1920's Home, Stumped but thats not hard

Status
Not open for further replies.
J

John120/240

Senior Member
Location
Olathe, Kansas
i920's home, Knob & Tube. Single pole switch at front door controls two lights each side of front door. Neither light works, but Volt-Con shows voltage. Install a A 19 incandescent & it blows out immediately in either fixture.

What am I missing ? Major Brain Fart. The answer is so simple but it escapes me. Thank You.
 
John120/240 said:
i920's home, Knob & Tube. Single pole switch at front door controls two lights each side of front door.
Click to expand...

I'm in the middle of a sea of K&T wired single family homes. In my opinion, this two-lights-one-switch arrangement is historically very unusual, and hints strongly that a second light was added to the first.

If this is DIY in origin, it could have been attempted out of the switch location, which most of the time, because of the wiring method, is inherently problematic, that is, either the hot or the neutral is likely to be missing at the switch. Most DIYers will do strange things in this situation, giving rise to the potential for such a failure.

If all the wiring at the three locations is K&T, I'd bring out an extension cord from a good grounding-type receptacle and do some voltage and continuity tests, as those above suggest.

Is there a threeway stairwell switch at the same location? That might be a Carter / Chicago threeway that is miswired. . . giving exposure to 240 V off a second floor circuit that is wrongly on the other side of the panel bus.
 
Sounds like you have 240V across the bulb. Checking center tang to shell voltage of the lampholder will confirm this.

eta: As Al mentioned, it's probably a Carter 3 way, which iirc, turns off the lamp by applying voltage on both conductors, giving 0V potential, IF both hots are on the same leg. Sounds like they are on opposite legs, giving 240V and an insta-blown bulb.
 
JFletcher said:
Sounds like you have 240V across the bulb. Checking center tang to shell voltage of the lampholder will confirm this.

eta: As Al mentioned, it's probably a Carter 3 way, which iirc, turns off the lamp by applying voltage on both conductors, giving 0V potential, IF both hots are on the same leg. Sounds like they are on opposite legs, giving 240V and an insta-blown bulb.
Click to expand...
Back when I was an apprentice, we did a service change from a 120 volt 30 amp service to a 120/240 volt 100 amp service. They had a 3 way like that fed from two different circuits and we got those circuits on opposite legs....same result as here, but my JW knew exactly what was going on and as we fixed it he explained the Carter 3 way to me.
 
Back when I was training we marked every wire with a phase color as they came off the fuses and made sure they went back on the same way in the new panel. Messed up once after I went into business for myself and got educated the hard way with the before unseen three way setup. Took hours and new Romex for the switches.
 
ptonsparky said:
Back when I was training we marked every wire with a phase color as they came off the fuses and made sure they went back on the same way in the new panel. Messed up once after I went into business for myself and got educated the hard way with the before unseen three way setup. Took hours and new Romex for the switches.
Click to expand...
But when you are going from a 120 volt service to a 120/240 volt service and there is a carter 3-way that is fed from two different circuits, you don't really know that when you are doing a service change....not until the lamp is really bright for a very short time:)
 
don_resqcapt19 said:
....... there is a carter 3-way that is fed from two different circuits, you don't really know that when you are doing a service change....not until the lamp is really bright for a very short time:)
Click to expand...

It may "work" but the Carter system has been outlawed for a long time for very good reason.:happyyes:
 
Status
Not open for further replies.
Top