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#195808 - 08/23/10 11:04 PM derating branch circuit wires
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
I have a code question about derating...
If I use #10 on a 20A branch ckt for volt drop purposes, do I have to pull a #10 grounding conductor as well? Or can I still use a #12?

Thanks guys,
H20

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#195809 - 08/23/10 11:20 PM Re: derating branch circuit wires [Re: watersparkfalls]
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
think 250-122(B) requires me to pull a #10 as well, if I am interpreting this correctly... increase size(no reason given I.E. derating for # of cond. in raceway or volt drop.

Is this correct interpretation?

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#195811 - 08/24/10 12:28 AM Re: derating branch circuit wires [Re: watersparkfalls]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
That is the way I read it too.

The only time I see you getting a possible break is if you went from a #10 to a #8 since a #10 is the standard EGC for a #8 (up to 60a)
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Greg Fretwell

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#195812 - 08/24/10 06:29 AM Re: derating branch circuit wires [Re: gfretwell]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
I have to agree with Greg.
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John

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#195813 - 08/24/10 07:56 AM Re: derating branch circuit wires [Re: HotLine1]
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
Thanks

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#195814 - 08/24/10 10:42 AM Re: derating branch circuit wires [Re: watersparkfalls]
mikesh Offline
Member

Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
The Canadian code recently changed to require this. Bonding wires used to be sized according to the breaker or fuse size but this created a problem for long runs where the bond wire would be say #14 but the circuit conductors had to be #6 for VD reasons IE still a 15 amp circuit.
Current rules now size the bonding wire (equipment ground) to the circuit conductor. A very good rule change which the NEC already had that lowered the impedance of the return wire so the breakers or fuses would trip faster.

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#195824 - 08/24/10 03:06 PM Re: derating branch circuit wires [Re: mikesh]
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Hey Mikesh, I think the Canadian Code is the same as the NEC on this but I don't have a copy of the Canadian Code. The NEC requires us to increase the EGC when we increase the ungrounded conductors and they use the word "proportionately". There's an easy way to do that using Table 8 in the back of the NEC.


250.122(B)


Edited by George Little (08/24/10 03:07 PM)
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#195826 - 08/24/10 04:00 PM Re: derating branch circuit wires [Re: George Little]
mikesh Offline
Member

Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
George
Yes the current rules in the 2009 Canadian code does require the bond (equipment ground) wire to be sized according to the circuit wire size and use table 16.
So if the load was 12 amps but it was far enough away to need a bigger wire than #14 then the bond wire must get bigger too.
In the CEC before 2009 the bonding wire never had to get any bigger than #14 because the circuit was connected to a 15 amp breaker and it was the breaker or fuse size that used to determine the bond wire size.
The new way compensates for voltage drop on the bond wire and the old rule did not. So the old way was like adding a resistor to a fault a long way out from the source and did cause longer trip or longer fusing.
I think the NEC has always had this one right and the CEC only just got it right in 2009.

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#195835 - 08/24/10 07:49 PM Re: derating branch circuit wires [Re: mikesh]
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Greg,
Going up in wire size without changing the size of the OCPD will not change anything. If you have a 20 amp breaker, the EGC must be the same size as the ungrounded conductor, no matter how large that conductor is.
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Don(resqcapt19)

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#195839 - 08/24/10 08:38 PM Re: derating branch circuit wires [Re: resqcapt19]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
That is where 250.122 becomes ambiguous. If that is true, you can't upsize using a cable wiring method greater than #8 since once you get to #8, cables have smaller EGCs.
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Greg Fretwell

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