I’ve got a weird electrical problem and I’m hoping some of you can give me some ideas. By way of background, I’m an ex-general contractor and have done lots of wiring.
My son’s house is about 80 years old and I’m helping him do a major remodel. The older portion of the house has (well, had, until I removed it …) a fuse box with 5 fuses. The fuse box was fed by dual 12 amp wires, providing power to fuses from 15 tro 30 amps. The wiring was knob and tube.
I wanted to provide better protection here, so removed the fuse box and inserted a new Square D circuit panel. I marked all of the black wires with colored tape so that I could put the circuits back with corresponding descriptions. I hooked up the power, and ran the wires for two circuits to the breakers and the neutral bar. When I threw the breakers which powered the panel there was a large spark, but no thrown breakers. The downstairs lighting came on, but the fixture in the stairway where I was working wouldn’t work. Don’t know if it’s connected. This is problem #1.
The second problem was a real surprise. As I inserted some new breakers I got a shock. I took out my meter and one of the wires coming into the box (one that I’d disconnected) was hot. It looks like a white wire, but I didn’t mark all of them.
I need to trouble shoot both problems and am not quite sure what is the best way to go about it. For the first problem (the light not working), I’m thinking of removing the fixture and looking at the wire in the box, and doing rudimentary tests to see what is up. It could be that the fixture is simply faulty.
But any ideas as to why I got the large spark when I turned the power on, and what could be causing the live wire that should be dead? On the latter item, I’m thinking there must be a back feed somewhere. Not sure how to debug a problem like this.
Thanks in advance for any help you can provide.
John
Replies
The K&T I see is all one color - never seen it with white before.
Early K&T was sometimes fused on the neutral side.
A personal opinion: if you are working on old (or any) wiring without 100% knowing whether it's live, you don't know as much about wiring as you should to be doing a job like this.
_______________________
Why Don't Blind People Like To Sky Dive?
Because it scares the bejabbers out of the dog
Your mileage may vary ....
Both the hot and neutral wires are black, but the ones in the panel that are neutral appear to have some sort of white paint over the black which has deteriorated over time.
I probably should have connected all the wires before energizing the subpanel but was pressed for time ... we were done for the day and I wanted to get the lighting back on in the lower portion of the house where we're living.
John
The older portion of the house has (well, had, until I removed it ...) a fuse box with 5 fuses. The fuse box was fed by dual 12 amp wires, providing power to fuses from 15 tro 30 amps.
John, we need a little more info here.
The older portion of the house had a fuse box. was this a subpanel? Does it have its' own ground rod or bonding wire to a pipe?
dual wires? was one wire a return neutral, or were both hot? There's gotta be a return neutral, but you don't mention it????
12 amp wires. 16ga or 12 ga? 16 ga wires are close to 12 amp rated, but I'm thinking that you meant 12 ga, not 12amp.
Even with 2 12ga feeders and a return neutral, this box would only be rated at 40 amps total. you can not trust that any of the fuses are the size were originally intended. the breakers MUST be sized to the wire guage that they are protecting.
one of the wires coming into the box (one that I'd disconnected) was hot
why did you not reconnect it before energizeing the panel? maybe it was a return neutral and is being backfed thru a load.
SamT
Sorry for the mistakes in my question. It was late and I was tired.
The wires were 12 ga, not 12 amp. The fuse box was a subpanel which was fed from a new main breaker panel installed about 8 years ago. The main panel has a dual 20 amp breaker feeding the subpanel.
The fuse box was fed by the two hot leads and a neutral ... no ground. I'm going to be running the ground today. That won't help for any of the old circuits, but I've rerun new wire for all of the lights upstairs and capped the old K&T wires. No additional load but some new wiring.
As I said, the five original fuses were rated from 15 to 30 amps. I realize that this is logically overfusing 1 or more circuits. The wiring size of the K&T is a combination of 12 and 14 ga wire (15 and 20 amp circuits). I'm installing breakers consistent with the wire size of the circuits. In fact, I may just install 15 amp breakers to be safe.
And here's a little more info on the "disconnected wire" that showed up as hot when I touched it. I used my multimeter and got 120 volts when I measured between that wire and the neutral buss bar. That tells me that it isn't a neutral wire ... or am I mistaken here?
I'll probably start troubleshooting this one later today or tomorrow.
John
And here's a little more info on the "disconnected wire" that showed up as hot when I touched it. I used my multimeter and got 120 volts when I measured between that wire and the neutral buss bar. That tells me that it isn't a neutral wire ... or am I mistaken here?
It sounds like a neutral. When you energize the hot conductor in a completed circuit (could be just a light bulb making the circuit), the neutral conductor will be at the same potential as the hot (assuming it isn't landed on the neutral bar) as long as no significant current it flowing. It's no different than taking a long hot from the breaker, running it through the house, back to the panel, and measuring potential from that conductor to the grounded terminal: it'll measure 120V. A light bulb filament or motor winding will complete the circuit, and the high impedance won't matter as long as no current is flowing.
As a water analogy, think of an extremely long garden hose, maybe with some severe restrictions in it. With the supply end at 60 psig, and the other end open to atmosphere (0 psig), water will flow slowly, and the end of the hose will be at 0 psig, for a 60 psi pressure difference. When you cap off the end and completely stop the flow, the pressure at that end will build to the same 60 psig as the supply end, for a 0 psi pressure difference. An ungrounded neutral conductor with 120V at the breaker and some load to complete the circuit will yield 120V difference between the neutral conductor and the neutral (grounded) bar in the panel.
That neutral conductor you have, if that's what it is, is connected to something that's energized, and possibly tapped off another circuit. It sounds like you have a real mess on your hands; proceed with caution, or better yet, hire an electrician who does lots of old work to map it out for you and develop a plan of action. I hate to think what's going on inside those walls.
Be seeing you...
Edited 9/30/2003 12:45:56 PM ET by Tom Kanzler
with old K&T wiring you are best off pulling all new wires, messing with it is going to be VERY complicated, as they often daisy-chained circuits with the hot and neutral not even running to each device in similar ways - you can go nuts trying to reverse-engineer one of those. And if anyone has done any splicing or modifications over the years it may be quite unsafe and dangerous as well (un-molested K&T, with no insulation on top of it, can be safe as long as it is not overloaded and never touched).
My advice is to take the hit and re-wire the whole schmeer.
Not what you want to hear, but this is based on experience.
Norm
Tom, and the others who've replied, thanks much for the input. I expected the advice to rewire the whole house. Not sure what my son will say to this as it may involve more tearout than he's willing to do.
One more piece of the puzzle ... I checked the existing wires in the box, after turning off the breaker that supplies the two hot legs, and was majorly surprised. There's a wire in the box that is not only hot but it shows 50 volts when tested with my multimeter. This tells me that someone connected wiring from a newer circuit to one of the old ones someplace. I suspect that it's 50 volts because the wire isn't making good contact or has been compromised in some way (cut half way thru for example). Am I close here as to that wire?
At this point I'm just going to sit back, think about what's going on, and not do anything at all. It's probably reasonable to do as more than one of you have suggested ... but this house is lath and plaster as opposed to sheetrock, so the problem is a big one.
John
Plaster-lath. Rough.
Sounds to me like you might be doing a bit of fishing. As in fishing cables through wall cavities. I have had luck cutting in new boxes into such walls with a diamond disk in a 4" grinder. After a few you can cut one in just a few minutes with confidence. Of course this depends on the condition of the plaster so it is never a lead pipe cinch. Particularly if the plaster has been chronically exposed to moisture. In some cases a blowout is the likely outcome even with the best tools and a talented operator. The good news is that given the K&T wiring there is likely to be little, if any, insulation to get in the way. Good luck.
No instulation (you're correct here), and I've already seen lots of blowout on other parts of the construction. If it were my house, I'd take it down to the studs and start over ... :)
John
"I hooked up the power, and ran the wires for two circuits to the breakers and the neutral bar."
I am confused by the TWO CIRCUITS.
You indicated that there where 5 fuses, but feed by two wires?
Was this wired as 120/240 orginally.
If, you just looked up 2 circuits at this time it sounds like you have only powered up the new sub-pannel.
Also note that I have seen pictures where fuses where on both the hot and the neutral.
And I did not see any reference to a ground going to the sub-pannel.
Besides the things that the others have said about k&t wiring with anything this old that there is a good chance that some "creative wiring" has been added. Such as tapping off a hot for a new device and getting the neutral from another circuit.
I think that it is time to strip everything down and start over, but first making up a schematic of just what you have.
That means taking each circuit and finding the not and neutral pair and then finding what is on that circuit. You might be able to do this with an ohm meter, but a tone tracer would also be helpful.
Given the age of the wiring and the difficulty of walking someone through a complicated troubleshooting and repair job remotely, a simple miscommunication can easily cause a fire or get someone hurt, I think your best course of action is to rewire. Discounting the mechanics of getting cables from place to place this is actually pretty straight forward electrically.
The advantages to this approach include ensuring a solid ground system, assurance that some long forgotten splice or frayed insulation isn't going to cause problems and also provides a grand opportunity to add outlets. Given the age of the original wiring I suspect that the house is underwired in terms of the number and spacing of outlets and circuits. The holes cut for any additional outlets also give you better access to the existing boxes so it often doesn't add as much work as it seems.
I blithely avoided the problems of getting the cables from box to box. Knowledge, patience, experience, specialized tools and techniques and no small portion of luck make the job manageable. Notice I didn't say easy. Rewiring a house without butchering the walls and ceilings is as much an art as a science. A few tips:
Removing baseboards and other mouldings, or adding them in some cases, can allow much easier access.
Take advantage of any space you can. A closet is often a good place to run a conduit or two. More than a few runs may justify having a friendly carpenter assemble a chase. Attach the face with screws to allow easy access later.
Take advantage of Flex bits, four to six foot long flexible bits with provision for pulling wires back. Spend the money for the placement handle. It makes blind shots much easier and accurate.
Groom a helper. Fishing cables requires tight communication skills. A timely call of "touch", indicating that your helper feels his fish tape contact yours, tells you that you are close. A deft twist of the tape or wire can then hook the two ends allowing you to get a fish tape through. headsets and voice activated mikes on good set of walkie-talkies makes things easier.
After you spend a few ours of frustration and have expended you vocabulary of naughty words and vile oaths consider hiring a contractor with experience in old work. Most of them have a far greater vocabulary in such language. Some even have the experienced personnel and techniques to get the job done in good time. This doesn't come cheap but neither does a rage induced stroke or, much more debilitating and expensive, a divorce.