[NA] Adventures in 100-year old house wiring

schmookeeg

schmookeeg

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Mike Brannigan
Hello. :)

I encountered an electrical issue last night in my 100-year old house which has mystified me, and was curious if someone better at AC Electrics might know what on earth is going on here.

It started by trying to fix my doorbell transformer. The old one showed no voltage despite solid 120V in the wiring it was attached to. I bought a new one.

Upon installing the new one, it too showed no voltage on the low side. I re-verified the 120V on the high side. This is where the rabbit hole began.

I tried finding the breaker to this little junction box, none of the house breakers would kill the circuit, save the 200A main. So I shut off the whole house.

What I found after some deft Volt-Ohm meter work:

X8hCxdc.jpg


Two hot 120V circuits, both wired together. :eek:

My entire office and its lights and outlets and 6 computers running out the top left from this unbreakered fire hazard. :eek:

In my mind, joining two separate "hot" circuits is akin to crossing the streams and a no-no, so my first mission was to cap one off.

I capped circuit "B" first, wired everything back together (black wires together, neutral wires together -- as I had found everything)

...and... it's worse. Transformer remains dead. My entire office is now also dead.

So I reverse course, cap circuit "A", re-wire everything together.

And my office works.

And my stupid doorbell transformer now works. Presumably the old one is just fine as well.

And it only cost me about 4 hours of pecking around in the dark on a ladder in my office closet with a VO Meter last night.

....huh?

So, I plan to test breakers again, thinking maybe only one of the "hot" circuits is breakered, and the un-breakered circuit was foiling the breaker protection.

But I can explain nothing else, including why the transformer will only power on one of the circuits, and why my office will only power on "B" , but not "A" -- both measured 120V. "A" on its own would not even power my 10W ikea desk light after I shut off everything else.

Appreciate any thoughts, as I'm at the end of my AC Electric knowledge, which was not much to begin with. :D I am not remotely happy about having an unbreakered circuit running around the house, so that will be the next step -- to figure out how/why that happened.

(Hell, I'd be happy to get some Google Search Terms so I can learn on my own, but I have been unsuccessful thus far)

Cheers,

- Mike
 
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If the wire is run close enough to other wires it may well show voltage on a sensitive digital volt meter. Use one of those old fashioned neon lamp testers to see if it's really powered.

(or downstream of a switch or breaker that's technically 'off')


Also, double check that it's not the neutral that's open(once again, with a load).
 
With the wires in the box all unhooked and separated as they are in the pic, when you turn the breakers on, does anything on the rest of either circuit work?

If no, then a good chance both wires run from your circuit panel to that box and then go elsewhere.
If yes, the one or both wires make other stops before getting this box. Look inside those other boxes to make sure everything makes sense before pulling out too much hair.
 
And I'll second that a multimeter will fool you. They are so sensitive they will show 120V with no neutral, just a bit of wire. I assume when you say both were 120V you had turned the main back on? Did you check from A hot to B hot? Was that 0V or 220V?

My guess is B is the real feed. A feeds something else you haven't yet discovered.
 
jsstevens said:
And I'll second that a multimeter will fool you. They are so sensitive they will show 120V with no neutral, just a bit of wire. I assume when you say both were 120V you had turned the main back on? Did you check from A hot to B hot? Was that 0V or 220V?

My guess is B is the real feed. A feeds something else you haven't yet discovered.
Click to expand...

Thanks -- I had no idea that voltage could be "fuzzy" on a meter -- and my VO meter is a piece of junk from home depot. If you're right that the capped off circuit killed something else in the house, then I definitely still have an unprotected circuit, which doesn't sit well a bit.

I am going to grab some testers and other gewgaws this weekend and see what I can sort out as the true story. I will probably also generate a map of "this breaker does this" for the whole blooming place. I think half of my panel is labelled "lights and plugs" -- super helpful in a 5 bedroom house. :D
 
schmookeeg said:
Thanks -- I had no idea that voltage could be "fuzzy" on a meter -- and my VO meter is a piece of junk from home depot. If you're right that the capped off circuit killed something else in the house, then I definitely still have an unprotected circuit, which doesn't sit well a bit.

I am going to grab some testers and other gewgaws this weekend and see what I can sort out as the true story. I will probably also generate a map of "this breaker does this" for the whole blooming place. I think half of my panel is labelled "lights and plugs" -- super helpful in a 5 bedroom house. :D
Click to expand...

Yeah. Relabeling the whole panel is probably overdue. Home Depot sells a Klein circuit tracer tool for not too much money. It puts an RF signal on the wire that the receiver can read in the panel. It'll save you a lot of time.

How did you determine that A was hot?
 
jsstevens said:
Yeah. Relabeling the whole panel is probably overdue. Home Depot sells a Klein circuit tracer tool for not too much money. It puts an RF signal on the wire that the receiver can read in the panel. It'll save you a lot of time.

How did you determine that A was hot?
Click to expand...

Main breaker on, very very carefully touching the VO probes to the copper while in 200 AC mode, and showing appx 120V :)
 
schmookeeg said:
Main breaker on, very very carefully touching the VO probes to the copper while in 200 AC mode, and showing appx 120V :)
Click to expand...

So one probe on the black wire (copper part) and the other probe where?
 
Puzzling but I’m still reasonably sure B the real feed
 
kyleb said:
I've saw this with a kitchen remodel I did about a year ago. It really baffled me.
Click to expand...
I use a non-contact voltage tester before I touch anything. I had some electricians run a wire for my new projector but no outlet since I didn't have the exact location. Went to put the outlet on, showed hot, turned off the 'TV' breaker and it went off. Added the outlet, turned on the breaker and nothing. Turns out they did properly leave the other end in the other wall box disconnected and capped and I was just seeing the induced voltage.
 
With all the money u save u can buy some new tools starting with a good ac dc clamp style amp meter like a fluke 325. Works on twelve volt systems like your car too tests voltage, current draw, continuity and more. I love mine have one at work and home. Like wind without an indicator u cant see electricity be careful. As a well driller i deal with electric motors eveyday...electricity can bite hard
 
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Notrub said:
As a well driller i deal with electric motors eveyday...electricity can bite hard
Click to expand...

Back in school, I changed out the ancient outlets in my dorm room. Being the RA, I had a key to the breaker box, and turned off the breaker before beginning the swap. Imagine my 60 hertz surprise when I found a live circuit with my (borrowed) screwdriver.

"Sorry man. Your screwdriver broke."
 
A house doesn't have to be 100 years old to have stuff like this happen. Our house in San Jose was built in the mid 1960s. There was a circuit in the kitchen that was fed by two circuit breakers, one on each end of the feed. You had to open two breakers to kill the circuit. Then one time when a water pipe sprung a leak the plumber replaced a length of pipe with plastic, rendering the green wire safety ground (and neutral) ungrounded. Took out a power supply in a printer with that one.

I suspect it is time to ring out the wiring in the whole house and get it right. Have fun!
 
schmookeeg said:
Hello. :)

I encountered an electrical issue last night in my 100-year old house which has mystified me, and was curious if someone better at AC Electrics might know what on earth is going on here.

It started by trying to fix my doorbell transformer. The old one showed no voltage despite solid 120V in the wiring it was attached to. I bought a new one.

Upon installing the new one, it too showed no voltage on the low side. I re-verified the 120V on the high side. This is where the rabbit hole began.

I tried finding the breaker to this little junction box, none of the house breakers would kill the circuit, save the 200A main. So I shut off the whole house.

What I found after some deft Volt-Ohm meter work:

X8hCxdc.jpg


Two hot 120V circuits, both wired together. :eek:

My entire office and its lights and outlets and 6 computers running out the top left from this unbreakered fire hazard. :eek:

In my mind, joining two separate "hot" circuits is akin to crossing the streams and a no-no, so my first mission was to cap one off.

I capped circuit "B" first, wired everything back together (black wires together, neutral wires together -- as I had found everything)

...and... it's worse. Transformer remains dead. My entire office is now also dead.

So I reverse course, cap circuit "A", re-wire everything together.

And my office works.

And my stupid doorbell transformer now works. Presumably the old one is just fine as well.

And it only cost me about 4 hours of pecking around in the dark on a ladder in my office closet with a VO Meter last night.

....huh?

So, I plan to test breakers again, thinking maybe only one of the "hot" circuits is breakered, and the un-breakered circuit was foiling the breaker protection.

But I can explain nothing else, including why the transformer will only power on one of the circuits, and why my office will only power on "B" , but not "A" -- both measured 120V. "A" on its own would not even power my 10W ikea desk light after I shut off everything else.

Appreciate any thoughts, as I'm at the end of my AC Electric knowledge, which was not much to begin with. :D I am not remotely happy about having an unbreakered circuit running around the house, so that will be the next step -- to figure out how/why that happened.

(Hell, I'd be happy to get some Google Search Terms so I can learn on my own, but I have been unsuccessful thus far)

Cheers,

- Mike
Click to expand...

Don't know how this will all lay out with what you have. But two circuits can share a neutral as long as the hots come from different busses. I assume you have 240v service. Kinda sounds like A just doesn't go to the breaker box. Is anything else anywhere in the house dead when you cap one circuit off?
 
luvflyin said:
Don't know how this will all lay out with what you have. But two circuits can share a neutral as long as the hots come from different busses. I assume you have 240v service. Kinda sounds like A just doesn't go to the breaker box. Is anything else anywhere in the house dead when you cap one circuit off?
Click to expand...

Donno yet -- I bought a breaker finder, there are a gozillion outlets in this house. It will take weeks, but I will be leaving a detailed map in the breaker box of exactly what does what. It will likely only benefit the next homeowner.

What's funny is, by capping the "A" circuit, I now have normal breaker function for my office and my computers. So this was a positive discovery regardless.

I still can't explain why hooking "A" to the mix killed off the transformer for the doorbell, though. :D All I wanted was a doorbell. !@#$%
 
schmookeeg said:
Donno yet -- I bought a breaker finder, there are a gozillion outlets in this house. It will take weeks, but I will be leaving a detailed map in the breaker box of exactly what does what. It will likely only benefit the next homeowner.

What's funny is, by capping the "A" circuit, I now have normal breaker function for my office and my computers. So this was a positive discovery regardless.

I still can't explain why hooking "A" to the mix killed off the transformer for the doorbell, though. :D All I wanted was a doorbell. !@#$%
Click to expand...

I'm beginning to think A and B are not different circuits, that's just a 'midstream' junction box. It's unusual to have two circuits in one box with the same color. Usually ones Red and the other Black. If all else fails there's https://www.google.com/search?client=firefox-b-1-d&q=battery+doorbells
 
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schmookeeg said:
Donno yet -- I bought a breaker finder, there are a gozillion outlets in this house. It will take weeks, but I will be leaving a detailed map in the breaker box of exactly what does what. It will likely only benefit the next homeowner.

What's funny is, by capping the "A" circuit, I now have normal breaker function for my office and my computers. So this was a positive discovery regardless.

I still can't explain why hooking "A" to the mix killed off the transformer for the doorbell, though. :D All I wanted was a doorbell. !@#$%
Click to expand...
Apparently you were directing the magic smoke contained within the wires to the wrong place. :) Just be sure to not let the smoke out or you will have an electrical fire.
 
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