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I am in the process of planning to upgrade my house's wiring. My house was built in the 1920s. It most likely uses tube and knob wiring. I am not sure as I have not looked in the walls yet. It does use it in the attic. The house currently uses a 100 amp service. The house is 2000 square feet. I am planning to add a 2nd building to the property that would be equal to a 1 bedroom house. I will have each room be on its own breaker. All the work will be done by an licensed electrician.

Here are the steps I am planning to take.

  1. Using a stud finder, I go around marking the paths the electrical wires take through the ceilings and walls.
  2. Map all the outlets and fixtures in the house to specific breakers.
  3. Upgrade the service to 300 amps from 100 amps. This will also replace the current main breaker. I will also add an external main shut off panel near the main meter.
  4. Have the first floor and basement rewired.
  5. Have a subpanel installed on 2nd floor and upgrade wiring on 2nd floor and attic.
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    300 amps is a very large service for residential, and may not be possible from your electric provider, depending on their capacity. There also typically isn't a need to have each room on its own breaker. It is recommended to have lighting and outlets on separate outlets, but having each room its own breaker is quite unusual. If you're going to have a licensed electrician do the work, then have them consult on what you're wanting to do. There's a good chance you're either over-thinking, or forgetting necessary things on your plan.
    – Milwrdfan
    Commented Jul 12, 2023 at 17:59
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    On a standalone structure that doesn't have at least a connecting breezeway, you can't run a bunch of circuits over, you must run 1 feeder and then have a subpanel. "1 circuit per bedroom" is not a good design guide, Code doesn't care and it wastes wire circling rooms. I advise something more akin to "1 circuit per wall" which allows any given room access to 2-3 circuits, rather handy if you ever set up a home office! Commented Jul 12, 2023 at 18:55
  • You may be getting confused about breaker/circuit sizes and the total service. A typical house could easily have breakers that add up to a lot more than the service size. For example, mine add up to 515A, divided by 2 (because service size is based on 240, not 120) = 257.5A. I have a typical 200A service, but prior to the panel replacement I had 100A service and never came close to exceeding that and have not added any significant new circuits since then. Since you are OK currently at 100A, an upgrade to 200A will likely give you plenty of headroom for the second building. Commented Jul 12, 2023 at 19:42
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    If your utility is like mine, you will go from 100A to the current local standard (likely 200A, but could be 225A) automatically as part of the panel replacement process - and you will need a new panel because you will be adding lots of new circuits as you replace the old circuits. But the key is a Load Calculation - put in your current circuits, anticipated new circuits, square footage, fixed appliances (HVAC, cooking, dryer, etc.) and that will tell you how much service you actually need. Commented Jul 12, 2023 at 19:44
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    All the work will be done by an licensed electrician. - then what's the question? 1) remove all wall sheathing. 2) plans drawn for all outlet locations. 3) will be decided by the (non?) availability of 300a panels. 4) and 5) are covered under "gutting". - "Is this a sound plan for rewiring a 1920s house?" as long as it begins and ends with, "I am gutting the house."
    – Mazura
    Commented Jul 13, 2023 at 13:22

2 Answers 2

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  1. How will a stud finder find the wires? Usually, there is no bonafide way to identify a buried wire's run except by trial and error. This is why after virtually every knob-and-tube removal, there are huge patches of wall removed all around the house that need to be plastered, repainted or what have you. If you want to save money, you can get your own oscillating saw and cut out the sections for the electrician so all they have to do is pull wire - otherwise the electrician does the same and still charges you for the time. Lucky owners who had wire run after initial construction have wires that aren't held by staples and can tie a fishtape to the wire and just yank the wire through the wall a considerable distance.

  2. You can do this part by switching the breakers rather than chasing the wire back to the source, hopefully your panel is actually labeled correctly so this isn't technically necessary. You (or electrician) can just transfer breakers and labels to the new panel. If they're wrong for any reason, it's never too soon to correct the labels as needed.

  3. 300 amps is too much - what kind of appliances are you running? And is the second property going to be metered or are you running a subpanel to that property (like a MIL)? Even if both have a electric dryer and range, you can have 100 amp subpanel in the second building and 200 amp main in the main building.

  4. Yes, do the needful.

  5. This seems totally unnecessary. Even if you run a subpanel upstairs, you will have to fish like a 3 ought wire two floors up for just like 20amps tops. Since you're already cutting a dozen holes that will need plaster and paint, why not cut a dozen more to run to the top floor? You still need to get rid of your top floor knob and tube anyway.

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  • You can find wires by disconnecting them from the panel then running a signal generator through them to use them as antennas, or by dumping an above-spec current through them briefly to heat them up and using thermal imaging to see where the walls heat up. Commented Jul 13, 2023 at 21:17
  • If knob and tube wiring is disconnected from mains, what additional benefit would there be to removing it? I would think that if one disconnects everything from the utility entrance and connects a signal generator to what used to be the mains input, a signal tracer should pick up any knob and tube wiring that's still connected much more strongly than any newer wiring where hots and neutrals aren't inches apart.
    – supercat
    Commented Jul 13, 2023 at 22:45
  • @supercat For one, many insurance policies demand there be no K&T wiring. You could lie, but it might be a helluva headache if you have to file a claim down the road. Also, it would be an unpleasant surprise to go hacking through the wall and finding wire you weren't expecting not knowing if it's live. The next guy is you!
    – AdamO
    Commented Jul 13, 2023 at 23:12
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I just did my own house and...

  • your knob and tube are kinked in insulators inside your walls and are run separate through the home
  • you have lathe behind your plaster. you are in for a real treat
  • you need to replace your drop service (from the main power line),weatherhead, meter socket, panel, and ground everything first
  • you will trace nothing with any non contact tester, you will be cutting holes or gutting it
  • check if you have galvanized pipes. You want to replace those trust me. They are FULL of rust on the inside. That will give you some openings to run wire upstairs. Then wire the 2nd floor from the attic. Outside walls are going to be tough but your house is balloon framed so you basically have a chimney between each stud that goes from the basement to your attic. Should put some fire blocking in there. Look it up, it will save your life.
  • your breakers are not on rooms. you will have west wall living room, north wall kitchen and dining room light. The wires will be soldered together in places, you will see in the attic floor.
  • You cant combine new and old wire first of all. Doing the downstairs you will loose power to upstairs the way the wire was ran back then. Your hallway light on the steps will not work because it's a 3 way and you have one 3-way up and one downstairs.
  • You have no grounds if you have knob and tube as well as metal boxes (crazy right) The number one thing to be weary of is you can not lose a neutral or your house will most likely burn down. Your insurance wont even cover knob & tube as in they will not insure your home at all unless your removing it.
  • adding shut off panel near the main meter...that becomes your main disconnect and everything after is a sub
  • You need to call a licensed contractor and don't worry about your stud finder gadget and messing with any wires. Your panel switching plan needs to be revamped because if your grounds. It makes more sense to drop your SE cable to a main service panel in basement for multiple reasons. You have to have floating grounds to your subs, the wire to run to a sub upstairs...idk my friend. Your 300 amp is not going to happen, what the heck are you running a machine shop? (joking) I want you to be safe. They will do all of that for you, cut the smallest holes so the plaster keys don't break and pop off the wood lathe. It is a big job and your safety and family or friends safety is important. If you do have romex from the 60's it can have asbestos in it, there is tile with asbestos and pipes that may be wrapped in it. I wish you the best of luck and you will see what I am talking about.

p.s. Check your bathroom stack. Now would be the time to get that cast out of there. It probably runs down your staircase wall from the second floor to the basement. It's not if but when that begins to leak because its rusted you will have a mess in those walls. If it is pvc you are blessed. Love my old home (1913) with the oak trim and doors. These houses lived over 100 yrs and after upgrading and insulating, a 100 more.

Have fun and stay safe!

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