My 10 year old house has an in-law suite in the far opposite corner of the house from the service panel. There are a total of 12 duplex receptacles, 3 ceiling lights rated to 180W each (3x60W), bath light to 480W (8x60W), and a bath fan (probably 50cfm, unknown current draw), all on a single 15A circuit with 14 gauge Romex. That’s about 1000W of (possible) lighting plus fan plus whatever is on the receptacles.
The problem is that the first box in the chain is about 100′ from the panel, with the last an additional 40′ from the first, going around the outside wall. Turning on a vacuum cleaner pulls the lights down more than I’ve ever seen before. Even a small television or a computer causes a distressing amount of dimming. I’ve measured 121V unloaded, dropping to 104V with lights, TV, and vacuum on, measured at the last receptacle. I’m currently modifying a wall to fully close off the back room of the “suite” with a door, temporarily exposing one of the device boxes in the process. It’s about half way around the chain.
Since I’m already in the wall, what would be the best fix for this problem? Break the circuit in half with a new home run (12 ga, perhaps) to the exposed box? Not break it in half but still run a new 12 ga HR, abandoning the existing 14 ga HR (I could divert it to the garage with little effort)? 2 new HR’s? And is it legal to have a 12 ga HR with 14 ga after the first device box (still on a 15A breaker, of course), and if so, is there a standard method of marking the 12 ga in the panel so nobody changes it to 20A unwittingly?
Sorry if the question is wordy, but it seems lots of questions suffer from too little info.
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Replies
One of the criteria for sizing wiring is for voltage drop. It is perfectly legal and proper to upsize the wire when you have a long run.
What you could do is to slip a band of the cut off sheathing over the end of the wire in the pannel and then use a magic marker to flag is a 15 amp circuit.
What I would so is to run 2 #12 circuits. Take all of the bathroom load and put it one. I don't know if that is practical, because you need to rewire the lights and fan along with the outlet for #12 and put it on a 20 amp breaker. That brings the bath upto current code.
Then put all of the remaining lights and receptacles on the other circuit and keep it on a 15 amp breaker.
Thanks for the prompt reply. What I didn't make clear is that the bath GFCI is on it's own 20A, shared with an adjacent bath GFCI only. But the lights and fan are with the other rooms.
Sitting here looking at the exposed box with incoming and outgoing cables exposed, it would seem to be a good canditate for 12-3, common neutral, with each leg going to half the devices. As I said before, the exposed wiring is about at the mid-point. I could redirect the existing HR to the garage, or just hold it in reserve. Basement access is excellent. My hesitation would be the common neutral. There are already two circuits in this house wired that way, and I'm not sure I like that. If someone moves a breaker to the same pole as the other, the neutral can (will) overload. Maybe just 2 runs of 12 ga with 15A breakers. Any further thoughts?
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"What I didn't make clear is that the bath GFCI is on it's own 20A, shared with an adjacent bath GFCI only. But the lights and fan are with the other rooms."
Good. You have two options on bathrooms. One 20 amp circuit that feed several baths, but only the outlets. Or one circuit per bathroom and that also do the lights and fan,
"There are already two circuits in this house wired that way, and I'm not sure I like that. If someone moves a breaker to the same pole as the other, the neutral can (will) overload."
A number of people don't like shared neutrals for that reasons. But I still think that they are OK if handled propery. But I found one in my house that was screwed up. My guess is that the HVAC people did this, but it might have been the electricians helper. I found this while tracing out another program where they really screwed up bad. Anyway I have two furnaces side by side and 2 circuits, shared neutral, was run for them. Then someone tied the two hots together, tied it to one switch, then feed the two units, and swaped one of the hots at the pannel to get both on the same leg.
Anyway in your case you are all ready doing something out of the norm by using #12 to feed 15 amp circuits. I would go ahead and sleave it like I said, but mark it as a shared neutral 15 amp circuit. That should give plenty of notice that this is "different" and not to mess with it. Anybody that would ignore that would go ahead and put in a 30 amp breaker and try to run a drier off of it anyway.
Can you get dual 15A breakers? That would at least reduce the chance of someone later putting both sides of the circuit on one leg of the 240V.
Panel is Square D with QO breakers. I believe 2-pole 15A are available. But the downside is obviously that if one trips, they both trip.
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There is that. I forgot breakers do actually trip sometimes. :)
I was thinking of a common neutral application for adding circuits to make one of my bedrooms into a computer room. The only reason I was considering the common neutral was because I had a nice piece of three conductor cable in hand. I was going to put a dual 25A breaker in the breaker box and separate 20A breakers at the load end, so I would expect that the 20A would always trip first. But the cable turned out to be 3' short and I decided to just put in two separate 20A circuits.
"I believe 2-pole 15A are available. But the downside is obviously that if one trips, they both trip. "
I ain't normally one to argue - Especially sine I'm not an electrician. But are you sure about that? I haven't used dual breakers much, but thought they were completely independent of each other.
I know the big breakers like the ones for clothes dryers have a "dual handle" that would make both of them trip. Is that what you guys are talking about? Or is it the "skinny breakers", so you can double them up in one breaker space?
Q: Why do gorillas have big nostrils?
A: Because they have big fingers.
The two-pole type I'm referring to have the double handle, or in the case of Square-D QO style, a single handle on one side of a two space breaker, and they are available in 15A. They are the same as the big breakers for clothes dryers and such you are referring to, but with a lower current limit. But since each circuit is independent, they don't have to be tied together, in fact it's better that they're not, so I'm using two independent 15A breakers. Only the neutral is common, and therefore they must be on opposite poles or the neutral would take the "return" current of both circuits, potentially 30A, rather than cancelling each other. Those half-space, or "skinny" breakers you are referring to have both circuits on the same pole, but you are correct in saying that they are independent. And besides, I have plenty of space in the panel (200A and only half full).
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Thanks for clearing that up. I was just a bit confused.
But at my age, that's normal...................(-:
No sweat. You caught me on a day when I myself wasn't a bit confused. It seems I don't have as many of those in a week as I used to. I'll be asking you a truss question in a couple of days (after I get back into the attic to measure), since I've never seen you confused about that subject. If you wouldn't mind.
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The major hazard of this configuration is not that both circuits will trip if one overloads. They make flashlights for this eventuality. The real hazard is what happens if you loose your neutral connection. Loosing a exhaust fan motor or florescent ballast may be the least of your problems. For an extra 5 cents a foot I try to avoid the potential problem. Three wire cables have their place. IMHO this is not one of them.
Thinking about it with the crystal clarity of hindsight, I probably could have just run a single 10-2-G 100' HR to the exposed box (still cutting off the existing 14ga HR), and been done with it. Voltage drop would be even less than it is now, which is a big improvement as it is, and the labor would have been about the same. But what I'd like to know is, how could an electrician (same one who wired the other 14 houses in this development, I presume) knowingly run 140+ feet (to the last receptacle) of 14ga when the result will be a huge voltage drop under load. I thought there was a maximum permissible value (5%? 6%?). But then, all the switches and receptacles have backstab connections only; no screws even exist on the receptacles. And they didn't pigtail the conductors when they wired them; they're chained together using only the backstabs. So I suppose I shouldn't be surprised.
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Sounds to me that the real problem is not the home run but the need to split the circuit and the connections at the receptacles. You have split the circuit. Replace the push in abortions with high quality units with wrap and screw or clamp type connections and you should be all set. 280 ft , 140 times 2, of run should not have been giving you this much voltage drop.
Edited 7/23/2002 11:17:39 PM ET by 4LORN1
By way of an update, I ran 100' of 12-3-G, breaking the circuit in half as described above, and using a common neutral. Where there was a 17V (14%) drop before, there is now about 8V (6.7%) , and the other leg is even less, due to the reduced loading. With everything running as before, absent what was separated out, total current draw is 14A, but that includes the 7A vacuum cleaner. I seem to recall that 6% total voltage drop was code, which would require 10ga, but I could be wrong.
I marked the conductors in the panel as you recommended, with one breaker right over the other (opposite poles) and the sleeve practically touching the breakers. It would take a deliberate act for someone to put them on the same pole. I also marked the other (pre-existing) common-neutral pair the same way.
Thanks to you and Uncle Dunc for the good advice.
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As others have suggested, it sounds like a good time to pull and replace all those duplex outlets with screw types. I sure hope they left enough wire in each box (per code) to do that. I suspect you might find the same for all the other outlets in your house (hint, hint). I doubt whomever did this suddenly decided to do things better. One of the first things I did was to map out every single fixture, device, and receptacle in the house to its breaker. I also marked every J-box as to what breakers went through it. This is all in a nice computer file which will be given to the next owner. I discovered some real hazards by doing this. In fact, when I read your first report, and all I could think of was what would happen when a hair dryer was connected to this circuit. I guess my favorite was a bathroom addition GFI receptacle. The GFI was added (literally in-line) to an existing branch circuit which supplied all of the light fixtures on the first floor and a couple of ungrounded duplex receptacles on the second floor. And the ground for this? Well, the metal tab of the GFI receptacle was screwed tight to a piece of wire which was screwed to the metal box, and another wire off the metal box was connected to a nearby cold water pipe.
I have been replacing switches and receptacles as each room is painted, making new pigtails, and using screw lugs on the new devices. I've done about 3/4 of the rooms to date, including the subject guest rooms, and only have the dining room left. It takes longer to make pigtails, but I'm much more comfortable with the results.
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