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#195808 - 08/24/10 02:04 AM derating branch circuit wires  
watersparkfalls  Offline
Member
Joined: Mar 2005
Posts: 220
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


2017 / 2014 NEC & Related Books and Study Guides

#195809 - 08/24/10 02:20 AM Re: derating branch circuit wires [Re: watersparkfalls]  
watersparkfalls  Offline
Member
Joined: Mar 2005
Posts: 220
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?


#195811 - 08/24/10 03:28 AM Re: derating branch circuit wires [Re: watersparkfalls]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
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)


Greg Fretwell

#195812 - 08/24/10 09:29 AM Re: derating branch circuit wires [Re: gfretwell]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,872
Brick, NJ USA
I have to agree with Greg.


John

#195813 - 08/24/10 10:56 AM Re: derating branch circuit wires [Re: HotLine1]  
watersparkfalls  Offline
Member
Joined: Mar 2005
Posts: 220
Washington...Not DC
Thanks


#195814 - 08/24/10 01:42 PM Re: derating branch circuit wires [Re: watersparkfalls]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
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.


#195824 - 08/24/10 06:06 PM Re: derating branch circuit wires [Re: mikesh]  
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
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)

Last edited by George Little; 08/24/10 06:07 PM.

George Little

#195826 - 08/24/10 07:00 PM Re: derating branch circuit wires [Re: George Little]  
mikesh  Offline
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Joined: Jun 2006
Posts: 613
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.


#195835 - 08/24/10 10:49 PM Re: derating branch circuit wires [Re: mikesh]  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
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.


Don(resqcapt19)

#195839 - 08/24/10 11:38 PM Re: derating branch circuit wires [Re: resqcapt19]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
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.


Greg Fretwell

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