Equipment Grounding Conductor

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sybrandy

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In a high ambient temperature environment, do you have to derate the equipment grounding conductor? I would assume so, but wanted to be sure. And also, would you use the 310 charts to derate it? I appreciate any input
 
Equipment Grounding Conductor

The equipment grounding conductor must be increased proportionally to the increase of the ungrounded conducor for the ambient temp increase. NEC 250.122(B). Use table 8 for conductors 4/0 and smaller to apply the proportional increase to the ground conductor.

Marty
 
Why would ambient temperature correction of the ungrounded conductors change the size of the EGC?
 
infinity said:
Why would ambient temperature correction of the ungrounded conductors change the size of the EGC?
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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 the circular mil area of the ungrounded conductors.
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I read this as meaning for any reason.
 
chris kennedy said:
I read this as meaning for any reason.
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I think you are right sir. oops, I called you sir. sorry. :wink:

I believe that heating effects from other conductors in a raceway will also have an affect on the ampacity of a grounding conductor sitting there and not carrying current.

For any reason would be a good addition the that article. :smile:
 
inspector141 said:
The equipment grounding conductor must be increased proportionally to the increase of the ungrounded conducor for the ambient temp increase. NEC 250.122(B). Use table 8 for conductors 4/0 and smaller to apply the proportional increase to the ground conductor.
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I agree. If the ungrounded conductors have to be increased for any reason, the EGC must be increased proportionally to the increase in the ungrounded conductors. You can use Table 8 for all sizes, not just 4/0 and smaller. For example, 500kcmil = 500,000 circular mils.
 
Pierre C Belarge said:
So the question begs, prior to the 2008 NEC, is it a requirement to adjust for ambient temperature?
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I don't have an 05 handy, but.... The increase in the size of the ungrounded conductor has a direct relationship to the fault current in the circuit. Increasing the ungrounded without increasing the grounding....mabey could cause the grounding conductor to fail before the fault clears.

Prior to the 08 if you increased the size of the ungrounded.....you did what to the grounding? Increase it?

Did I answer the question?
 
Not to ignore your question, Pierre, but as to the original question, no, you do not derate the EGC. Never. It does not happen; we do no such thing. Did I say no yet? Nope. Nada. Niet.

Any takers on this challenge? Anyone notice that this is essentially a challenge? :smile:
 
Pierre C Belarge said:
So the question begs, prior to the 2008 NEC, is it a requirement to adjust for ambient temperature?
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Help me understand your point, Pierre. Is it a requirement to adjust WHAT for ambient temperature? :confused: Or did my last post answer this question already? ;)
 
charlie b said:
Not to ignore your question, Pierre, but as to the original question, no, you do not derate the EGC. Never. It does not happen; we do no such thing. Did I say no yet? Nope. Nada. Niet.

Any takers on this challenge? Anyone notice that this is essentially a challenge? :smile:
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If you have to increase the size of a conductor for the load due to derating and are increasing the grounding conductor, is that not derating?
 
frizbeedog said:
If you have to increase the size of a conductor for the load due to derating and are increasing the grounded conductor, is that not derating?
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No, it is not derating. You are on the right track, however.
 
charlie b said:
you do not derate the EGC. Never. It does not happen; we do no such thing. Did I say no yet? Nope. Nada. Niet.
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Granted, but if you derate the ungrounded conductors then the EGC is also increased as per 250.122(B). So in a round about way, derating effects the EGC.
 
chris kennedy said:
Granted, but if you derate the ungrounded conductors then the EGC is also increased as per 250.122(B). So in a round about way, derating effects the EGC.
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I agree. I think. Charlie is toying with us mortals. :wink:
 
chris kennedy said:
. . . .So in a round about way, derating affects the EGC.
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True. But the OP asked about derating the EGC.

You do not ?derate? the EGC, because it was not ?rated? in the first place. EGCs do not have ampacity values assigned.

The size of the EGC is based initially on the overcurrent protection device setting. We do not say that we need an EGC that has an ampacity of 30 amps, then take note that under the prevailing circumstances (e.g., an ambient temperature of 61C) a #10 must be derated to an ampacity of 23 amps, so you need a bigger EGC. Instead, we say that a 30 amp circuit needs an EGC of #10, then take note that under the prevailing circumstances (e.g., an ambient temperature of 61C) a #10 ungrounded conductor must be derated to an ampacity of 23 amps, so you need a bigger ungrounded conductor, and therefore must also get a bigger EGC.

The ampacity of the EGC is never discussed. Indeed the intent of ampacity limitations is to ensure that the heat generated by current flowing in the conductor does not cause damage to the conductor?s insulation system. Well, an EGC might not have any insulation, so you don?t need to derate the EGC to protect its insulation. Also, an EGC never carries current except during the rare and brief events in which it helps clear a fault. So there is no concern about overheating its insulation, even if it had insulation.
 
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