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Re: derating branch circuit wires [Re: gfretwell] #195845 08/25/10 12:54 PM
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resqcapt19 Offline
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Greg,
I don't think the rule is one bit ambiguous. It is clear that when you are using OCPDs rated 30 amps or less that the EGC must be of the same size as the ungrounded conductors. If you are using a cable wiring method, you will have to get custom cable or use a cable 4 conductor cable in place of a 3 or 5 in place of a 4 to get a full size condutor to use as the EGC.

It is my opinion that the size of the EGC should be based on the size of the ungrounded conductor and not on the size of the OCPD. That would make table 250.122 work like 250.66, but that is not what the code says and a proposal to that effect was rejected by CMP 5.


Don(resqcapt19)
2017 / 2014 NEC & Related Books and Study Guides
Re: derating branch circuit wires [Re: resqcapt19] #195848 08/25/10 02:14 PM
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gfretwell Offline
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When you step back and look at the rules in general, it appears this is a "small conductor" rule and once you get to #8 it is not a small conductor anymore but I agree that is what the rules say.


Greg Fretwell
Re: derating branch circuit wires [Re: gfretwell] #195863 08/26/10 11:29 AM
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Yoopersup Offline
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250.122 (B) is quite clear Up the ungrounded conductor because of Voltage drop Upsize the Equipment ground Proportionately according to circular mill area of the conductor. Does not note size Small or large.
Yoopersup
Note: but in no case does the EGC have to be larger then conductor: (250.122 (A)

Last edited by Yoopersup; 08/26/10 11:31 AM.
Re: derating branch circuit wires [Re: Yoopersup] #195866 08/26/10 01:31 PM
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gfretwell Offline
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That does bring up the interesting conundrum that you can have an 8 ga circuit with a 10ga EGC on a 50a breaker but if you put a 30a breaker on it you need an 8ga EGC.
Things that make you say huh?


Greg Fretwell
Re: derating branch circuit wires [Re: gfretwell] #195905 08/28/10 12:32 PM
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renosteinke Offline
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Ambiguouis? Maybe not. Logical? Probably. Consistant? Not a chance.

I woud submit that if a #10 is adequate for 30 amp fault current when voltage drop is not a concern, then that same #10 ought to be adequate for 20 amps when you are worried about voltage drop.

Yet, strictly speaking, that's not how the code reads. This, in turn, leads to the conclusion that many cable wiring methods are not suitable for long runs.

This brings to mind the 'insulated ground' requirement for some pool panels.

These little glitches area direct consequence of the way the NEC is written. Frequent revisions, isolated panels, lobbying interests - and the latest twist, an 'appeals' element. I suppose the real miracle is that there are not more such unicorns in the code forest.

It's something to think about as we prepare to receive a new edition. From the crystal clarity of the Constitution, the NEC is more beginning to resemble the tax code.

Ultimately, it's not about wire sizing.

Re: derating branch circuit wires [Re: renosteinke] #195906 08/28/10 01:11 PM
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Jim M Offline
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Like you said John, not too hard to get inconsistancies when the CMPs are focused on one area and don't see how their change can affect other Articles. Sometimes you need to step back and look at the NEC as a whole.

There are also the ones like you and I have discussed like the cord and plug range hood that needs a dedicated circuit, but if you hardwire it you do not. If you are doing this to allow a possible future change to a microhood you should have the circuit dedicated regardless of connection method. But wait, isn't this a design issue?

Re: derating branch circuit wires [Re: Jim M] #195909 08/28/10 11:23 PM
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Yoopersup Offline
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I really think its Quite Clear (250.122b )
Voltage drop must be taken in account in the GEC as well as phase conductors. Whats unclear about that???

Re: derating branch circuit wires [Re: Yoopersup] #195911 08/29/10 12:53 AM
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gfretwell Offline
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You start getting answers like "No I didn't upsize for voltage drop, it was just what I had on the truck". wink


Greg Fretwell
Re: derating branch circuit wires [Re: gfretwell] #195927 08/31/10 12:56 PM
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resqcapt19 Offline
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Youpersup,
There is no code requirement to take voltage drop into account other than a couple of specific circuits.

250.122(B) no longer mentions voltage drop(that wording was last used in the 1999 code). If you use an ungrounded conductor that is larger than the minimum size permitted by Table 310.16, the you must increase the size of the EGC in direct proportion to the increase in size of the ungrounded conductor.


Don(resqcapt19)
Re: derating branch circuit wires [Re: resqcapt19] #195936 08/31/10 10:59 PM
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Yoopersup Offline
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So if you increase the wire size , Example street light outlets on poles to 1/0 . Equipment ground size does what????
RV parks same as a cpl examples where Much larger phase conductors are used because of VD/

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