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Discussion Starter · #1 ·
So we just moved in - and spent some time in the attic. This house is 1943, and is knob n tube wiring. It's all in good shape, and I will not be rewiring soon. At some point, I would guess in the last 5 years, the previous owners had a heater/blower unit installed in the attic. The installers spliced into the knob and tube, I believe, and finished the circuit with romex. See the picture - is this "fine". should it be in a box? It looks a little fishy to me, so I thought I'd ask you all for your thoughts.

Thanks,
658661
 

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that looks like a doorbell transformer.


my basement had updated wiring, but the main house, no. i replaced it all.
 

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There is no good way to tap into K and T, but that is the way the whole system is done. Surprised a house from the 1940's was in K and T. I once saw a house built in 1925 that was wired in NM.
 

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It is against code to extend an ungrounded circuit. I have never seen a K&T circuit that was grounded. So adding the NM cable for the heater/blower is not code compliant.
 

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Discussion Starter · #9 ·
I only took 1 other photo for something else - so it's not a great pic - and I don't want to go back up there for a pic. But you can see the tubes running through the ceiling joists in this pick. Pretty much the same across the rest of the attic.
658688
 

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Discussion Starter · #10 ·
That first pic above, is the only NM in the attic. goes from that "splice" to an electrical outlet, which the blower/heater is plugged into.
 

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The black single wires could either be "bell wire" (typically 18 to 22 gauge) or knob and tube wire (14 gauge) but are okay because they are connected to the low voltage terminals of the transformer.

The line voltage (120 volt) primary wires are on the other side of the transformer, do not have exposed screw terminals, and look to be correctly wired into an outlet box with Romex coming out and going to the panel.

Usually a doorbell or air conditioning low voltage transformer is mounted on the outside of a box and the primary wires go through a clamp or nipple directly into the box and are not visible from the outside.

Nothing wrong with repurposing K&T for low voltage except it could look confusing to the next person to service or analyze the wiring.
 

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Is that what that is? A transformer?
Yes it is a transformer but it does not appear to be the original one. The one that was installed before was meant to have it's primary wires run through the 2 holes in that box cover. Those wires would have been insulated with rubber covered with woven cloth. The one there now was meant to be installed through a knockout on the box rather than the cover so that the primary wires are entirely inside the box. It's not supposed to be laying loose like that. Remount that transformer through a knockout on the box. There will be a flange that goes through the knockout and a screw that tightens against the other edge of the knockout from the inside of the box to hold the transformer to the box. Splice the transformers primary wires to the wires in the box just as they are spliced now. Replace the antique box cover with a flat one of the correct size. Do not install the transformer through a knockout in the cover.

It is important that knob and tube wiring not be surrounded by insulation. The natural rubber insulation that was used on those wires will get too hot and turn into dust leaving the wires uninsulated thus exposing any living thing that touches it to a shock and any conductive thing that touches it to becoming energized so that anyone who touches it will get a shock.
If there is now insulation around the knob and tube wires there is a danger of shock and fire. Since your not going to remove the insulation you are going to have to rewire all of the K&T wiring that is now buried in insulation.

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Tom Horne
 

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Discussion Starter · #15 ·
hornetd, can you give me an example of the box you're referring to? I assume it's not the panel, but an enclosed metal junction box? want to make sure I'm understanding.
J
 

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hornetd, can you give me an example of the box you're referring to? I assume it's not the panel, but an enclosed metal junction box? want to make sure I'm understanding.
J
jousley

I mean the box that is already there.
Helmet Grey Rim Font Automotive lighting
That box has 2 cables going through it. You would twist out one of the knockout blanks that covers one of the 2 unused knockouts, mount the transformer on that knockout,
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I cannot see the side of the transformer that it's primary (120 volt) wires come out of. It will have some means of attaching that transformer to the box. if you give me a photograph of that side of the transformer I will tell you how to install it through the knockout into the box.

You replace the existing cover, which has the 2 bushed holes for the primary wires, with a plain blank cover which does not have a knockout in it.
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That puts all of the 120 volt wiring in the box and leaves only the low voltage secondary wires exposed.

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Tom Horne
 

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Discussion Starter · #17 ·
Actually. There is no box. Kimda the reason i was posting…. It looked questionable.
 

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Actually. There is no box. Kimda the reason i was posting…. It looked questionable.
OK. Here I thought that a box was buried in the insulation beneath that cover. If you can find a place were both cables will still reach the box install a face bracket box like this one.
Toy Rectangle Automotive exterior Wood Box

It will be easier to install because you can nail or screw into the top of the floor joist instead of the side. Proceed as in my previous post but use a 4 inch square cover.
Rectangle Gas Automotive exterior Fashion accessory Metal
You will need 2 two non metallic sheathed cable clamps.
Body jewelry Goggles Jewellery Silver Personal protective equipment
Alternatively you could buy a box with the clamps already fitted.
Rectangle Gas Auto part Font Fashion accessory

Again just install the transformer through any available knockout on the side of the box. The center knockout opposite the mounting flange will be the easiest to use. Do not forget to install a Equipment Grounding Conductor (EGC) pigtail and splice it into the bare EGCs from the 2 cables and the bonding jumper from the transformer.
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The 10/32 tapped hole for the screw is right next to the center knockout in the bottom of the box. Staple or strap the cable to the side of the joist within 1 wire foot of were it enters the box. The cable should be at least 1&1/4 inches from the top of the joist
Sleeve Font Rectangle Parallel Electric blue
Immediately after the cable staple
Rectangle Automotive exterior Parallel Auto part Font
or strap
Household hardware Tool Composite material Nickel Bicycle part
bend the cable out away from the joist to enter the box at one of the box's cable clamp knockouts. Since those knockouts are closer than 1 1/4 from the top of the joist don't keep the cable close to the joist as it bends up toward the knockout. If you use a 2 1/8 deep box instead of the 1 1/2 inch deep box then you will not have to be as fastidious because the knockouts will be further away from the top of the joist than the 1 1/4 inches which the US National Electric Code requires.

If you have any questions please ask!

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Tom Horne
 
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