Older NM cable with reduced size and insulated ground

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JoeNorm

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Looked at a dryer circuit today the the customer wants extended and was pleased to find it was a four-wire. But it had an insulated EGC that appeared to be #12 instead of #10.

Was this common back in the day? Can I extend this circuit or would that be not legal?

Thanks
 
Depends if ocp is 30 amps. If it is than it probably was commen back in the day however the egc should be #10. I believe since you're extending it u should make it right & have #10 gnd.

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Isn't there an exception if it originates from the main panel ? I think it is Section 250.140, Exception (2).
 
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Brings up another question. Why did they change it? The EGC is downsized in bigger cable, why not in #10 cable?
 
Yes, however 30a has to be sized #10. As we all know the code changes every 3 years. They used 2 have knob & tube wiring. That was changed because it was unsafe and caused electrical fires. I assume, they changed this for safety purposes as well.

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We have to go off 250.66. I have no idea what code was back when that house was wired.

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JoeNorm said:
Looked at a dryer circuit today the the customer wants extended and was pleased to find it was a four-wire. But it had an insulated EGC that appeared to be #12 instead of #10.

Was this common back in the day? Can I extend this circuit or would that be not legal?

Thanks
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I think it might be "legal" to extend the circuit as long as your extension used #10 egc.
 
I've had two houses with NM cable with the EGC being 1 size smaller than the other conductors in #14, #12, and #10 cables. Some of this was the cloth covered stuff, others were plastic sheath. The plastic sheathed one also had the EGC green insulated instead of bare. Those little 16 gauge EGCs are easy to break off in #14 NM cable, especially if they are run out the back of the box, twisted together, and wrapped around a box screw.

I would think it would be legal to extend that circuit as long as the extension complies with current code.
 
Thanks all. I am going to go ahead and extend the circuit. Of course I will use #10 for the new portion of EGC
 
Don't forget any NM dating that far back was only using 60deg wire, and any application that might have allowed heating of the cable (including encapsulating in insulation as in an attic space, most times related to lighting) historically have damaged insulation on the conductors (burnt, brittle, or even missing). May need to go back a distance to get clean splicing location as a result. Have had a lot that even checking several tens of feet still show brittleness and can hear cracking of insulation as cable is flexed, ended up just replacing whole line with new. If estimating the job I would simply include the cost of complete rewire of such circuits.

readydave8 said:
I think someone wanted to sell more copper
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I think the rationale of equivalent EGC to ungrounded conductor sizing is the need for the EGC to carry the full fault current of a given conductor set, not as relationship to some copper consortium. If the EGC was too much smaller than the ungrounded conductor (like found with 12/2 that had a #18 or #20 EGC), it would fail before opening the circuit protection if a fault was to occur. If they even hooked up the EGC at all.

Seen too many that some installer just cut off the ground or slightly better had coiled back on itself the EGC and whatever continuity the cable clamping device provided was all you get. Most times on metal boxes, but I've seen the second done on a plastic box, not sure who thought that would do anything.
 
mtnelect said:
Isn't there an exception if it originates from the main panel ? I think it is Section 250.140, Exception (2).
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That is for when using the grounded conductor for bonding the frame of the appliance, which OP said he does have 4 wire cable so that isn't a factor on his application.
 
don_resqcapt19 said:
I think prior to the late 60s the EGC in NM was smaller than what is currently required.
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Question is when and why did they increase size of EGC needed for 30 amp and less OCPD, since those are the ones that require same size as what the ungrounded conductors typically will be. Above 30 amps the EGC is and has been for a long time allowed to be smaller than what the ungrounded conductors typically will be.

Kind of guessing it maybe had a little to do with impedance of said conductor and what impact it may have in reducing the amount of fault current, though it is difficult to make a one size fits all situations as the reduced sizes likely are sufficient in some situations
 
kwired said:
Question is when and why did they increase size of EGC needed for 30 amp and less OCPD, since those are the ones that require same size as what the ungrounded conductors typically will be. Above 30 amps the EGC is and has been for a long time allowed to be smaller than what the ungrounded conductors typically will be.

Kind of guessing it maybe had a little to do with impedance of said conductor and what impact it may have in reducing the amount of fault current, though it is difficult to make a one size fits all situations as the reduced sizes likely are sufficient in some situations
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No idea of why, but the 1968 code was the first one to use the full size EGCs for 30 amps and less. The 65 code permitted a 16 AWG EGC for a 20 amp circuit where the EGC was part of a cable assembly. It also permitted a 14 AWG for a 30 amp OCPD, and 12 for a 40 amp OCPD.
 
I never liked nonmetallic-sheathed cable, always tried to use armored or flex in residential. City Los Angeles used to have the strictest building codes until the federal government stepped in with Romex to reduce the cost of new buildings. Like aluminum wire to replace copper, that was a winner. I have done work in the City of Glendale where they used electrical metallic tubing in the walls.
 
mtnelect said:
I never liked nonmetallic-sheathed cable, always tried to use armored or flex in residential. City Los Angeles used to have the strictest building codes until the federal government stepped in with Romex to reduce the cost of new buildings. Like aluminum wire to replace copper, that was a winner. I have done work in the City of Glendale where they used electrical metallic tubing in the walls.
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The strictest codes would be Chicago & it's suburbs with their residential EMT requirements, like it or not, NM cable "Romex®" has a pretty decent safety record, even a material I don't like SE cable, has a good record.
 
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