Help With An Open Circuit

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  #1  
Old 02-10-14, 09:21 PM
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Help With An Open Circuit

I had nearly all of one circuit in my house go out the other day for no apparent reason. The circuit in question has roughly 7 overhead lights on it, and unfortunately is on the one remaining circuit in our 1921 house composed of knob and tube wiring.

Lights on the circuit are made up of: one basement light (which curiously still works) with all the wiring exposed to view a dining room, entry and porch light on the middle story with wiring hidden in the walls and two upper story bedroom overhead lights and a hall light with accessible wiring from the attic.

Since the one light working on the circuit is on the basement I'm hoping that the problem is down there. That wiring leading to the two upper stories in the circuit are exposed, and I've bought a multimeter and will be checking voltage at any junction I can find in the basement before the wiring starts running up into the walls. If I find voltage in the circuit as it leaves the basement, what do you suggest I do next?

I was thinking it may make sense to check each of the switches for loose wires. There are still some very old light switches on the circuit; but would a faulty wire in one of these cause the entire circuit to go out? I'm having nightmares that it's one the hot leads in the circuit that has come apart behind one of the walls or in the attic. Hard to image why though since there has not be any remodeling, picture hanging, etc.. going on. In the meantime, I've turned the circuit breaker off. Any help would be greatly appreciated!
 
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  #2  
Old 02-10-14, 09:58 PM
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Welcome to the forums.

The basement working is a good thing. You should be able to trace the wiring thru the basement and to where it goes up the wall. Make sure you have hot and neutral actually leaving the basement.

Since you know which wall the wiring is going up.... that's where you need to check next.

Your problem will be between the last working device and the first dead device. So in your case the problem is probably not in the attic as the wiring should hit the first floor first.
 
  #3  
Old 02-10-14, 09:58 PM
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Be careful...sometimes lights on knob and tube were wired so that the switch was on the neutral wire (and there is no ground). Any modern wiring would have the switch on the "hot" wire.

Having the switch on the neutral wire means that the light fixture is always "hot". Even if the switch is turned off and the light is off, if you touch the "hot" wire, you become the neutral/ground...which means you get shocked!

You need to be using a voltage sensor, not a multimeter. A voltage sensor just needs to be placed up against the wire and it will beep if there is voltage. It is much easier to use, and much safer than a multimeter. I bought a Fluke voltage sensor at Lowes for something like $25. They have them on Amazon, too.

As you probably know, knob and tube wiring has the hot and neutral wires seperate (usually run about a foot apart from each other). So you will have to figure out which wire is the hot wire and which one is the neutral.

Consider buying a circuit tester also. It's a little thing that plugs into the outlet and it has 3 lights on it. It will tell you right away if the outlet is missing the hot lead, neutral lead, or ground (knob and tube isn't grounded anyway). However, they will not work for light sockets.
 
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Old 02-10-14, 10:04 PM
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Don't worry about the wiring in the wall there is probably less then a 1% chance a wire in the wall went bad. You almost certainly have a bad connection either in the last working fixture or first non working fixture. You need to open all the fixtures on the circuit including any receptacles till you find the problem. Any backstabs need to be moved to the screws and all wire nuts removed and connection checked. Inside of wire nut needs to be checked for a broken spring or corrosion. Star at the last working fixture closes to the breaker panel and work out.

Additionally you can use your meter to check for voltage between black and ground and black and neutral. If no ground use an extension cord with ground plugged into a known properly wired receptacle with ground as a reference ground for testing.
 

Last edited by ray2047; 02-11-14 at 01:40 PM.
  #5  
Old 02-11-14, 10:42 AM
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Thanks for the replies. Good comment on the voltage sensor. After posting last night I was wondering how I was going to check voltage with the multimeter with the hot and neutral wires running seperate.

I'm going to investigate the the wiring in more depth tonight after work. A curious thing though; I looked at the wiring and circuit diagram I created long ago before having my old fuse box replaced with a panel, and it looks like the wires for the hot and the neutral start going up through the lower floor and walls at opposite ends of the house. Is that possible? Would'nt they need to be routed in parallel to each device?

Also; as I mentioned in my original post, I have some really old switches that are still connected to the circuit. For example, there is a switch in the master bedroom that turns on the downstairs hall light, dining room light, and porch light. It was a poor man's burglar alarm when the house was built. We don't use it anymore, but seems like these could be problem areas. Would a problem at the switch cause the entire circuit to go out though?

Thanks again!
 
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Old 02-11-14, 01:46 PM
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it looks like the wires for the hot and the neutral start going up through the lower floor and walls at opposite ends of the house. Is that possible?
Now a code violation but occasionally done with K&T.
For example, there is a switch in the master bedroom that turns on the downstairs hall light, dining room light, and porch light. It was a poor man's burglar alarm when the house was built. We don't use it anymore, but seems like these could be problem areas. Would a problem at the switch cause the entire circuit to go out though?
Depends on how it is wired. Bypass the switch and redo any other connections.
 
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Old 02-11-14, 08:48 PM
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I Think I'm Getting Closer

I bought a voltage sensor and have found that I have voltage at each of the lights and light switches that are not working. That would tell me that the problem is in the neutral, correct?

The one light that is working on the circuit is in the basement. The neutral coming from the panel has a branch (that's soldered and wrapped) off to this light in the basement before it leads up through the floor and walls to the other lights on the next two floors that are not working, so the problem is somewhere after it leaves the basement.

I'm a little unsure what to do next. There are no junction boxes on the main floor, so no place for a connection to come loose. I can check the wire nut connections at each of the four floor lights that are on the main floor, but I'm presuming these too may have branches off the main neutral and may not provide the answer where the bad connection is. I can forage around in the attic since the wiring is exposed up there, but I'd assume that the problem would be between the first and second floor. Any suggestions on how best to further narrow down the culprit?
 
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Old 02-11-14, 09:28 PM
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I bought a voltage sensor
If you mean a non contact tester? They are only good for educated guessing. To determine what is wrong you need a multimeter, preferably analog. You may end up having to check every connection, a daunting task. At some point if I didn't find the problem with reasonable effort I'd start running new cable.
 
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Old 02-12-14, 04:19 PM
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There might be a junction/splice hidden inside one of the walls or floors. It's not something you're allowed to do by code anymore, but it was common with knob and tube.

You might want to try running a wire from your breaker box for testing....attach it to the neutral bus bar, then connect the other end at the light or receptacle that you are trying to test. You can also attach the end of the wire to a neutral line inside a box that you know is working (on another circuit). That would save you from having to take a wire from the basement all the way to the second floor.

Also consider that a mouse or something might have chewed through a wire somewhere in a wall. I pulled up a floor board in my house once where a knob and tube junction point was, and there was some insulation chewed off the wire and the skeleton of a mouse laying beside it.
 
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Old 02-12-14, 08:00 PM
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Thanks for the reply. I was thinking the exact same thing about a critter; but more likely something up in the attic. I would expect the problem to be occurring before the wiring gets to the attic; but I've seen some surprising things changing wiring out in this house since we moved in 20 years ago. I'd love to nuke this last K/T circuit; but there's a reason it's the last one in the house. It only has overhead lights on it, and the wiring snakes all throughout all three stories making replacement a struggle.

Thanks for the suggestions.
 
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Old 02-12-14, 09:14 PM
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the wiring snakes all throughout all three stories making replacement a struggle.
You don't replace it. You run news wire in the most logical and easiest way and abandon the old wiring in place.
 
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Old 02-13-14, 08:21 PM
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Yep.....I'm aware of that. Lights for upstairs are a snap. I can easily rewire a new circuit through the attic. Middle floor is the problem. I have to get into ceilings and walls that are skim-coated lath and plaster that are in beautiful condition. Definitely can be done, but with a little pain and expense that goes along with it. Just part of the joys of owning an old house.

However this gets resolved I'll be sure to post the resolution. I really appreciate all the help and suggestions! This is a wonderful site.
 
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Old 02-13-14, 09:00 PM
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Smile fwiw

Just a tip from an old phart...

If you use a NEON test lamp, the type where you can actually directly see the bulb, you can hold one probe tip in your fingers and touch the other probe tip to a bare knob and tube wire. if the wire is a "HOT" wire, you will see the neon lamp glow ever so slightly. The current needed to light the lamp is so little that it can pass through your body and you will never feel it. This test will also work in the attic of a frame house atop a third story!

ONLY DO THIS WITH A NEON TEST LAMP.

To prove my point, try it in any standard outlet by pushing one probe from the test lamp into the smaller prong hole for an receptacle, it will glow slightly when you grasp the bare probe. Even with rubber soled shoes or sneakers.

Just a tip from an old phart....

BTW, I had my first house inspected in May 1970, right before I went in the army for the Vietnam thing. Retired now after 33+ years working with electronics for the government.

Cordially,
Gerry
 
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