electrical horror show
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hockeypuck
Feeling the Heat
nothing like screwing up every wire in the house. time wise it might be faster and safer to rewire the house one room at a time
Warning minor hijacking ahead. Ran into a new one at work, had an old vfd fail (250 hp motor) and before we started troubleshooting management had already decided we should bypass the drive and just run the motor off of a 400 amp breaker only...politely told them where to store that idea. Long story short 2 hrs later the drive was repaired and running. The question is does anyone know what code/reg that would have been breaking other than not having controls within sight of the motor?
Check out part III of article 430
Edit nevermind I just saw it's 250hp.. maybe 400 amps is fine
besides having a disconnect at the device the circuit breaker unless rated for it can not be used as a switch
Highbeam
Minister of Fire
Other than the FP boxes, the other bad guy is a zinsco panel. First home improvement project at this house was a panel swap from a zinsco.
So ... going back to my OP, I finally figured this one out. To clarify the OP, the luminaire is upstairs in a loft, one switchbox is downstairs, and the other is up in the loft. As I noted later (post #23), there was a black-jacketed cable leaving the downstairs switch box, but no black one coming into the upstairs switchbox; most troubling, suggesting a buried splice. On a hunch, I had a look at a downstairs luminaire that was more or less between the two switch boxes; this was enlightening.
What they did was to run two 12/2 cables from the downstairs switchbox to the downstairs luminaire. One had neutral and the switched load for the downstairs luminaire; the other was two travelers, either of which could be connected to hot by the downstairs 3-way switch. Then in the box for the downstairs luminaire, they connected the neutral and the travelers to a 12/3 cable that runs up to the upstairs switchbox. Finally, the 3-way switch in the upstairs switchbox was connected wrong, with one of the travelers (instead of the load wire to the lights) connected to the common terminal. So turns out that re-wiring that switch is all that was needed.
This seems like a pretty irregular way of wiring a luminaire controlled by two 3-way switches - I would have just run a 12/3 between the two switchboxes (with neutral and the two travelers), bypassing the downstairs luminaire - but I guess it's ok.
Unlike some of the other things noted in my OP, this seems like it was probably done by the OG (original electrician). And it (the wrong wiring of the upstairs switch, not the odd way the cables were run) suggests that he was an idiot.
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Sounds like they ran out of /3 wire and got creative. Not how I would do it either because it wasted people's time while they scratch their heads over it.
Technically, you're supposed to keep the sum of currents in a cable at zero. The two travelers by themselves is a code violation unless it is NM cable and all of the boxes in the circuit are plastic. See 300.3(B)
Potentially overfilled the box at the downstairs luminaire as well.
Well, yes, it IS Romex and the boxes are all plastic (I think, can't get into the one for the upstairs luminaire, which is a tracklight). I can't quite tease what you said out of that NEC reference.
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Good then you have nothing to worry about. 300.3(B) is saying that you need to keep all conductors of a circuit within the same conduit or cable. The idea being that if you run hot and neutral along different paths, you will create a loop that generates electromagnetic interference and in the most extreme cases can actually heat up the conduit due to eddy currents. Running all conductors in the same conduit causes the currents to cancel out so you don't generate any radiation.
Note that a regular switch loop (with hot and switched hot) is compliant with this rule even though there's no neutral wire.
The exception is in 300.3(B)(3). Nonferrous (NM) wiring methods are less susceptible to heating up so the NEC allows them to be in separate cables.
However the EMI issue is still present and could wreak havoc on electronics depending on how big the loop is and how much current is flowing. For two cables bundled together feeding a light, it's not a big deal.
Yeah, I have no reason to believe the two 12/2 cables aren't pretty close together in the short trip from downstairs switchbox to downstairs luminaire. I guess what matters (for EMI) is the area described by the loop they form, and I believe it's pretty small (as will be the current, after we put an LED fixture in there). But I'll have a notion where to look if they see weird stuff.
another weird thing is they used 12 wire instead of 14. not that it is a code violation but hard to stuff in all that 12 ga and a dimmer into a switch box
They typically wired the lights and outlets in a given room on the same circuit, and I guess they wanted a 20amp circuit for the outlets.
Come to think of it, I'm not sure that's 12awg in those boxes. Better check that. Wouldn't put it past 'em to use 14awg on a 20amp circuit. I could put in a 15amp breaker ... oh, except it's an old Federal Pacific panel.
hockeypuck
Feeling the Heat
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