More on upgrading ECG's

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Re: More on upgrading ECG's

Originally posted by james wuebker: iwire, I did read 250.122(B) and we must remember the word proportionately.
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I think I see the source of confusion here. It seems than you are trying to make the proportion in terms of the ampacity values that are listed in the tables. What is required is that the proportional increase in EGC be in terms of cross-sectional area. If you double the area of the phase conductor, you double the area of the EGC.

This is an easy math problem, when you start with a phase conductor (e.g., #12) that is the same size as the EGC (also a #12). Whatever you do to the phase conductor (e.g., increase to #8) you must also do to the EGC (also must be #8). That is the 1:1 ratio that infinity mentioned.

It becomes trickier when you start with unequal sizes of phase and EGC. For example, start with a 60 amp circuit, using a #6 phase conductor and a #10 EGC. Now increase the phase conductor to #4, and size the EGC. You actually have to look up the circular mil areas of all the conductors, in order to get the proportion right.

(I will leave this as a homework problem. I haven't had enough coffee yet this morning to figure it out myself. :D )
 
Re: More on upgrading ECG's

I have a question

Under Art.250.122 size of Equipment Grounding Conductors.

(B) Increase in size, says to increase in size to your ungrounded conductors.

(C) Multiple circuits,Says size according to your breaker.

The definition of (C) meets the situation just as good as (B).


Both have the word shall in there sentence why would (B) carry more weight than (C)?

Ronald :)
 
Re: More on upgrading ECG's

It doesn't. You do them both. First you size the EGC per your overcurrent device. Then if you use a larger phase conductor, you increase the size of the EGC.

The NEC is not a design manual, and it doesn't have to read like one. It is not out of line for us to have to take step (C), and then go back and take step (B).
 
Re: More on upgrading ECG's

Charlie

You are right it is not an instruction manual I said that from day one.

The reason I went to trade school and you went to a Eng. school is to learn to use the tools and knowledge of our trade and to make decisions like this. I read your post daily you are brilliant in your field, but we see this one different. :)
 
Re: More on upgrading ECG's

Originally posted by ronaldrc:
In Art.250.122 (B) the reason it says to up size your equipment ground with your ungrounded conductors was mainly because of voltage drop.
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I take it you are looking at 1999 NEC?

1999 NEC
250-122. Size of Equipment Grounding Conductors

(b) Adjustment for Voltage Drop. Where conductors are adjusted in size to compensate for voltage drop, equipment grounding conductors, where installed, shall be adjusted proportionately according to circular mil area.
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If your area is still using the 1999 NEC I agree that you would not have to increase the EGC when the ungrounded conductors are increased for derating reasons.

But all that changed with the 2002 NEC.

250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.
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No more talk about voltage drop, use larger wire because that is what you have on the truck and the EGC has to increase as well.

Ronald all the points you brought up about heating and derating etc I fully agree with.

IMO you are right on the money with the physics of this.

However the way the rule is written none of that matters.

It is written simply and plainly.

Increase one and you must increase the other by the same ratio.

It does not have to make sense....it's just the code. :D
 
Re: More on upgrading ECG's

Thanks Bob

No it is the 2002 code and I agree with you 100 percent that is the reason I said I would reluctantly pull a #8 in to replace the #12.

The code is just a little contradictory here. What about (C)? :)

[ October 12, 2005, 04:47 PM: Message edited by: ronaldrc ]
 
Re: More on upgrading ECG's

By the way I heard a rumor on these forums that the change from 99 to 02 was because when inspectors tried to enforce the rule as written in 99 contractors simply said that they did not increase the wire size for voltage drop reasons. They would say they increased the wire size because they had extra of whatever size they ran. :D
 
Re: More on upgrading ECG's

Originally posted by ronaldrc:
The code is just a little contradictory here. What about (C)? :)
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I don't find that part contradictory for the same reasons Charlie stated. :)

'C' would be the starting point and 'B' would be where you may have to go from there if you had increased size ungrounded conductors.

Leave the EGC out and use the raceway, then all this goes away. :)
 
Re: More on upgrading ECG's

Originally posted by ronaldrc:
Bob I like the idea of using the conduit as Eq. Grd. :D but I couldn't get away with it here and you probably couldn't either.
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Why not? It's allowed. :confused:
 
Re: More on upgrading ECG's

Originally posted by iwire:
For me a copper EGC is a job specification 99% of the time. (OK I picked 99 out of the air, but most times) :D
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Yeah, I know. But given a choice and some serious "value engineering," you would do it, right? :D

[ October 12, 2005, 06:01 PM: Message edited by: peter d ]
 
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