receptacle off knob and tube wire?

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Old 05-11-18, 02:30 PM
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receptacle off knob and tube wire?

Is it safe to connect a knob and tube wire to a GFCI receptacle, guage wise?
I have a junction box running lighting so I assume to knob and tube is 14 guage.
I want to run a receptacle but there's no ground. So, is a gfci ok? Is the old knob and tube wire good enough to carry 15A current?
Most electrician's I see replace everything except lighting circuits where they leave knob and tube in place.
 
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Old 05-11-18, 02:42 PM
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I want to run a receptacle but there's no ground.
It is an NEC code violation to extend an ungrounded circuit.
 
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Old 05-11-18, 03:00 PM
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GFCI receptacle? That's code compliant, no?
The receptacle is already there but it looks like a new 3 prong.
But can you do this with knob and tube wires?
 

Last edited by qwertyjjj; 05-11-18 at 03:23 PM.
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Old 05-11-18, 06:25 PM
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If you mean replace an existing- 2-prong receptacle with a GFCI wiring method doesn't matter but you can't add a new receptacle to the- circuit-.
 
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Old 05-11-18, 08:13 PM
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It would be helpful to listen to the code compliant advice that is given instead of looking at ways to get around the code.
 
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Old 05-12-18, 05:40 AM
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Provided that the outlet box was originally part of the knob and tube circuit and originally contained a 2 prong receptacle you may (should) remove the (erroneously placed) regular 3 prong receptacle and substitute a ground fault circuit interrupter receptacle unit.

It is possible that the GFCI receptacle does not fit in the box. It is my present opinion that the box may be replaced with a larger one and the existing (K&T) wires re-installed treating the box replacement as a repair. They make box extenders (thick rectangular gaskets also called rings) that fit around the box opening in front to give more space in back for the wires and save having to dig the orignal box out of the plaster wall.
 
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Old 05-12-18, 05:59 AM
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It looks like the junction box has a knob and tube source but the 3 prong receptacle has 3 wires (ie includes a ground) so it was extended by someone else (not sure when).
As a new owner of the building, am I not grandfathered in by this and allowed to put in a GFCI?

If I was, as a separate question, because I have some 2 prong outlets as well in the building, can knob and tube wiring handle receptacle loads of 15A?
 
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Old 05-12-18, 06:01 AM
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es, K&T can handle 15 amps.
 
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Old 05-12-18, 06:36 AM
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I am not sure how many times the NEC code has changed since 1940. If an extension from knob and tube wiring was against code at the time it was made then, if it is still in place, it would still be against code today.

A junction box or outlet box with just oriiginal K&T wiring is not grounded. Anyone who brought in an NM-B (e.g. Romex) cable to that box and screwed the bare wire to the back of the box did not know what he was doing.
 
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Old 05-12-18, 07:36 AM
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am I not grandfathered in by this and allowed to put in a GFCI
The original installation was a code violation, therefore it should be removed.

I would recommend running a new circuit.
 
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Old 05-12-18, 09:59 AM
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I'll take a slightly different viewpoint, but with the same answer.

I would never try to extend a K&T circuit. Instead, I would do everything possible to phase out any K&T circuits in your house, especially for receptacles. It's too likely for the insulation to crumble and in some cases overload the wiring. I would run a new circuit whenever possible.
 
 

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