If service entrance conductors are paralleled, is the size of the equipment bonding jumper on the supply side of the service equipment (per 250.102(C)) based on the size of the equivalent sum of the paralled conductors, or is it sized based on the size of the individual conductors in the group?
Supply Side Bonding
- Thread starter daverz
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- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Supply Side Bonding
As I read 250.102(C), the rule is (1) You need to run a bonding jumper in each of the parallel ducts, and (2) The size of the bonding jumper in each duct is based on the phase conductors that are in the same duct. But since the paralleled phase conductors are the same size in each duct, the bonding jumpers will be the same size in each duct as well.
As I read 250.102(C), the rule is (1) You need to run a bonding jumper in each of the parallel ducts, and (2) The size of the bonding jumper in each duct is based on the phase conductors that are in the same duct. But since the paralleled phase conductors are the same size in each duct, the bonding jumpers will be the same size in each duct as well.
dana1028
Senior Member
- Location
- San Francisco Bay area
Re: Supply Side Bonding
The bonding jumper is based on the size of the equivalent sum of the paralled conductors .... I think Note 2 ('99) or Note 1 ('02)of Table 250-66 is the code section that addresses this.
The bonding jumper is based on the size of the equivalent sum of the paralled conductors .... I think Note 2 ('99) or Note 1 ('02)of Table 250-66 is the code section that addresses this.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Supply Side Bonding
What I then did, however, is re-read the last couple sentences in the first paragraph in 250.102(C). They appear to contradict the earlier conclusion, and led me to the answer that I posted above. Perhaps this same apparent contradiction is what led Dave R to ask the question in the first place?
Any other thoughts on this one?
That?s what I thought when I first read the question, and first looked at Table 250.66 and its notes. But I think there is room for confusion here. 250.102(C) starts by saying that the size of the bonding jumper is based on that of the EGC. You go to 250.66 and you see that the EGC is based on the total area of all paralleled service conductors. That leads to your answer, and I can?t say that it is wrong.
What I then did, however, is re-read the last couple sentences in the first paragraph in 250.102(C). They appear to contradict the earlier conclusion, and led me to the answer that I posted above. Perhaps this same apparent contradiction is what led Dave R to ask the question in the first place?
Any other thoughts on this one?
dana1028
Senior Member
- Location
- San Francisco Bay area
Re: Supply Side Bonding
Charlie - I agree with you (and so does Note 1 BTW) - I was just reading the question a little differently for my reply. I do think 250.102(C) is quite clear in differentiating between the two types of installations.
Charlie - I agree with you (and so does Note 1 BTW) - I was just reading the question a little differently for my reply. I do think 250.102(C) is quite clear in differentiating between the two types of installations.
Re: Supply Side Bonding
Thank you for your replies. Still uncertain however, I contacted the NFPA for clarification.
Basically, the method used to determine the size of the bonding jumper is dependant on whether the bonding jumper itself will be installed as a single conductor or paralleled. My original question specified that the service conductors were parallelled but I did not address how the bonding jumper would be installed. Apparently, this makes a difference.
Thanks again. Here's the "unofficial" NFPA response.
Dave:
Section 250.102 provides the rule for Equipment Bonding Jumpers. 250.102(A) gives the material type and method. 250.102(C) provides the rule for sizing the conductor(s)on the supply side of the service.
Sizing is done based on the cumulative amount of the service entrance conductors. Up to and including 1100 kcmil copper and 1750kcmil AL, the size is based on Table 250.66. If all phase conductors when added together exceed those defined values in 250.66, then the total amount is multiplied by 12.5%.
For example: 4 sets of 500 kcmil copper conductors are used for a service. This means 2,000,000 cir mils for A, and B and C phase. 2,000,000 X 12.5% is 250,000 cir mils for a single bonding conductor connected to each conduit end and then connected to the grounded conductor terminal bar.
You are also allowed to use 4 individual conductors, based on the size of the phase conductors in each conduit raceway. In this type of application, 500 falls between 350--600 kcmil. This requires you to use one 1/0 copper conductor, and connect it to each of the four separate raceways, the other end connected to the grounded conductor terminal bar.
In summary, the answer to your question is yes for both methods. Neither method is wrong, one could simply be easier to work with in small confined enclosures. I hope this satisfies your questions and concerns.
Thank you for your replies. Still uncertain however, I contacted the NFPA for clarification.
Basically, the method used to determine the size of the bonding jumper is dependant on whether the bonding jumper itself will be installed as a single conductor or paralleled. My original question specified that the service conductors were parallelled but I did not address how the bonding jumper would be installed. Apparently, this makes a difference.
Thanks again. Here's the "unofficial" NFPA response.
Dave:
Section 250.102 provides the rule for Equipment Bonding Jumpers. 250.102(A) gives the material type and method. 250.102(C) provides the rule for sizing the conductor(s)on the supply side of the service.
Sizing is done based on the cumulative amount of the service entrance conductors. Up to and including 1100 kcmil copper and 1750kcmil AL, the size is based on Table 250.66. If all phase conductors when added together exceed those defined values in 250.66, then the total amount is multiplied by 12.5%.
For example: 4 sets of 500 kcmil copper conductors are used for a service. This means 2,000,000 cir mils for A, and B and C phase. 2,000,000 X 12.5% is 250,000 cir mils for a single bonding conductor connected to each conduit end and then connected to the grounded conductor terminal bar.
You are also allowed to use 4 individual conductors, based on the size of the phase conductors in each conduit raceway. In this type of application, 500 falls between 350--600 kcmil. This requires you to use one 1/0 copper conductor, and connect it to each of the four separate raceways, the other end connected to the grounded conductor terminal bar.
In summary, the answer to your question is yes for both methods. Neither method is wrong, one could simply be easier to work with in small confined enclosures. I hope this satisfies your questions and concerns.
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