Turns out the inspector really can't see through walls
September 18, 2011 3:40 PM   Subscribe

Why would nearly all of a 1940s-era house be run on two 15-amp circuits?

You are not my electrician (I'll be getting one soon).

I just bought a 1940s house. As it turns out, I have three cables of BX wiring and multiple strands of Romex heading into the breaker box. All of the BX is on 15-amp circuits, while all of the Romex is on 20-amp circuits.

One strand of BX feeds the entire front half of the first floor of the house -- receptacles and overhead lights (about 10 receptacles, about 15 total overhead bulbs). Another strand feeds everything else in the house that isn't GFCI: the entire back half of the house, basement lighting and the finished half-floor upstairs (probably about the same load as the first strand).

Both of these are 2-wire BX, so there's no ground. Oddly(?), the third strand of BX does have three wires (black, white, red), but BOTH the black and the red are hooked up to 15 amp breakers. all three head up into the house at the same place, whereas the Romex wanders all over the basement before heading up through the floor.

Is it normal for the whole house (aside from GFCI) to be run on 2 15-amp circuits? And whats with the three-strand BX where two strands are hot?
posted by brentajones to Home & Garden (10 answers total)
 
In our 1947 built house that we bought in '08, we had three fuses for the house. It appears that someone replaced knob-and-tube at some point, all the breakers are run with 2 wire NM under the house, while the lights are still on a hybrid up in the attic. We had lights, one kitchen and bathroom mixed, and one for all the rest of the sockets.

My guess is that the BX is original, and the NM/Romex is a retrofit. And that you have lights on the same circuit as outlets says that the retrofit was done by a homeowner, not an electrician.

On the "both strands hot", are the black and the red hooked to the same breaker or fuse? Reasonable practice would be to either share the neutral with two circuits (like you'd do with /3 NM) or use it for a 220v stove or dryer circuit.

First thing we had done when we bought the house was a new 200A drop and breaker box, and on my list is running grounded NM to the sockets, and rewiring the lights.
posted by straw at 3:56 PM on September 18, 2011


That's about what my 1950-built house was like when I moved in. (I actually had to get the circuit box upgraded to get insured.) We had one outlet in each bedroom, and like two outlets in the living room ... kinda crazy. Also divided front half/back half. Also with Romex to the kitchen.

We spent around $1500 on the box upgrade and having some three-prong grounded outlets put in (for computers) and some wiring upgraded when we moved in, as well as a few extra outlets; every time we've had an electrician out since then we've had him also upgrade a couple of outlets. If I did it again I'd probably plan to shell out all at once to upgrade the whole system at once, rather than doing it piecemeal. Not that it's been a major hassle or hardship, just that I always have to *check* to see which outlet in the dining room I can plug my computer into (can't ever remember) and it would be nice to have it all uniformly upgraded and nice. (On the flipside, we've been able to put in new outlets as we figured out where we wanted them by going piecemeal over several years.)
posted by Eyebrows McGee at 3:59 PM on September 18, 2011


The two hot wires go to separate circuit breakers? If so I guess they were just being cheap with wire and running two circuits with one run (probably not up to modern spec) or it might be a 220V circuit - do the two hot wires go to different sides of the breaker box?

Anyway, there's no rhyme or reason to old wiring. If it looks wrong, it may be wrong.
posted by GuyZero at 3:59 PM on September 18, 2011 [1 favorite]


Response by poster: I considered the 2-hot strand might be shared (they're on different breakers on the same side of the box), but didn't know whether that was an accepted (or typical, if not accepted) practice.

I /think/ the box is acceptably new -- it didn't raise any flags with the inspector or my realtor.

It's got 4 15-amp circuits (the two as described and two (the 2-strand hot) that I can't figure out).

It's also got 10 20-amp circuits, which I think is enough for every GFCI and 3-prong receptacle to be on its own circuit.

Those are in addition to the larger breakers for the dryer, A/C, etc.
posted by brentajones at 4:16 PM on September 18, 2011


Best answer: I am an electrician. You need to hire an electrician in your area to look at what you have. It can be dangerous to guess about the electrical infrastructure of your home.

That said, here are some thoughts:
Depending on the size of the house, two general use lighting and receptacle circuits probable was enough for code in the 1940s. In the 1940s, power use in homes was much less. And, equally important, electrical material was significantly more expensive then too.. It was expensive to run multiple home-runs for different circuits.

Old wire is does not necessarily need to be replaced. It depends on the condition. You mention that the original BX wire is ungrounded. That is not good, and it might be worth replacing that. If you are going to leave the ungrounded wire, you should install GFCI receptacles. By code, if you have ungrounded wire, you need to either have two-prong receptacles or GFCI receptacles. It is safer to have GFCI receptacles on ungrounded wire.

You need to identify what each circuit does. This is easy to do, it will give you a better understanding of what the electrical infrastructure is like, and it will make you seem like you know what you are talking about when you hire an electrician. Turn one circuit off at a time. Identify everything that is dead in the house as being on the turned off circuit. Label the panel. Then turn off another circuit, and repeat.
posted by Flood at 5:00 PM on September 18, 2011 [2 favorites]


Best answer: Two general circuits for plugs and lights was very common in the 40s. People didn't have much in the way of electrical appliances so as long as they had a plug and an overhead light in each room they were good to go. At 12 outlets/lights per circuit two circuits would handle 12 rooms or say eight rooms with a few extra outlets in the kitchen.

However 10 outlets and 15 bulbs is too many devices on a single circuit unless the bulbs are very low wattage. But if those 25 devices are evenly split over a multiwire branch circuit then you are fine and you actually have two circuits powering those devices.

"the third strand of BX does have three wires (black, white, red), but BOTH the black and the red are hooked up to 15 amp breakers."[...]"whats with the three-strand BX where two strands are hot?"

This is probably a Multi wire branch circuit aka Edison three wire circuit. Two hot legs, one on each feeder, share a neutral. Done right it saves money and in some applications is a code requirement (EG: it is one of two code legal options for kitchen counter plugs in Canada). Done wrong it widely overloads the shared neutral.

straw writes "that you have lights on the same circuit as outlets says that the retrofit was done by a homeowner, not an electrician."

Actually having mixed lighting and plug circuits is very common even on brand new housing. It provides some redundancy in the lighting circuits. IE: if a breaker trips you lose some plugs and some lights instead of potentially all the lights on a floor.

Glad to see you are hiring an electrician. They'll be able to go over what is safe as is, what should be upgraded in some way, and what should be replaced. Fair warning though that the best approach might be at least a new service (drop from the pole, new meter and base, new main breaker panel) depending on what you currently have plus half a dozen new circuits off that panel. At a minimum an outside plug, a dedicated plug for your fridge, a dedicated circuit for your bathroom, and a couple circuits for your kitchen.

Identifying the circuits as per Flood is a good idea and it'll save you money when you eventually get the panel replaced.

Also while you are figuring this out keep an eye out for hidden junction boxes and flying splices (splices not made in a junction box).
posted by Mitheral at 6:10 PM on September 18, 2011


My old neighbor was *cough* "handy" and had meddled-- I mean, "helped" -- with some of the wiring in my house. It was alarming, and to fix it we just added new circuits and shifted over load.

Some of the problems were more than I ever got around to fixing. E.g., one circuit fed the living room, family room, garage door & outlets, outside outlets, motion lights....something else, too, I think. (bathroom? Half of the kitchen? It was a constant source of amazement that we weren't flipping breakers ten times a day.) But running new circuits was about all we could do short of rip-and-replace the whole thing. And in that 1950s Cape Cod, it just wasn't worth it.
posted by wenestvedt at 11:28 AM on September 19, 2011


Whoops, mitheral, you're right: I thought for sure I'd seen separate lighting circuits as a part of the code, and though I can find a lot of sources that recommend it I don't see any code requirement. The reason I'd insist on it is exactly what you mention: I did a quick and dirty wire-up in my garage/shop, and decided to run a light off whatever wires I had handy. Needless to say, I reworked this as soon as I tripped that breaker when only those lights were on. As I fumbled around in the dark I realized how silly it was to save the cost of a breaker and a little bit of wire. Code or not, if you're having electrical work done I recommend making sure your lighting is on a separate circuit.

Also, my copy of Code Check Electrical p.13 says of "3-Wire Edison Circuits" that "Hot conductors must originate from opposite poles", 09 IRC 3501, 11 NEC 100. Which makes that BX off the same side not code.

I am not an electrician, I'm a homeowner. I need to doubly remember that before jumping into electrical threads...
posted by straw at 1:20 PM on September 19, 2011


Most electrical panels alternate poles every breaker or every other breaker depending on the panel as you go down the bus. So even though the wires terminate on the same side it doesn't mean the hots are on opposite poles. In fact pretty it is standard for hots supplying a 240V load or a split circuit to terminate right next to each other. And it is designed this way to accommadate two pole breakers where a single handle controls both poles of a 240V or split circuit. This is why MWBC/3-wire Edison can get people in trouble. In some panels it is easy to change a proper circuit utilizing both pole into a dangerous circuit using only a single pole by simply shifting the breaker one slot up or down.
posted by Mitheral at 3:28 PM on September 19, 2011 [1 favorite]


Response by poster: Mitheral, I bet that's what's up with the 3-wire thing -- the two hot strands of BX terminate right next to each other. I assumed that one half of the box (split vertically) was on one pole and the other was on the other. This is why I'm not an electrician.

The one who came out to the house this morning was friendly and good at explaining things. He definitely set my mind a lot more at ease than it was when I didn't know what was going on with the house. I've got another guy coming tomorrow morning too.

Thanks to you all.
posted by brentajones at 10:43 AM on September 20, 2011


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