House wiring questions

[supton]

Couple years ago I found this:

I had always assumed it was dead; recently I borrowed a contactless voltage indicator, and sure enough, it can be made live (switched outlet for roof heat tape that got removed long ago). Found it behind what I thought was a heatshield above a wood stove; but I'm guessing that was put up to hide the wire. Best guess, PO was doing wiring over a hot stove. Anyhow, that's a line I want to tap for another outlet, so it's getting fixed. But in doing so, I found something I don't understand.

Question: this circuit (before the switch) runs from the breaker box with 12/3. Both black and red have 20A breakers. Is that legit? It seems wrong to me, since the neutral wire would be undersized. At the end of the line, the red is capped off and goes nowhere. Black goes to the switch, and then runs this (damaged) wiring. I'm tempted to remove the red wire at the breaker box and cap off, and leave a note on the wiring as to what is going on.

For more badness that I have to fix: it's a 20A breaker, feeding a 12g wire, to a 15A switch, with 12g wires running to 15A GFCI's. [Well, the one I can get to is a 15A GFCI, the other outlet is too high up at the moment.] [Well, it's two 20A breakers, but if I cap off the red, the other breaker will be unused.] So now I get to learn how to replace a breaker too. Oh goody.

 

[wheelman1991]

It's 240 vac if the breaker is double.

 

[supton]

Oh duh--that makes sense, a 240 line. I wonder if the line originally went to the stove or something.

 

[wheelman1991]

The little red "double breakers" on the right are for my bedroom heater. (240 volt baseboard heater)the ones on the left are for more heaters and my stove. Large black breaker on the right is for my water heater.

 

[supton]

The two off breakers in lower right are the breakers in question. The red line is the one I want to disconnect; the black line above it ought to be a 15A breaker, to match the 15A switch and 15A outlets. [That or I need to replace the 15A parts with 20A parts.]

All the other red wires are to do with the generator transfer switch. This red wire is the only red wire coming out of the breaker box; the 240 well pump just uses white/black.

 

[wheelman1991]

Either that, or the p.o. figured "well, I have two 120v items that I want to have a separate breaker for each in the same area." The roof tape and some other large load perhaps, for instance 20 amps on one circuit and 15 on the other. The problem with that is they SHARE THE NEUTRAL WIRE! That can (and probably did) overload the neutral wire, and melt/burn the insulation.

 

[Donald]

While it could be 220v it is more likely two 120v circuits. Common way to run less wires. However it is critical that the red and black run to a ganged breaker. The red and black need to pick up different legs of the 220v. If you were to run a 60 watt light between black and neutral and another 60 watt light between red and neutral, the neutral carries no load.

However if by mistake both the red and black are connected to the same leg of 220v the the neutral would carry 120 watts. Which is wrong. Scale it up to a 1500 watt heater instead of a 60 watt light and the neutral now carries 3000 watts and would get hot or glow or burn.

 

[George7941]

3-wire circuits, which share the neutral, are perfectly fine and are used all the time for kitchen counter outlets. The neutral does not get overloaded because the currents in the red and black wires are of opposite phases and cancel each other out.

If you had equal resistive loads on the black and red circuits, the neutral wire carries no current all because the two currents cancel each other out completely.

 

[Donald]

Originally Posted By: wheelman1991
Either that, or the p.o. figured "well, I have two 120v items that I want to have a separate breaker for each in the same area." The roof tape and some other large load perhaps, for instance 20 amps on one circuit and 15 on the other. The problem with that is they SHARE THE NEUTRAL WIRE! That can (and probably did) overload the neutral wire, and melt/burn the insulation.


Read my post, sharing the neutral is OK if things are wired properly. The trouble comes when homeowners get into the CB box and mess things up.

Some people probably should not be posting to these kind of posts.

 

[Joe_Power]

Originally Posted By: Donald
Originally Posted By: wheelman1991
Either that, or the p.o. figured "well, I have two 120v items that I want to have a separate breaker for each in the same area." The roof tape and some other large load perhaps, for instance 20 amps on one circuit and 15 on the other. The problem with that is they SHARE THE NEUTRAL WIRE! That can (and probably did) overload the neutral wire, and melt/burn the insulation.


Read my post, sharing the neutral is OK if things are wired properly. The trouble comes when homeowners get into the CB box and mess things up.

Some people probably should not be posting to these kind of posts.




Gotta agree with The Donald on this one. These armchair electricians will burn your house down. Hope your insurance is paid up...

 

[supton]

Found another oddity: furnace and microwave are on two separate 20A breakers. But they go to the generator transfer switch, which has a switch to remove from house power and switch to generator power. And which uses... 30A breakers. Go figure... Don't have a generator so no rush to fix that one.

 

[tom slick]

If the neutral is shared between two circuits you need a double breaker that is tied together like the one on the lower left. That way not only are the two circuits phased correctly but it always shuts off both circuits.

 

[Donald]

I have a Winco propane generator I can give you a good deal on.

 

[Donald]

I have a Winco propane generator I can give you a good deal on.

 

[supton]

Hmm, lemme think about it. If you could, PM the model number to me, and we can take this to messages.

 

[eljefino]

Originally Posted By: Donald
Originally Posted By: wheelman1991
Either that, or the p.o. figured "well, I have two 120v items that I want to have a separate breaker for each in the same area." The roof tape and some other large load perhaps, for instance 20 amps on one circuit and 15 on the other. The problem with that is they SHARE THE NEUTRAL WIRE! That can (and probably did) overload the neutral wire, and melt/burn the insulation.


Read my post, sharing the neutral is OK if things are wired properly. The trouble comes when homeowners get into the CB box and mess things up.

Some people probably should not be posting to these kind of posts.



The picture of the Romex (tm) in question shows typical 2 conductor wire, so the ground wire is being used as a neutral, which is a no-no. One needs special 12/3 instead of 12/2 and this ain't that. 12/2 lays flat like a tapeworm, 12/3 looks twisted like a rope.

OP, if you pulled all your breakers and watched where power comes in, the buss bars will zig-zag down and cross each other so if you have two adjacent breakers (listed ok on the box's inside label) they're guaranteed to be opposite phases, so you can stick a double breaker in and get 220 for your stove, dryer, etc.

The 30 amp breaker on your gen transfer panel is vestigial for the panel's benefit so it can meet code. You shouldn't expect to pay any attention to it.

What you have now is pretty sketchy.

 

[Mr Nice]

Hire a licenced electrician and have upgrade done correctly.

 

[supton]

I pulled the red wire from the 12/3 and capped it off. Now it's a 12/3 running power to the switch, but only white/black/GND are connected to anything. Later on I'll swap from a 20A breaker to a 15A breaker, when no one is home and I can cut power. The breaker is left unused.

For now it's actually still dead on the 12/3, since it's not needed, and I haven't fixed that melted wire yet. Later this week.

If it's a big to-do to have this 12/3 wire with a dead red wire, I'll pull it. I made sure to leave a rope in the wall so I can snake a wire up to the electrical box (spent a few hours negotiating 5').

 

[Wolf359]

Originally Posted By: George7941
3-wire circuits, which share the neutral, are perfectly fine and are used all the time for kitchen counter outlets. The neutral does not get overloaded because the currents in the red and black wires are of opposite phases and cancel each other out.

If you had equal resistive loads on the black and red circuits, the neutral wire carries no current all because the two currents cancel each other out completely.


Electrical engineer here. There are too many armchair electricians on this thread. I believe you're right and everyone else doesn't really know what they're talking about.

Sounds like OP really has 12/3 which would be a black, red and white wire plus the ground wire. If it were 12/2, he wouldn't have the red wire, just a black and white wire plus ground. Electricians did this type of wiring all the time. It saves you from having to run 2 lines. You just have to remember to keep them next to each other so that they're on the opposite waveform. The only problem with this type of set up now is that you need a separate neutral wire if you're going to run an arc fault breaker, doesn't work on these types of 12/3 wiring jobs. Incidentally, the same thing could be done with 14/3 wiring. Saves you from having to run extra wire. Handy if you have two bedrooms next to each other, one circuit can go to one bedroom the other the bedroom next door and you just run one wire.

 

[supton]

Been eons since I looked at power factor; was never my field of study. So I tossed something together to simulate. 1A loads, arbitrary power factor of +0.8 and -0.8 for the two loads.


This gets a neutral current of about 0.4Arms, or about four-tenths of the load current.


Then for fun, I modified it from purely capacitive to something more normally seen, a bridge and capacitor.

This has a smoothed voltage of about 160V, kinda arbitrary.


Anyhow, that leads to some pretty high neutral currents.



Err, it's been too long since college to figure out the RMS value on that waveform. I don't think it's that high actually, maybe 2Arms if I squint. If I get a chance later I'll have to go and "remember" how to do that bit of math.