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#190644 - 11/28/09 04:54 PM NM Cables With Reduced EGC.  
KJay  Offline
Joined: Nov 2007
Posts: 763
So as not to completely hijack an existing thread, Iím posting this as a new topic for discussion.
Itís not clear, at least to me, that for an existing installation 250.140, 250.140, Exception and the related articles actually reference or lead to Table 250.122 for equipment-grounding conductor sizing as for all new branch circuit installations.
What are your opinions on this?

Original thread from "Dryer Wiring Question" in the General Discussion Forum:

How would you handle an old style 10/3 NM with reduced equipment-grounding conductor when upgrading from three-wire to four-wire dryer receptacle?
Would you run a new 10/3 NM branch circuit with a full size equipment-grounding conductor or use the existing 10/3 NM, keeping in mind that the new 4-wire receptacle has terminals rated for #10 to #4 AWG wire.

I know Iíve connected the old 14/2 and 12/2 NM with reduced grounding conductors to the grounding terminals of 15A 3-wire duplex receptacles during replacement before, without really thinking about how the minimum size wire rating on the device terminals is #14 AWG.
I guess in actuality, a pigtail could be used to comply here.

2017 / 2014 NEC & Related Books and Study Guides

#190645 - 11/28/09 05:12 PM Re: NM Cables With Reduced EGC. [Re: KJay]  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
KJ, you've hit on one of the main advantages pipe has over cable; you can replace the wire without tearing the walls apart!

I agree that simply using a wire nut to attach a #10 pigtail to a #12 ground wire is the choice solution.

I think it comes down to not letting the 'best' become the enemy of 'good enough.'

#190647 - 11/28/09 08:50 PM Re: NM Cables With Reduced EGC. [Re: renosteinke]  
KJay  Offline
Joined: Nov 2007
Posts: 763
I even went pawing through the '08 Handbook to see if maybe there was some mention or clarification on this, but couldn't find anything.
I'm a little surprised that there is no mention of this particular situation, which I would imagine an EC doing Resi service work must come across at least occasionally in the field.
If it were just a short NM cable run in an open basement, I guess replacement of the cable wouldnít be that big of a deal, but if it were a second floor area or something similar, then we're talking major work.
I suppose if you snip off the grounding conductor, frown then technically it is not "present in the outlet or junction box" as stated in 250.140 Exception, so you could keep the three-wire receptacle configuration using the grounded conductor to ground the dryer frame.

Apparently, it seems that it comes down to a judgment call as to which method is considered safer and more compliant, since for the last ten years or so, the NEC has been steering us away from using the grounded conductor for this purpose.

#190656 - 11/29/09 01:38 AM Re: NM Cables With Reduced EGC. [Re: KJay]  
sparkyinak  Offline
Joined: Jul 2007
Posts: 1,328
It is a judgement call and no one will back you on it. You go to an older house you replace a recept on NM with the under size ground. Rule of thumb is that it doesn't matter what code it was wired under, when you put it back together, it has to meet today's standards. How do you tell the customer that you can not use the old wire? Who is going to back you with the customer? Who is going to back you if it fails by no act of your own? It's a case of damn if you do, damn if you don't.

I would suggest to anyone that if they are not sure what to do, talked to the AHJ.
I typically identify the problem, recommend that it gets replace that usually goes no where and include my comments with the bill. Gotta CYA.

"Live Awesome!" - Kevin Carosa

#190677 - 11/29/09 11:42 PM Re: NM Cables With Reduced EGC. [Re: sparkyinak]  
KJay  Offline
Joined: Nov 2007
Posts: 763
Sparky, I'm not sure how changing a receptacle on an existing installation negates the listing of all other material and equipment connected to the circuit that was originally installed according to the manufactures instructions as well as the NEC at the time and is still functioning as intended.
I don't necessarily see that installed listed products or materials have an expiration date.

With add-ons and extensions from existing circuits... now here is where I am in agreement that the entire circuit must be updated to the current NEC.

#190678 - 11/30/09 01:00 AM Re: NM Cables With Reduced EGC. [Re: KJay]  
sparkyinak  Offline
Joined: Jul 2007
Posts: 1,328
Here is how I see it, you diconnected the wire. In order to for the receptacle to work properly, you have to reconnect the wire. Are they wires properly sized? As mentioned the NEC does not touch this likely because it would gutting a house just to replace a receptacle. At the same time the ground wire is your seatbelt in an electrical accident. Will it save your life? If there was PR on this like there is for AFCI breakers, you best believe they would get it into the code. Its funny how articulate the NEC is when it comes to grounding but really generalize on this and using FPN's for references.

If you extend a 14/2 circuit with 14/2 and you discover there is a 20 Amp breaker feeding the circuit? what are you going to do?

"Live Awesome!" - Kevin Carosa

#190701 - 12/01/09 12:11 AM Re: NM Cables With Reduced EGC. [Re: sparkyinak]  
KJay  Offline
Joined: Nov 2007
Posts: 763
Originally Posted by sparkyinak

If you extend a 14/2 circuit with 14/2 and you discover there is a 20 Amp breaker feeding the circuit? what are you going to do?

That's basically what I was driving at. Here in my state, if you add to or extend an existing circuit, that is considered a new installation and the entire circuit must now be brought up to the current NEC, meaning proper wire size, OCP, AFCI and/or GFCI protection, where required, etc...

But, for existing circuits, you are required to use replacement materials that meet the current code, such as, using TR replacement receptacles for resi, GFCI protected receptacles where required, WP in-use covers where required, etc... but not required to bring the rest of the wiring up to current code.
Although, I'm not sure if you could actually replace an existing two-wire receptacle with a new two-wire TR receptacle, since I donít think any are available at this time.
I guess maybe in this situation you would need to use three-wire receptacles with no equipment-grounding conductor and GFCI protection.

#190706 - 12/01/09 02:38 AM Re: NM Cables With Reduced EGC. [Re: KJay]  
Tesla  Offline
Joined: Jun 2004
Posts: 1,273
Sacramento, CA

Means I'm swapping to a down sized breaker.

Problem solved.


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