THIS IS NOT A TRICK QUESTION

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pierre

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Westchester County, New York
I did an inspection for the County today, and came across some engineers who would have preferred to see me buried beneath the concrete that was being poured on the job ;) . Here is the situation/question.

There are two separate buildings that HAVE METALLIC CONNECTIONS between them.
There are 4 PVC raceways with 350 kcmil run in each PVC raceway, being supplied by a 1200 amp OCPD.
The engineers specified 3 AWG sized conductor for the equipment ground conductor. I told them the code required a size ?? AWG equipment ground conductor installed in EACH raceway.

What minimum size equipment ground conductor is required?


By the way - they told me that I had no clue about this and that the 3 AWG is sized fine. They also said a few other things :eek: , but this is not the proper place to repeat them.

Do you agree?
 
Re: THIS IS NOT A TRICK QUESTION

I imagine you pointed out 250.122(F)(1) and the need for a 3/0 copper in each raceway? :cool:
 
Re: THIS IS NOT A TRICK QUESTION

pierre -

First, I have little sympathy for engineers that get in fights with an AHJ. I have an occasional professional disagreement with our AHJ and we sit down with a code book and I explain my reasoning. And if I can't, that says something about my reasoning. And if he tells me I'm in violation, my first question is, "What article? And we go look at it. From what you described, shame on them.

Now to the question:
I don't see how the metallic connection between the two buildings matters. If I missed something here, please jump in.

Assumption: There is a separate 1200A feeder to each building.

So, assuming this is a feeder, there is only one way a #3 in each conduit is reasonable. See 250.122(F)(2). There would have to be ground fault protection set to 310A or less.

If no GFP, then the EGC is sized per Table 250.122 for a 1200A OCP. One in each conduit. No forgiveness for having smaller paralleled conductors. See 250.122(F)(1).

Hard to see how the four conduits and conductors could be a service when it is being fed by a CB. However, if in some way this is considered a service, then there is forgiveness for having paralleled conductors. See 250.102(C). Then T250.66 calls for a #2 in each conduit.

There is there is one other thing I can think of. The NESC scope says it can be applied to a large industrial complex, and the feeders to each building are considered services. I'm not real familiar with the NESC, first time I looked at it was last week. So I don't know if this would matter.

If you get a chance, maybe you could ask for the engineers' references. Tell them you will research it. I'd like to know. I'm always willing to learn.

carl
 
Re: THIS IS NOT A TRICK QUESTION

Morning Carl

Originally posted by coulter:
I don't see how the metallic connection between the two buildings matters. If I missed something here, please jump in.
Click to expand...
The EGC could be forgotten about entirely if there where no metallic paths between the two buildings per 250.32(B)(2) :)


Originally posted by coulter:
Assumption: There is a separate 1200A feeder to each building.

So, assuming this is a feeder, there is only one way a #3 in each conduit is reasonable. See 250.122(F)(2). There would have to be ground fault protection set to 310A or less.
Click to expand...
250.122(F)(2) can only be applied to cables, not raceways.

Originally posted by coulter:
Hard to see how the four conduits and conductors could be a service when it is being fed by a CB. However, if in some way this is considered a service, then there is forgiveness for having paralleled conductors. See 250.102(C). Then T250.66 calls for a #2 in each conduit.
Click to expand...
I can't see how this would be a service however if we say it is a service an EGC is unnecessary and conflicts with 310.4 and possibly other sections.
 
Re: THIS IS NOT A TRICK QUESTION

Good Morning Bob - although just barely here

Originally posted by iwire:
... The EGC could be forgotten about entirely if there where no metallic paths between the two buildings per 250.32(B)(2) :)
Click to expand...
You're thinking there is one service to one building, with a feeder to the other. I took it to mean there were two buildings with a 1200A feeder to each. You are probably right.

Originally posted by iwire:
... 250.122(F)(2) can only be applied to cables, not raceways.
Click to expand...
I thought that too, until I carefully read 250.122(F). It refers to both cables and raceways. And it says either (1) or (2) can be used. Yes I am aware (2) only says "cables".
Before the advent of MC-HL, one had to purchase 4 conductor MC and use one for a grounding conductor. The change to allow a GFP alleviated that.

So if one looks at two installations, one in parallel receways and one in MC cable, why would the MC cable be safe using a GFP and a similar installation in raceways would not? From an engineering standpoint, I can't see there is a difference. I think I could make a credible argument there is no difference and the GFP provision should apply.


Originally posted by iwire:
... however if we say it is a service an EGC is unnecessary and conflicts with 310.4 and possibly other sections.
Click to expand...
You lost me on the conflict with 310.4. Could you explain that one a little more.


My plan is to wait for pierre to repost with a little more information. Then I won't be guessing.


carl
 
Re: THIS IS NOT A TRICK QUESTION

Originally posted by coulter:
Originally posted by iwire:
... The EGC could be forgotten about entirely if there where no metallic paths between the two buildings per 250.32(B)(2) :)
Click to expand...
You're thinking there is one service to one building, with a feeder to the other. I took it to mean there were two buildings with a 1200A feeder to each. You are probably right.
Click to expand...
Either way 250.32(B)(2) could be applied if the conditions where right.

Originally posted by coulter:
Originally posted by iwire:
... 250.122(F)(2) can only be applied to cables, not raceways.
Click to expand...
I thought that too, until I carefully read 250.122(F). It refers to both cables and raceways. And it says either (1) or (2) can be used. Yes I am aware (2) only says "cables".
Click to expand...
I guess we will have to agree to disagree, I do not belive your way of reading that section matches the style manual. I feel that 250.122(F)(2) can only apply to cables even considering 250.122(F) mentions both cable and raceways.

As you mentioned there was a reason cables where given this option, there is no need for that option with raceways.

Originally posted by coulter:
So if one looks at two installations, one in parallel raceways and one in MC cable, why would the MC cable be safe using a GFP and a similar installation in raceways would not? From an engineering standpoint, I can't see there is a difference. I think I could make a credible argument there is no difference and the GFP provision should apply.
Click to expand...
Now you are changing the question. :)

I know Pierre enough to know if he used the terms feeder and EGC that is what he has has.

Going with what I believe Pierre has described I stick by my opinion with or without GFP a 3/0 copper EGC is required in each raceway by the NEC.

JMO, Bob
 
Re: THIS IS NOT A TRICK QUESTION

Bob
Your response is right on the money.
250.122(F)(1) and 250.32

The metallic path keeps me from letting them abandon the EGC and using the grounded conductor. and 3/0 is what I told them the NEC requires as the MINIMUM. See also the note to table 250.122.
300 foot is the length of the installation.

Obviously their concern is the length of time to repair (pull it out, pull it back in), and the cost. They have an official opening in 3 weeks- with the news teams invited :eek: .

I did try to help them find a way to do this without removing the conductors, but it is not easy.
BTW- this is for a public pool with multiple buildings, equipment in all of the buildings.

The engineers and the contractors were yelling at me, I did not raise my voice once - all I had to do was take my pen out and write down the section numbers, as I always do - I believe there is no violation if the inspector does not know the section number of the violation.
I went even further though as there is a meeting today with all parties involved. I copied all of the different references (with illustrations) that I have in my library and made copies for all to observe during our meeting - a little theory never hurts when explaining the code.
 
Re: THIS IS NOT A TRICK QUESTION

I looked at the book, and came up with my answer (3/0), before I read the rest of the replies. (Really, honest! :D ). I was cautious about the ?metallic connections? clue, until I re-read the paragraph about using the neutral in place of the EGC. Then I was sure about that answer.

Now here is a conjecture for you. I?ll not defend the other engineers, and I certainly deprecate their behavior, but I?ll make a ?guess? as to their reasoning. It would be wrong reasoning, but it is one of those ?Oh, I see why you thought that, and I agree that it might seem reasonable, but here is what you apparently missed, and why that reasoning is wrong? situations.

Suppose, just suppose, that they reasoned as follows:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">A 350 MCM copper conductor is good for 310 amps.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">That is higher than 300, so I?ll base the EGC on 400 amps.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">The EGC required for a 400 amp OCPD is a #3.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Therefore, I?ll put a #3 in each of the four conduits, and I?ll have it covered.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
It is not an unreasonable path of reasoning. It is just, sad to say, wrong. So while you are copying your code articles in preparation for the meeting, I suggest that you keep handy a copy of 250.122(D).
 
Re: THIS IS NOT A TRICK QUESTION

Originally posted by pierre:
I did an inspection for the County today, and came across some engineers who would have preferred to see me buried beneath the concrete that was being poured on the job...
By the way - they told me that I had no clue about this and... They also said a few other things :eek: , but this is not the proper place to repeat them.
Click to expand...
Welcome to it, my friend. I told the supervisor of a job today that from this day forward, when I get on the job, he will leave the job within 2 minutes of my arrival. If he doesn't leave, I will leave and not perform the inspection. It's sad to say, but I know enough inspectors (myself included) that have been assaulted or at least threatened.

Be careful, Pierre.

BTW: I agree with Bob 100%
 
Re: THIS IS NOT A TRICK QUESTION

In all the discussion about which section you copy and quote for the engineers to understand the requirements, don't forget the most important section of 250: 250.4. It has a mandatory rule that requires everyone involved to follow all the prescriptive methods in 250. It is based on the collective info gathered and the knowledge of a group of industry experts(aka code panel). It doesn't matter if they(the engineers) have a degree or how many degrees they have, they must still follow all of the rules in 250. 90.4 allows the AHJ to waive specific requirements or permit alternitive methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety. There is none of us who can waive any minimum requirement in 250, we cannot assure that all objectives are met! Yet most of us, myself included, are macho enough to think we can calculate the impepance, determine the amount of fault current that will flow on a given path, match it to an OCD, establish the time it would take to trip, ampacity of the conductor, etc etc and design the grounding system. NO CAN DO!!
We must do as a minimum what 250 prescribes. Thanks for letting me rant about my number one pet peeve - designing a grounding system without using 250 as a minimum standard.
Fred Bender
 
Re: THIS IS NOT A TRICK QUESTION

Originally posted by iwire:
... I guess we will have to agree to disagree, I do not belive your way of reading that section matches the style manual. I feel that 250.122(F)(2) can only apply to cables even considering 250.122(F) mentions both cable and raceways....
Click to expand...
No, we shouldn't have to disagree, and I wouldn't ask you to believe. I am not adbvocating a gfp and a small ebj, rather I was attempting to understand the reasoning. Charlie explained that much better than I did.

Originally posted by iwire:
... Now you are changing the question. :)
Click to expand...
I guessed that :)

Originally posted by iwire:
... I know Pierre enough to know if he used the terms feeder and EGC that is what he has has
Click to expand...
Inexplicably, I eventually guessed this as well. :)

Originally posted by iwire:
... Going with what I believe Pierre has described I stick by my opinion with or without GFP a 3/0 copper EGC is required in each raceway by the NEC.
Click to expand...
Absolutely you should. This is a new installation. The 3/0 answer is patently obvious.

And since the answer seemed obvious, and, Pierre I really don't know you, I really was interested in why the engineering group would advocate a small egc.

carl
 
Re: THIS IS NOT A TRICK QUESTION

Pierre,

I'll bet their next show of superior intelligence will be to tie the 3/0 to the #3 and drag it across the conductors insulation that are still in the conduit. What do you think?
It makes me wonder how long they have been doing this on other projects. This is a lesson that needed to be learned.

frank
 
Re: THIS IS NOT A TRICK QUESTION

I was not trying to teach anyone a lesson, I like to think when I make inspections that I am an advocate of our industry.
Being insulted and yelled at is not too much fun :( , one of the aspects of being an inspector that makes the job disheartening. I try to keep my pride and integrity by not replying (even though there are times....).

The meeting yesterday was interesting, especially the response to the handout I presented, as they never experienced that before.

"I'll bet their next show of superior intelligence will be to tie the 3/0 to the #3 and drag it across the conductors insulation that are still in the conduit."

You are correct, as they are going to attempt this. I requested a megger test if they do succeed, of which I will be there to observe.

Two good things came from this: 1. some people learned a little, 2. The County Commissioner has asked me personally to inspect the next County project - which is quite large :D . Who says there is no justice ;)
 
Re: THIS IS NOT A TRICK QUESTION

Nicely done, Pierre!
icon14.gif


[ April 22, 2005, 07:53 AM: Message edited by: georgestolz ]
 
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