250.122(b)

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If I recall, and at my age that is suspect, it has to do with the change in impedance of the un grounded conductor and the available fault currents increasing as a result would exceed the ground conductors abality to help clear the fault.

Please correct me if I am wrong.
 
Johnmcca said:
If I recall, and at my age that is suspect, it has to do with the change in impedance of the un grounded conductor and the available fault currents increasing as a result would exceed the ground conductors abality to help clear the fault.

Please correct me if I am wrong.
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Actually (as I am blowing the cob webs out) that is what Bob explained at one time. Thanks John.

Note Bob I remember you saying that a year or so ago. Heck don't worry I can't remember what I did 5 minutes ago.:)
 
Johnmcca said:
You did better than I could remembering the time frame. I just barely remembered the reason.
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Strange I can remember something that far back but for the life of me I cant remember short term.....oh well retirement is only a few years away....Thank Heavens:grin: Good talking with you John.
 
For my part, I don?t think 250.122(B) is a good rule. It makes no sense to me. If you make the ungrounded wire size bigger, then more fault current would flow. Why do you need even more fault current to flow (the result of also making the EGC bigger)? I tend to doubt that the additional fault current might be too much for the ?normal? size EGC to handle, that the EGC might fuse (open circuit) before the breaker has a chance to trip, and that you need a bigger EGC just to protect the EGC itself. I don't know if that was the actual, original intent for the addition of this rule, nor do I know for certain when the rule was first put into the code. I just know that the wording is confusing, and that the CMP turned down my proposal to get it clarified. :roll:
 
Johnmcca said:
Charlie I agree with you. The sizing of the egc does not follow a lgical progression. Proportionately getting smaller as the currents get larger makes little sense.
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Well back in the day they did allow smaller EGCs for 15, 20 and 30 amp circuits but I had heard that became an issue with people using these EGCs as circuit conductors.

I have also read that the instantaneous trip of all breakers from 15 to 100 amps is virtually identical.
 
dcspector said:
Strange I can remember something that far back but for the life of me I cant remember short term.....oh well retirement is only a few years away....Thank Heavens:grin:
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Look at the bright side. You'll soon be able to the same movie more than once and enjoy it like the first time again.
 
I just checked the handbook commentary and although I didn't find anything for Greg, I found the following. I always like to say; "The EGC must be increased in size even if your reason for increasing the size of the ungrounded conductor is thats all you had on the truck."

This is interesting commentary.

Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch-circuit overcurrent devices ahead of them. Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, the equipment grounding conductors must be increased proportionately.
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Another good example of why the handbook is not enforceable. The red commentary contradicts the language of the code itself. Thanks for pointing that one out, Chris.
 
Here is some info ..I think you will recognize the guy who wrote it.

http://www.iaeiofutah.com/Articles/TheEffectsOfVoltageDrop.pdf


And here is the proposal, I removed the language he wanted stricken

5- 264 - (250-122): Accept
SUBMITTER: Jamie McNamara, Hastings, MN
RECOMMENDATION: Revise to read as follows:
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.

SUBSTANTIATION: The current text is limited to voltage drop
only and is subject to abuse and misinterpretation (e.g. it was
done per the plans, not for voltage drop). The manufacturers
directions often call for conductor to be increased in size, with
no explanation for why the ungrounded conductors size is
increased, with no corresponding requirement for the equipment
grounding conductor to be increased.
PANEL ACTION: Accept.
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There was one neg. vote for a crappy substantiation

so ,...then at the ROC ,. this was the only comment I could find?... I'm a bit surprised that the cable folks did not argue for some sort of exception. This was kind of a big change and there was very little discussion



5- 155 - (250-122(b)): Accept
SUBMITTER: Jamie McNamara, Hastings, MN
COMMENT ON PROPOSAL NO: 5-264
RECOMMENDATION: The panel should continue to support this
proposal. It helps to clarify the requirement.
SUBSTANTIATION: In the Report on Proposals the strike
through text showed up as italic text and should have looked like
this.

250.122(b)
Increased in size
Adjustment for Voltage Drop.
Where ungrounded conductors are
increased adjusted in size to
compensate for voltage drop, equipment-grounding conductors,
where installed, shall be
increased in size adjusted proportionately
according to circular mil area
of the ungrounded conductors.
PANEL ACTION: Accept.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 16
VOTE ON PANEL ACTION:
AFFIRMATIVE: 16
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chris kennedy said:
I just checked the handbook commentary and although I didn't find anything for Greg, I found the following. I always like to say; "The EGC must be increased in size even if your reason for increasing the size of the ungrounded conductor is thats all you had on the truck."

This is interesting commentary.

Quote:
Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch-circuit overcurrent devices ahead of them. Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, the equipment grounding conductors must be increased proportionately.
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Wait a minute. Just because that's all you had in your truck doesn't mean it's related to proper circuit operation.
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