Help, I want to ground all my bond bushings with one wir

[yanert]

I got a call today from a friend that just installed a large service at a commercial building. Seems he just got red flagged for the size of his equipment-bonding jumper for his parallel service conduits. He ran one wire through all the ground bushings on the service conduits.
What he did was take the circ mils of the largest phase conductor in each conduit, add together, took that number and applied it to table 250.66. His circ mils were over 1100. He then took the wording of the table to say, anything over 1100 shall be a 3/0 copper. So he bonded with a 3/0. The inspector told him no and made him multiply the largest phase conductor of each set by 12.5 from 250.28 D. His circ mils where over 1100 for table 250.66. So he went to chapter 9, table 8.

Here are the calcs.
4 rigid conduits.
3-350 phase conductors each conduit.
Each phase, 4 ? 350?s = 1400 circ mils each phase.
Electrician said, over 1100, just use a 3/0
Inspector, multiply circ mils by 12.5 and go to ch. 9 table 8.
1400 circ mils x 12.5 =175,000. 3/0 = 167,800 table 8
Have to use a 4/0. 211,600 table 8

After looking at the code fairly close, it would appear to me that they were both in error. Wouldn?t the rigid conduits be equipment? From what I can tell, they would fall under 250.92 A and 250.102C. It seems to me in my thinking. that you should run a bonding wire to each service conduit and size each bonding jumper to the total circ mils of the phase conductors in that conduit.
3 ? 350?s each conduit, phase wires =1050 circ mils.
Bond each conduit with a 2/0 copper wire.

However, if all the parallel conductors where in the same conduit, you would then take the total CM of all the wires of the same phase, add and then, multiply by 12.5% and get your bonding jumper from table 250.66.

Couple of questions.
I understand that on some parallel installations, we have to go to table 8 of chapter 9 just to find the total circ mills of a conductor. But where does it direct us in the code to use chapter 9 table 8 for actually sizing the bonding wire after a total circ mils has been found? Kind of weird that table 250.66 just says the term over 1100, use a 3/0

Also, What is the size of the grounding electrode conductor?
Again, table 250.66 Note 1.
Add all phase conductors of one phase together and go to table. If this were true, our example would be 1400 cm.
Do we use a 3/0 or do we go to a 4/0?

And the big question, Is the feeder conduits considered equipment in relation to bonding/grounding? I sure think so.

And if so, are we required to run a separate bonding wire to each one? If so, my service equipment won't look near as pretty and I have been doing it wrong for awhile!

Thanks, really interested to get the correct answer

 

[don_resqcapt19]

Re: Help, I want to ground all my bond bushings with one wir

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 12? 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.

A single bonding jumper is not permitted. The code words require that the bonding jumper be run in parallel if the service raceways are run in parallel. Each bonding jumper is sized based on the service conductors in the raceway that is being bonded. The size is based on Table 250.66 so in this case each raceway requires a #2 copper bonding jumper.
Don

[ February 10, 2005, 07:10 AM: Message edited by: don_resqcapt19 ]

 

[iwire]

Re: Help, I want to ground all my bond bushings with one wir

IMO 4/0 would be the minimum required size bonding jumper on the supply side of a service with 1400 kcmils of service conductor per phase.

I do not see any requirement for the bonding jumpers to be separate for each raceway unless they where routed with the raceways.

Here is the NEC section regarding the size of bonding conductors on the supply side of a service.

The best advice I can give is read the section slowly and carefully one sentence at a time. IMO it is packed with information that is easily overlooked or misunderstood.

2002 NEC

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 12? 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.

Now this.....

And the big question, Is the feeder conduits considered equipment in relation to bonding/grounding? I sure think so.

...confuses the issue, are we talking about service conductors or feeders?

The requirements are very different.

 

[iwire]

Re: Help, I want to ground all my bond bushings with one wir

Shoot I was slowly putting together my post and Don already gave the info.

But I see Don and I disagree which worries me.

Don, I take that wording to only require parallel bonding jumpers if they where routed within the raceways or cables. In this case the bonding jumper size will only be required to be sized based on the conductors in that one raceway or cable.

If the bonding jumpers simply go from the bonding bushings to the enclosure IMO one bonding jumper based on the total service conductor size is permitted.

Edit poor grammar

[ February 10, 2005, 07:42 AM: Message edited by: iwire ]

 

[cpal]

Re: Help, I want to ground all my bond bushings with one wir

I Apologize but "Like IWIRE" I do not believe that paralleled bonding conductors are required (in this case) for service raceways on the supply side of the service.

I do believe that this could use an official interpretation.

My opinion is base upon the 1986 TCR Proposal 5-130 Log # 1163.

The original substantiation specifically discussed paralleling conductors when routed with the parallel service entrance conductors . The language in the present Code as Bob mentioned reflects that. There is no compelling language that I see to disallow the use of a single conductor properly sized to bond parallel raceways at the Service Equipment.

Charlie

 

[yanert]

Re: Help, I want to ground all my bond bushings with one wir

sorry guys. In my post,

And the big question, Is the feeder conduits considered equipment in relation to bonding/grounding? I sure think so

I should have typed, service conduits!

 

[yanert]

Re: Help, I want to ground all my bond bushings with one wir

I just dug around and found a practice question from Mike Holt.

If a service conists of paralled 400 Kcmil conductors routed in seperate raceways, what size bonding jumper would be required for each service raceway?
1 awg
1/0
2/0
3/0
answer in book is 1/0
It does not give text in the answer, But... It would appear that in the wording of the question, it would take two bonding wires. Also, Don how do you come up with a #2?

 

[iwire]

Re: Help, I want to ground all my bond bushings with one wir

IMO Don's answer of 2 AWG is correct when running a separate bonding jumper within each parallel conduit or cable.

Each conduit has a 350 kcmil service conductor, Table 250.66 shows 2 AWG GEC for 'Over 3/0 through 350' service conductors.

IMO, you really have to read 250.102(C) again and again it has all the answers to your question.

No big deal about the feeder conduit, I just wanted to be sure we where talking service bonding.

Bob

 

[yanert]

Re: Help, I want to ground all my bond bushings with one wir

Iwire,

How about the application of Table 8, chapter 9. When do we apply this for finding the largest Circ mils in the answer to sizing a wire. The whole over 1100cm question in Table 250.66. If in any grounding problem where the circ mils is above 1100 after applying all factors, do we go to table 8? 250.66 says the size of the grounding electrode conductor of a grouned or ungrounded ac system shall not be less than given in Table 250.66 except as permiteed in 250.66 a through C. Also you have note 1 of table 250.66.

In one of my reference books i have this problem.
three 600kcmil conductors installed per phase for a three phase, four wire service.
What is the size of the electrode grounding conductor?
3x600 = 1800
1800 over 1100 so just use a 3/0
It then says, table 250.66 the bottom line under copper indicates that service entrance conductors over 1100 kcmil are not required to bigger than 3/0.
Were in the code is the difference. For a bonding jumper, we went to the table Table 8. For a grounding electrode we just stayed with a 3/0 for the the table 250.66.
I am fine with doing this, i just want to know where it says when we apply it, and when we don't.
Also, would we all agree that the conduits that are used to bring in the service conductors, (service conduits) are in fact equipment, and we use 250.102 rules to apply bonding jumpers?
Thanks!

 

[necbuff]

Re: Help, I want to ground all my bond bushings with one wir

It is permitted to install the bonding jumpers in series (daisey chain) or in parallel. If you choose to parallel you must size the jumper by the largest phase conductor in that raceway using 250.66. If you choose to daisey chain you must multiply the largest service conductor by the number of sets in parallel ie; 350 x 4 in your case. If the final total is over 1100 kcmil copper of 1750 Al , you must multiply that number by 12.5%, this totaling 175,000 kcmil. According to chapter 9 table 8, the required bonding jumper is a 4/0. In reference to the 3/0 max in 250.66, that is for grounding electrode conductors. Bonding jumpers and neutrals are sized as described. Ref 250.24 (c)(1), 250.28 (d), 250.102 (c). A number 2 copper is permitted for the described scenerio if installed in parallel.

[ February 10, 2005, 05:42 PM: Message edited by: necbuff ]

 

[crossman]

Re: Help, I want to ground all my bond bushings with one wir

Yanert:

The 3/0 maximum requirement only applies to Grounding Electrode Conductors. It is my understanding that this is because the earth has a limited ability to carry current and a 3/0 will be sufficient to carry any current likely to be flowing into the earth through the electrode.

Grounded Conductors at the service, Main Bonding Jumpers, System Bonding Jumpers, and Bonding Jumpers on the supply side of the service are sized by 250-66 but if they go off the chart, you use 12.5 percent. Please see 250.24(C)(1), 250.28(D), and 250.102(C). (2005 code)

Additionally, the grounded conductor may have to be larger than what is required in Article 250 because it also has to be sized according to the calculated load as in Article 220.

[ February 10, 2005, 05:52 PM: Message edited by: crossman ]

 

[yanert]

Re: Help, I want to ground all my bond bushings with one wir

crossman, from your quote:
"The 3/0 maximum requirement only applies to Grounding Electrode Conductors. It is my understanding that this is because the earth has a limited ability to carry current and a 3/0 will be sufficient to carry any current likely to be flowing into the earth through the electrode"

I sure wish they would just come out and say it somewhere.

 

[kiloamp7]

Re: Help, I want to ground all my bond bushings with one wir

yanert - "They" are not going to come out & say it like that. "They" are not going to tell you why.
That is not the purpose of the NEC. It is not a training manual.

 

[yanert]

Re: Help, I want to ground all my bond bushings with one wir

Hi Kiloamp
I never asked why. What I was really wanting was just a hard statement. I know I am fighting city hall, but it would appear that many, many people have not applied the correct calculation. Anyhow, let me think about it a bit more and see if I can find a couple of statements in the NEC concerning this. My thoughts are concerning statements like, "do not exceed, or the term shall not exceed. Keep in mind, I am talking about the calc for table 250.66 with the statement, "over 1100" applied to a total circ mil calculation on a grounding electrode conductor vs a bonding jumper. When does over l100 mean just that, If your calc is over 1100, use a 3/0. Also, I guess your statement would mean to say, any electrician using the code should have the sense to understand the concept of what the electrode grounding conductor does and apply it to table 250.66 VS what a bonding jumper does in relation to fault current and then apply it to the statement in 250.66. For the training manual, I agree, but as far as this example I don't agree with you. Also, just by looking at the post, you can tell that others find the wording a little wordy.

 

[kiloamp7]

Re: Help, I want to ground all my bond bushings with one wir

yanert - All I was doing was commenting on your sentence:"I sure wish they would come out & say it somewhere". I was not implying anything at all.

Now with the business at hand; Assume question is dealing with bonding on supply side of service. If that is so, then 250 Part V applies.
250.102(C) is applicable & says not smaller than Table 250.66 (which is maybe most frequently used for GEC). But anyway, if larger than 1100KCMIL, then 12.5%.

I would say that if this is the application that I have assumed, then the equipment
bonding jumper from bonding bushing to bonding bushing would need to be 4/0.

 

[necbuff]

Re: Help, I want to ground all my bond bushings with one wir

Yanert,

I agree that it can get confusing, but it does say what you are asking. These references will answer your question........ 250.24(C)(1) for grounded (neutral) conductors, 250.28(D) for main bonding jumpers, 250.66 for GROUNDING ELECTRODE CONDUCTORS, 250.102(C & D) for equipment bonding jumpers. It is important to note a full understanding of article 100 definitions is a must so that the proper article is applied. Mainly, don't take anything personal in this site. There are some of the best code experts in the world in here and I would bet anyone here would bend over backwards to help you with a problem. While I may not post here daily, I look at this site VERY often to survive in this field and learn from the best. And who knows, maybe someone got something out of one of my post. If we work together we can make the industry better and safer.

[ February 11, 2005, 11:40 PM: Message edited by: necbuff ]