Hi. I recently bought a small 1890 victorian in Massachusetts. It has a 100A entrance with 15A fuses (one 20A for a workbench plug in the basement). The whole house was wired with BX a few decades ago.

When I was mapping out which rooms are on which circuits, I found some live knob and tube wiring in the attic. I want to disconnect it completely (for safety) before I plan and execute a complete rewire of the house. The wires enter the attic from below (bathroom/bedroom wall) and end there with no connections. So they have to be connected to something in the wall somewhere.

The mystery is that the knob and tube wiring STAYS HOT when I remove one fuse at a time from box. That is, I remove fuse 1, check the K&T (live), replace 1 and remove 2, check the K&T (live),... The K&T is live unless I pull the mains. There are no unfused branches exiting the fuse box, and I'm sure I only have this one service entrance.

The whole upstairs including all the BX in the attic is on a single circuit. (I'm using one of those AC detector pens to find the live wires, but I haven't measured the voltage in these with a meter yet.)

Clue #1: There is a single branch going into the bathroom directly below the attic. It has one switch turning on two 25 watt wall lamps. When the upstairs/attic fuse is out, both wires in the switch light up my pen. (These wires look like BX wires at the box.) The two wall lamps stay dark.

Any idea what's going on?

re: mystery hot K---&---T in the attic	wirenuts	7:18 pm wednesday september 5, 2001

Hi Alex! I use a volt-tic daily, it's like an extention of my arm. The thing about induction testers is that they tend to pick up from other live circuits that are proximal to the one being tested. This is especially true if other circiuts have a heavy load on them, or run parrallel over a distance.

What i am leading up to is, you may have to facilitate a live test using 120V equipment. One idea would be to gently strip a 1/2" off both K&T wires in your attic ( main off of course) then get a pigtail ( rubber lampholder w/ two wires) and make it onto these exposed points. You could even srcew in one of those receptacle ditty's and plug a radio in ( i work alone so i do stuff like this...) but if you don't mind pounding stairs for every fuse your a better man than i.....

Next, you need to determine what this circuit actually activates, as this is an original circuit ( BX came latter) it may be quite extensive ( wired back in the ol' one circuit does all days..)

Once you have carefully determined this out, you can even map out a point to point progression of the circuit. This will help in your replacement of it.

There may be some area's of this circuit where the level of destruction to replace it becomes more of an expense that anything else. For this , i can only foward 2 options....

#1---run some surface raceway such as wiremould

#2---cut the existing K&T back to minimal duty, reterminate everything possible, box any unboxed junctions in plastic old work boxes ( can be steel, but plastic makes more 'lectrical sense with no grounding conductor) and install an arc-fault circuit breaker on it.

p.s--please be careful with some of my offbeat suggestions here, i do this for a living and tend to be a tad cavelier...:)

re: mystery hot K----&----T in the attic	JuiceHead	8:46 am friday september 7, 2001

I also have an old home with some K&T circuits remaining. It's an 1877 cape in upstate NY. I entered into the deal having a digital multi-meter (DMM) without which I feel my ability to determine what the heck was going on would have been crippled. The non-contact type meter is great for certain things, but as Wirenuts indicated they can also mislead you on some everyday diagnostic attempts. I would recommend you get a multi-meter, although not necessarily digital if you feel you won't use it enough to make it worth your while. Home Depot sells a Sperry analogue multi meter (It has a sweep scale with a needle). It's a model SP-5A and sells for $9.94. There is another model which is digital that goes for $29.93, model "Pocket Pro" #DMZA. Radio Shack sells a nifty little digital for about $25 that has a case which stores the meter and the built-in probes, and is very accurate.

Anyway, in order to truly determine which way is up in your electrical system I would test the bare wire ends with a proper meter. I would remove all the fuses and test those wires you described. Once determined to be truly dead I would screw in one at a time, unscrewing it again if that fuse isn't the one and you move on to the next. I would not have more than one fuse screwed in at a time during diagnosis after reading the confusing results you previously described.

Personally I would go ahead and rip walls open, but then again I have a lot of experience with drywall installation & repair so I'm fearless of destroying my house to do investigative surgery. Plus the previous owner screwed up the walls and many of them need to be repaired anyway.

Wirenuts is right about locating any junctions or taps and putting them in a non-metallic device box. This is Code anyway. Furthermore all boxes must be accessible with the walls closed up, even if it's just a blank wallplate. When the K&T was installed this was not a requirement, and if the circuit is not modified at all it is grandfathered and is legal if installed that way when the practice was legal. But from what you tell us, the previous owners have done modifications all over the house (BX).

What I have done was to replace whole circuits one by one as I got the time and money. I added individual circuits to individual rooms or areas as logic dictates, instead of "one circuit serves all" as it was originally wired. Having a 4-fuse box and a 2-fuse sub-panel the previous owner installed I doubled- up or even tripled-up the wires on the fusebox's terminal screws. I realize this is improper, and can even be dangerous if not fully and securely held by the screw, and properly tightened. I was careful. But I was leading up to eventually replacing the panel. This I did last year, the fifth year in this house. I bought a 30 space/150 amp panel, pulled a permit (Homeowners are allowed to do their own electrical work if a permit and inspection are obtained) and had tons of space to run a single circuit off each breaker.

You mentioned 15 amp and 20 amp fuses. I would like you to know that 20 amp fuses can only be used if the entire circuit they feed is wired with #12 AWG. If there is #14 or K&T wire on a 20 amp circuit you must reduce the fuse size to 15 amps. K&T is nearly always #14, which is rated max 15 amps and will overheat if you try to pull 20 amps through it. This causes many house fires annually. The idiots that owned my house before me filled the box with 30 amp fuses, probably because of the nuisance of running to the basement every other day and changing blown 15s and 20s. My definition of a real nuisance is REPLACING EVERYTHING YOU OWN WHEN YOUR HOUSE CATCHES ON FIRE!!! First thing I did was to replace all the fuses with 15 amp ones and throw the 30 amp fuses directly into the trash so nobody would possibley use them in a pinch.

Well, I think I've rambled on long enough. Hope I've been helpful, and I hope you find out what's going on and are able to proceed with your plan to eliminate that attic K&T. Be safe out there!

Juice

re: mystery hot K-----&-----T in the attic	Alex	10:30 am tuesday september 18, 2001

Thank you wirenuts and juicehead for your suggestions.

I tested the knob and tube with a meter as you both suggested, and I have found that the potential between the hot and "neutral" knob and tube wires never gets very high. It seems to be some kind of induced current or a ground fault. If this attic wire is connected to ground somewhere below that would be pretty scary -- and I'm fortunate to have discovered it. I'm not sure that the "neutral" wire is well-grounded, and there's no good ground in the attic that I can trust (even if I open another cable somewhere because they're all 2-wire with no ground).

Since my post, I have discovered additional branches of knob and tube (e.g. under the hall lamps, with hickeys from 1907). I've also discovered that the original BX job included such deprecated practices as splicing outside of boxes. I found one place where the feed for a light fixture was spliced (below the hickey with the lamp itself) to two additional rooms! No box of course.

I've decided that a complete rewire is in order, and I'm now trying to decide whether to go with temporary power and do the whole thing at once or to replace once circuit at a time (as you did JuiceHead) and put in a new panel when I'm done.

What an adventure this has become!

Thanks guys.