2 prong to 3 prong with old NM cable

BostonMike

Member
Location
Massachusetts
Purchased a house built in 1960. Still going through the electrical, but discovered it to be mostly updated with some old cloth NM cable still used on a few circuits, mostly in the bedrooms. 2 prong receptacles are still in use, but they are old and I'd like to update them.

Easiest thing to do for short term is new 2-prong receptacles. Long term, i'd like to replace them with 3-prong receptacles.


I've been trying to explore routes to run new cable, but discovered the NM cable they are using is the reduced ground variety. In some locations, someone has pulled the EGC into the box and wired it up as you would expect it to be today.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
What is your question. Are you asking if you can use the reduced ground as an equipment grounding conductor with a grounded receptacle? IMO, yes if it is existing.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
you are dealing with a 50+ YO house.

you will probably be well served by gutting the electrical, HVAC, and plumbing systems and starting over.

You probably do not want to hear that but if you don't do it now you will be doing it on a piecemeal basis on an ongoing basis. Better to just take the pain now.
 

BostonMike

Member
Location
Massachusetts
What is your question. Are you asking if you can use the reduced ground as an equipment grounding conductor with a grounded receptacle? IMO, yes if it is existing.

I posted in the middle of typing my question, but you hit upon exactly what I was eventually going to ask.




More info that should have been included in original post.

Home dates to 1960, but has been relatively updated. Electrically speaking, there remains maybe 4-5 circuits of older cloth wrapped NM cable with a reduced ground. Everything else is newer romex, a newer panel, generator hookup and modern fixtures. The old style cable feeds some of the bedroom and hallway receptacles which are 2-prong variety. The receptacles are aged and painted over and need to be replaced. I'd eventually run new circuits, but short term was going to install new 2-prong receptacles.

Question here pertains to the way it was wired. The EGC was connected to these boxes by back strapping them and connecting the EGC to the outside of the box at the wire clamp. On the panel end, the EGC is connected the same way to the wire clamp. All other modern wiring in the panel is connected to the ground bus.

Given this info, and short of pulling new wires (which I'd like to do someday anyway), can a standard, non GFCI 3-prong tamper resistant receptacle be hooked up in an acceptable manner?

Should I even bother? Or just put in new 2prong receptacles and hold off until I can run new circuits in the future?
 
Last edited:

mopowr steve

Senior Member
Location
NW Ohio
Occupation
Electrical contractor
I don't see why you can't still use the existing wire. Just fix the installation properly at both ends on how they terminated the EGC.

Id like to know who taught this, drives me nuts! I often find that ground wires back wrapped to the exterior of the device boxes, soldered then terminated under the side plate screw. Makes it a real PITA to get apart and route them back inside the box.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If you decide not to connect the EGC I strongly recommend that you install GFCI protected receptacles with "NO GROUND" stickers instead of two wire receptacles.
 

peter d

Senior Member
Location
New England
There is no way I would rewire a 1960 house wired with cloth romex. I would install 2-prong receptacles and be done with it. The only modifications I might make are putting short sleeves of modern NM cable to a j-box on overhead lights, wherever feasible and possible.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
The EGC was connected to these boxes by back strapping them and connecting the EGC to the outside of the box at the wire clamp. On the panel end, the EGC is connected the same way to the wire clamp. All other modern wiring in the panel is connected to the ground bus.

. . . can a standard, non GFCI 3-prong tamper resistant receptacle be hooked up in an acceptable manner?
To offer a perspective counter to Peter D's, I submit that the wiring is still young and, without evidence of heating or other aging, will likely have a very long life ahead.

The acceptability of the reduced EGC is not directly handled by the NEC.

The fundamental issue with the reduced EGC "back-strapped" as you describe is that the NM cable clamp isn't really listed for having a reduced copper conductor bonded to it. But your local Authority Having Jurisdiction will be the ultimate call on the matter. If your area has a history of this installation technique being wide spread, your AHJ will probably have an opinion. You don't give him/her a chance to answer "It's OK." unless you ask.

The reduced EGC should be acceptable, if it is pulled into each box, bonded and jumpered to any device. Be sure to check the cubic inch calculations, as the volume requirement is different now, than it was when first wired. You may well need to change out the box for that reason alone, which will get at the existing EGC a little easier.

If your local AHJ says "It's not OK." then you know what you have to do.
 

junkhound

Senior Member
Location
Renton, WA
To offer a perspective counter to Peter D's, I submit that the wiring is still young and, without evidence of heating or other aging, will likely have a very long life ahead.
.
+1.

Own house is 45 years old, would never even consider rewiring.

Of course, did it all myself so know it is good :lol:

QO breakers, all spec grade, 6 subpanels, lotsa conduit, etc.....

Should be good for another 100 years or more. IIRC, was $1200 in materials in 1970$$, probably unaffordable for a spec house these days. I noticed that RR7 relays are $20+ nowadays, were only $2.47 then, and have over 50 in the house. Only one that failed was one outside, failed at 40+ years due to jammed armature due to moisture outside.
 

JFletcher

Senior Member
Location
Williamsburg, VA
There is a fair chance that a) the original wiring comes into a ceiling box and branches off from there, making putting a GFCI receptacle as first device very difficult and b) the original boxes arent going to be big enough to house a GFCI receptacle (I hear Leviton is making a slimmer/smaller GFCI now, roughly 25% smaller than standard; havent used one). For now, I'd replace the 2 prong receptacles with a new 2 prong (what peter d and GoldDigger mentioned)
 
+1.

Own house is 45 years old, would never even consider rewiring.

Of course, did it all myself so know it is good :lol:

QO breakers, all spec grade, 6 subpanels, lotsa conduit, etc.....

Should be good for another 100 years or more. IIRC, was $1200 in materials in 1970$$, probably unaffordable for a spec house these days. I noticed that RR7 relays are $20+ nowadays, were only $2.47 then, and have over 50 in the house. Only one that failed was one outside, failed at 40+ years due to jammed armature due to moisture outside.
Keep an eye on those QO's. We have been starting to see problems with the bus where the breakers attach. What we think is happening is the clip tension on the breaker gets weak and the clip to bus connection heats up, corrodes and fails.

Just for info, on the last one I saw, the breaker had a 1995 date code on it.
 

junkhound

Senior Member
Location
Renton, WA
breaker had a 1995 date code on it.

Most of mine are older, probably made better :)

Good information, will check for any thermal effects next time I have a panel open. What you describe would fall into the thermal runaway condition - bad connection, heats, connection worse, heats more.....
 

user 100

Senior Member
Location
texas
To offer a perspective counter to Peter D's, I submit that the wiring is still young and, without evidence of heating or other aging, will likely have a very long life ahead.
I agree here- cloth nm dating from 1960 will have tw insulation covering the individual conductors and tw has been shown to hold up pretty well throughout the years- if it isn't compromised, it's fine. Probably good for another 5 decades.:)

As for the 2 wire outlets, I also agree w/ Peter d about replacing like with like- how much stuff, even today, utilizes a 5-15 cord cap in a home?
Also see nothing wrong with using the reduced egc with 5-15 r's if you wanted to go that route.
 
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