwire quoted to downsize those jumpers to something less than 3/0.

Notice the significant differance in sizing rules for parallel conduits on the line side of the disconnect as opposed to section 250.122(F)(1) for conductors on the load side of the disconnect.

I will give it another shot. [Linked Image]

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250.102(C) Size — Equipment Bonding Jumper on Supply Side of Service. The bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors. Where the service-entrance phase conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the bonding jumper shall have an area not less than 12½ percent of the area of the largest phase conductor except that, where the phase conductors and the bonding jumper are of different materials (copper or aluminum), the minimum size of the bonding jumper shall be based on the assumed use of phase conductors of the same material as the bonding jumper and with an ampacity equivalent to that of the installed phase conductors. Where the service-entrance conductors are paralleled in two or more raceways or cables, the equipment bonding jumper, where routed with the raceways or cables, shall be run in parallel. The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.

The bonding jumper for a grounding electrode conductor raceway or cable armor as covered in 250.64(E) shall be the same size or larger than the required enclosed grounding electrode conductor.

This is how I see it, if you run separated bonding conductors for 'each raceway' each of those conductors will be sized based on just that one raceway.

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The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.

However if you daisy chain them nothing changes the bonding jump still has to be based on the size of the service-entrance conductors in each raceway or cable.

Not separately all of them, with them daisy chained you will have count all eight sets of conductors add them up and use that figure with 250.66

Bob

Latest edition of Soares agrees w/iwire.
So do I.

Ok, now that I understand better what iwire is saying, I agree as well. That is why I said that if seperate bonding jumpers were run to each conduit, there may be an argument for downsizing the jumper to something less than 3/0. I guess we need to know what size phase conductors are in each conduit.

Daisy chaining on the supply side is not even an option. Compare carefully the language of 250.102(C) and 250.102(D) (second paragraph). You will see that (C) gives no such allowance.

Ryan I respectfully disagree, I do see the difference in language but I do not see that anything in 250.102(C) prohibits daisy changing.

Bob

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Originally posted by jes Latest edition of Soares agrees w/iwire.
So do I.

I concur also.
[Linked Image]

How is the bonding jumper installed in parrallel when there is only one?

Ryan

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How is the bonding jumper installed in parrallel when there is only one?

It isn't and does not have to be.

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Where the service-entrance conductors are paralleled in two or more raceways or cables, the equipment bonding jumper, where routed with the raceways or cables, shall be run in parallel.

I am talking about a bonding jumper that does not leave the enclosure.

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Originally posted by OVES:
Inspector said that 250.102(C) requires each conduit to be bonded independently, not daisy-chained. If they are to be daisy-chined, then the ground wire must be increased to equal the sum of all of the conduits. Sounds crazy and I can't get that out of the text. Has anyone else run into an inspector with similar views?

He is correct in that the bonding jumper must be larger than 3/0 if the phase conductors are larger than 1100 kcmil, however nowhere in 250.102(C) does it say that you can't daisy chain the bonding conductor. Nor does it say that if you do "then the ground wire must be increased to equal the sum of all of the conduits. What it does say is this: The bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors. Where the service-entrance phase conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum,the bonding jumper shall have an area not less than 12½ percent of the area of the largest phase conductor.

You could theoretically have multiple conduits with a total of less than 1100 kcmil and then size that bonding jumper directly from table 250.66 even though it's being daisy chained through all of the bonding bushings. It's the total circular mils that determines sizing, not the fact that you've daisy chained it.

[This message has been edited by Mvannevel (edited 09-15-2005).]

[This message has been edited by Mvannevel (edited 09-15-2005).]

nothing in 250.102 (C) prevents you from installing one bonding jumper for parallel
raceways or one from each raceway, 250.102 (D) is load side bonding and has nothing to do with 250.102 (C), if you want to install one bonding jumper from each raceway it is sized on largest phase conductor in that raceway, or one for all parallel raceways is
sized on the largest phase conductor, so if you have 4 500kcmil parallel, one bonding for all raceways would be 12 1/2 of 2000kcmil, if this is load side go to 250.102 (D) & table 250.122 and it is sized for the largest overcurrent device.