# Knob & tube how do i get it grounded



## erikthered (Nov 3, 2005)

I'm doing work on a old farm house. I know you can put a junction box in and feed off of it. but there is no ground the knob & tube is in great shape. but i don't want to be up every night "Worring Every Night"


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## mdshunk (Mar 13, 2005)

There was a time when ungrounded extensions of to Knob and Tube were popular. These extensions were accomplished in one of two ways:

1) The extension was done with NM cable. The NM cable started at the K&T by coming out of a "monkeyface connector". This looked like a regular romex connector, with a plastic bushing screwed on in place of the locknut that has a individual hole for each conductor. You left enough black and white stick out of each hole to tap onto the K&T with open, insulated splices. The extension was just run with romex from there as you would normally.

2) Each conductor of the K&T was sleeved for a foot or so with fiber loom and the hot and neutral of the K&T were each brought through a seperate knockout in a 4x4 box via a "federal bushing". This is a porcelain bushing with a locknut. Inside the box, NM cable was tapped onto the K&T and run traditionally from there.

You won't find "monkeyface connectors", fiber loom, or "federal bushings" on the market anymore. They may still sell them at the same store where you buy spark plugs for a DeSoto, right next to the cans of lead paint and asbestos furnace cement.

The code does permit extensions from K&T under certain criteria. I would advise against it. Th K&T has already served it lifespan, as the insulation has been sufficiently stressed throughout the years. Adding additional load to a vintage K&T system is unwise. While you can wire in accordance with the 250.86 provisions, I would very much advise you wire to the normal 250.130 which requires an effective equipment grounding path.



> 250.86
> Exception No. 1: Metal enclosures and raceways for conductors added to existing installations of open wire, knob and tube wiring, and nonmetallic-sheathed cable shall not be required to be grounded where these enclosures or wiring methods comply with (1) through (4) as follows:
> (1) Do not provide an equipment ground
> (2) Are in runs of less than 7.5 m (25 ft)
> ...


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## datafan (Aug 27, 2005)

I have rewired/upgraded a couple houses that had the old knob and tube, it is a big job and depending on the house can require things like tearing up flooring on upper levels, and for sure a lot of time fishing wires and cutting boxes into lath and plaster. All the existing boxes will be too small, and you will swear they are nailed to the studs with pole barn spikes, as you try to remove them from their lath and plaster encasement you will have chuncks of walls and ceilings falling down all around you. It seems the old knob and tube houses I have seen there are usually 2-3 circuits feeding the entire house if your lucky. Even if it's in good shape as you say, it just wasn't designed to accomodate todays normal electrical loads. Also check the attic and see if that old knob and tube wiring is buried in insulation, so you have an ancient, over-amped heat producing wire buried in dry dusty paper insulation...  Sorry to be so doom and gloomy, just going off my personal experiences with it.


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