two prong to three prong out let

tmcgelec

New member
in a 1950s built single family dwelling the branch circuit conductors have only two wires (plastic insulated) one neutral and one "hot" no ground. the outlet it supplies is a two prong device the customer wants a three prong outlet. can i bond the neutral to the ground on the new device then to the metal device box and call it a day
 

Dennis Alwon

Moderator
Staff member
No you cannot. You need to either get a GFCI recep. or you run a new feed with ground or you can run an egc outside the cable to a grounding electrode as described in 250.130(C)
 

charlie b

Moderator
Staff member
I agree with Dennis. But I am not sure he was sufficiently emphatic. So I will say,
NO, YOU CAN NOT!

Then I will add, "welcome to the forum."
 

tom baker

First Chief Moderator
Staff member
in a 1950s built single family dwelling the branch circuit conductors have only two wires (plastic insulated) one neutral and one "hot" no ground. the outlet it supplies is a two prong device the customer wants a three prong outlet. can i bond the neutral to the ground on the new device then to the metal device box and call it a day
The reason you can't do this is for the same reason we don't reground the neutral past the service or at a seperate building. The neutral is a current carrying conductor and if its regrounded, you have neutral current on all the metal parts, raceways, etc back to the service. This can cause fires, shocks and improper operation of electronic equipment.
 

Little Bill

Moderator
Staff member
The reason you can't do this is for the same reason we don't reground the neutral past the service or at a seperate building. The neutral is a current carrying conductor and if its regrounded, you have neutral current on all the metal parts, raceways, etc back to the service. This can cause fires, shocks and improper operation of electronic equipment.
Tom, Dennis, and Charlie, I agree with all of you, but how is connecting the ground and neutral on a range or dryer any more safe than doing so at a regular 120V receptacle? Is there any proposal to change this? Or are there too many homes still with old wiring that it would be a mute point?
 

charlie b

Moderator
Staff member
I suppose the difference is that the dryer stands alone on its own rubber feet, or on its not-very-conductive flooring. So the neutral current flowing back to the panel does not have a parallel path that would include the dryer's outer shell. I suppose as well that similar statements can be made about an isolated receptacle that has no ground wire in its outlet and that is in a plastic box. At what point does tying the N and G wires downstream of the main panel become a hazard? Hard to say. Best to avoid doing it if it can be avoided.

All new dryer installations have to be 4-wire, but I don't know which code cycle made that change.
 

Dennis Alwon

Moderator
Staff member
Tom, Dennis, and Charlie, I agree with all of you, but how is connecting the ground and neutral on a range or dryer any more safe than doing so at a regular 120V receptacle? Is there any proposal to change this? Or are there too many homes still with old wiring that it would be a mute point?
Never understood why they allowed ranges and dryers to be done that way but when done with 3 wires it had to originate at the service equipment.
 

Little Bill

Moderator
Staff member
Never understood why they allowed ranges and dryers to be done that way but when done with 3 wires it had to originate at the service equipment.
Dennis, doesn't 250.140 exception (3) say that the grounded conductor only had to originate at the service equipment if SE cable was used with a bare conductor? I think if the grounded conductor is insulated it doesn't have to originate at the service equipment. At least that's the way I read it.
 

Dennis Alwon

Moderator
Staff member
I must admit I used to think that also but it seems everyone tells me I am wrong... Actually I read it now and I think you are correct. I think Bob made me think different on this but I am not so sure. It also seems to make sense that an insulated wire should not have to go back to the service panel.
 

hurk27

Senior Member
Along with the lost neutral reason found in the dryer thread, a few years ago I got a call that a elderly home owner was being shocked by a freezer in her garage, my first response was to use my 3-light tester in the receptacle it was plugged into since the freezer was new, well the correct wiring lights lit so I started to do some more testing with an extension cord plugged into a known good receptacle and my wiggy, what I found was the neutral in about 4 receptacles were tied to the grounding terminal, and new NM ran back under the crawlspace to a junction box where they were connected to old cloth covered non grounded NM, the color was no longer distinguishable from hot to neutral and they had tied the neutral to the hot by mistake, so in retrospect, this could have caused a death and cost the life of this little old lady, one more reason I have a lot of respect for the code and doing things the right way.

Remember we can be held liable and even criminally liable for what we do, a good thing to keep on your mind when doing electrical work.
 
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