Locating Knob and tube wiring

[dmcintosh]

So this is not exactly garage related, but I would like to mine the collective wisdom you all have. I have a couple of circuits in my house (built about 1890) that the previous owners never upgraded from the knob and tube style wiring. Long story short is that I am working on another project (bathroom addition) and it seems prudent to replace these wiring runs before the walls get closed in, etc. Anyone have suggestions on how to trace/locate the path of these wires? I know what they feed, but am trying to minimize collateral damage to the walls and ceilings in where they run from the accessible end to where they terminate. In this case, one circuit feeds the upstairs light, and one feed the lights downstairs.

 

[TRWham]

Can you simply abandon the K&T and route new cables wherever is convenient? We are renovating a house built in 1890 that had its K&T replaced long ago. Some visible bits were left and the inspector has asked us to remove those, but anything hidden is not an issue.

 

[dmcintosh]

That is my plan, but I am not quite sure how/where the old wires are running. I was hoping to access the specific fixtures as much as possible from the floors above, but am trying to cut a bunch of holes in the walls and ceilings to locate splices, etc. I THINK I can access most of the 2nd story from the attic and rewire to pick up all of the fixtures on that circuit. the downstair is really the bigger issue with the finished space above. Hoping that if I can find the original pathway I can use that general course to strategically cut access holes and run the new wire. thinking of purchasing a camera to try and see inside the walls/ceilings, maybe something like this one from Amazon.

 

[AntonLargiader]

It's often in a loop. so you have hot in one place and neutral in another. Not always conducive to simple same-path replacement with NM especially when you have switches and lights.

I would just look at it and figure out the best way to run new wiring, and remove whatever K&T you encounter. I used to think like you are thinking, but that was before I actually did it...

 

[Stuart in MN]

It's often in a loop. so you have hot in one place and neutral in another. Not always conducive to simple same-path replacement with NM especially when you have switches and lights.

Exactly. Trying to trace knob and tube wiring in a logical manner can lead to tears.

 

[bwringer]

Yep, remove what you can reach easily and "abandon in place".

 

[Bert_]

I'd just replace what I can get to with reasonable effort and leave the rest until the next remodel project uncovers it.

It's really not a safety issue if it hasn't been hacked and there aren't major electrical loads on it.

 

[stonesg]

I did a two story house by accessing the lower floor from the basement/crawl and the upper from the attic.

It ended up being simpler to put a sub panel upstairs and run the those circuits from there.

All the old stuff was just abandoned in place as has been mentioned. I pulled out what I could reach without to much destruction (plaster/lathe) and left the rest.

 

[Hot Rod Grampa]

My question would be where is the circuit fed from. Are you working on the tail end of the knob and tube so you can cap off what you can reach and re wire to new code or are you at the beginning of the circuit or are you cutting into the middle of it? Each situation may require a different approach. The early systems brought power to the center of the ceiling, switch wires to the door. Outlets were added later. Maybe you could find where the k&t went from the service entrance. Otherwise the borescope camera will be your friend. I have a Ryobi one, drill a 3/8 hole and you can see what you have up there.

 

[sberry]

I do it all new. It's part of a real remodel. Forget where the original is run.

 

[TRWham]

If you really want to try to find the old wires, you could try a dual range non-contact tester. It has a lower range for low-voltage AC that might be more sensitive when sniffing through walls. I have one and once experimented a bit doing this. It worked where I tried it, but cannot claim to have tested the concept scientifically.

 

[DenisG]

They make electronic circuit tracers for tracing electrical wires in walls (Ideal SureTrace), but they are expensive:
https://www.amazon.com/dp/B00DEDM06M/?tag=atomicindus08-20
You might be able to rent one from a tool rental place.

 

[sberry]

A couple more things. All brandy new is good, 2nd. Modern codes especially kitchen and bath have changed, this is the perfect time to run new circuits and all was on the old doesn't need to stay on it, new wire right back to the panel is the best. I even replace olde romex, even 60's stuff.
If you keep the house you want it new and if I was selling it would tout new wire. Insurance loves you when you do this. Old circuits like that are original. They often have a lot of stuff cobbled on, jboxes not seen in the attic are suspect. I found some had near bare wire laying on steel pipe to the bathtub a while back in one. A dozen faulty splices. A recent house I looked at has some upgrades and an added panel. Had 12 circuits, the original 2 had kitchen, fridge, bathroom and laundry and most of the lights. Most of the added ones didn't carry any of the load. . Did a remod recently,,, was 1 15, kitchen bath and fridge, replaced it with 5. 2 kitchens, a bath, a micro and fridge.
Replace any to adjacent rooms while that wall is down.

 

[Two Sheds]

Some studfinders have a mode in which they are able to detect wires within the walls.

When I replaced my K&T, I had access from the attic and basement, and started by disconnecting all of it, and removed everything that was visible, and then fished new cable.

But, if you are just replacing part of it, you will need to locate it. It can certainly run off in unexpected directions, with splices anywhere along the run.

 

[Bert_]

I'm a little confused, how many walls do you have open? I thought it was just a section of wall or two. The way sberry talks makes it sound like you have many walls open. Did I miss something?

 

[dmcintosh]

Thanks for all of the thoughts and comments. Situation is this. I added a second story addition - did not change the overall footprint, just added a room above the mud room for a second bathroom. So, this means that much of the mud room walls are open (to varying degrees),and this is where the electric panel is. And, what was the exterior wall on the second story, now the inside wall of the bathroom addition is just bare studs. The previous owners had upgraded the bulk of the electric probably back in the late 1980s. I upgraded the service panel when I added power to my shed a few years back. So, for the most part, things are ‘modern’ with the exception of two circuits. As far as I know, I would tapping in at the supply end of each, and trying to trace/replace wires from one end of the house to the other.

 

[finn]

A thermal imaging camera may work. You can buy an inexpensive attachment for your iPhone or Android. The two brands I am familiar with are Flir and Seek.

I have the Seek, but recommend the slightly more expensive Flir.

Load up the circuits and you will be able to see the outline of the wires on your phone screen.

Having said that, it’s only a “nice to know”

Abandon in place and run new circuits to modern code.

 

[Bretny]

That is my plan, but I am not quite sure how/where the old wires are running. I was hoping to access the specific fixtures as much as possible from the floors above, but am trying to cut a bunch of holes in the walls and ceilings to locate splices, etc. I THINK I can access most of the 2nd story from the attic and rewire to pick up all of the fixtures on that circuit. the downstair is really the bigger issue with the finished space above. Hoping that if I can find the original pathway I can use that general course to strategically cut access holes and run the new wire. thinking of purchasing a camera to try and see inside the walls/ceilings, maybe something like this one from Amazon.

Just run all new wire. I would do one or two home runs to the pannel. One for lights/fan and one for outlets. Hair dryers or a small electric heater can really draw.

 

[Bert_]

I think we all agree the new bathroom and the utility room with open walls will get new wire/circuits.

For the rest of the house that does not have walls open I stand by my earlier statement.

If you truly want to do a complete rewire then you should gut the whole house. You can do a better job with the electrical and you can address other issues like plumbing, HVAC and insulation that you can't get to without opening up the walls.

When I do a rewire that does not involve gutting a house I usually do the following things. Redo the downstairs outlets, because they are pretty easy to get to from the basement. Bathroom, because hairdryers/ect. Kitchen outlets also because of possibility of large loads.

I very rarely redo wiring to lights. These are small loads that have not likely been tampered with over the years so the risk is very low in my opinion.

Depending on whether the customer is ok with the number of outlets in upstairs bedrooms and if there is an attic with room to get into, I may or may not run new stuff up there.

 

[sberry]

There is a tipping point for me which include several things, the age of the wire, ground or not, existing workmanship and connections etc.
I got a discount on a renewal and insurance which is somewhat unusual, I wasn't shy in a tour about pointing out service upgrade sticker, obvious it had new wire and a new p

 

[dmcintosh]

So i figured you guys deserved an update. I made decent progress this past weekend. Managed to get most of the downstairs light circuit redone (new wire from the panel to the 1/2 bath light and switch, dining room light and with, and hall light and 3-way switches). As I started to trace wires, i was actually able to find the floor boards that were removed to install the wires when the house was originally electrified. This weekend, I am going to tackle the upstairs light circuit. Hoping for similar luck - except I will need to work in the attic, and will be adding a 2nd circuit to feed the main bathroom upstairs.

As I sit here writing, I realize I didn't take any pictures of the endeavors. I'll try to fix that moving forward. And, for what its worth, I did purchase the $40 amazon camera and it was helpful in a few situations. helps with seeing what was under the floor and inside the walls where I couldn't fit my fat head. In retrospect it was probably not an essential tool for this project, but is was worth the money spent. And hey - who doesn't like an excuse to buy a new tool, right?