GF, in a fairly old mid-1900's house that she's renting. Electrical system has been replaced since the house was built (breakers instead of fuses) but it's still pretty old stuff. House has had some modifications, like the garage being turned into a den and a loft office, and there's been some crazy work done on the electrical panel. House contains some old electric baseboard heaters (on their own circuits) which she is supplanting with some more modern space heaters plugged into AC outlets.

She says that she doesn't understand something about the circuit breakers, and that Google isn't helping her find what she needs to know. So I said I'd ask here. If necessary, I can get photos this weekend.

She says there are some circuit breakers which appear to be two 15-amp small-size breakers next to each other. And they are connected together at the switches so that when one trips they both trip. But they appear to be separate breakers.

My first reaction was that they were actually a larger "ganged" pair to give more amperage. But she says that is not the case, and that her googling says you can't do that anyway (ie, make a 30 out of two 15s). Also, her empirical experience is that they're just a pair of 15's, because she can run one space heater on one of those circuits but not two of them (the space heaters draw about 10-ish amps each).

My question is: Has anyone seen this trick where there are two 15-amp breakers connected together? And what is the purpose for connecting them together? If they are on different circuits, why gang them like that?

I might be able to get photos this weekend.

In my old house we had some circuits like that for the well pump and tumble dryer, in other word the 220V appliances. Someone smarter then I can explain how it works.

Yes, breakers are connected together when each is switching one leg of a 220-240V circuit. Eg. electric oven, hot water heater, electric dryer, or a feed to a sub-panel. All of these are typically 220-240V circuits, and require a breaker on both legs of the circuit. The breakers are physically connected to make it nigh impossible for only "half the circuit" to trip.

The more typical 110-120V circuits each use one leg from a 220-240V source, and use earth ground (from the panel, aka. "neutral") as the other leg. Therefore there is only a single live leg, and only a single breaker is required.

Cheers

That's excellent information, thanks.

Her initial impression was that the circuit in question was a 110 because she plugged a space heater into a regular wall outlet and caused the circuit to trip that way. However, this doesn't rule out that the circuit might have gone to a sub panel she's not seeing, or, was wired in a poor fashion where it SHOULD have gone to a sub panel and didn't.

But this information is great to go on so that we can investigate more. Thanks!

Paired breakers are also used for "split duplex" outlets, commonly found along kitchen countertops here in Canada.

That's where the top and bottom outlets of a standard 2-outlet receptacle are on different circuits, permitting someone to plug in and use both a toaster and a kettle simultaneously.

The breakers are paired, so that when one switches off the electricity at the (breaker) panel to service the outlet, there is no danger of getting electrocuted by either of the two circuits.

In our new house (under construction), I have spec'd 20A split duplex receptacles for the basement workshop area, so that I can use a shop vacuum at the same time as a power tool, plugging both into the same outlet pair.

Normally, 15A capacity would be adequate, but I spec'd 20A due to a pricing anomaly: the builder doesn't charge extra, so.. why not?

Cheers

We also have some ganged light switches where the lights from one switch are on a different circuit than the lights on an adjacent switch. So once again, paired breakers to the rescue, to reduce the electrocution risk when servicing the ganged switches.

Any outlets shared with those lights would then also cause both breakers to trip when circuit capacity is exceeded, even though each outlet is for only a single breaker. This might be the underlying cause of what she observed.

As long as you use the 2.5mm² copper, you should be fine.


You can share outlets with lights on the same circuit in Canada? Interesting. Here it's strictly forbidden, mostly because lights and outlets are on different circuits, using different cross section cables. Lights are on 16A breakers, using 1,5mm² copper cables, outlets are on 20A breakers, using 2,5mm² cables. Remember, it's all 240v here, meaning we get a maximum of 4800 watts out of one circuit. The law says you can put a maximum of 8 outlets on one circuit. Some appliances like my heat pump, my electrical (induction) cooking plate and my steamer are 3-phase (400v). For those I use either 4 or 6mm² copper. (the feed to my house is 3-phase, 32 amps)

In theory you may put a lamp on an outlet circuit (because of the 2,5mm² cable), but not the other way around, but this is never done by any qualified electrician though. ...Well, you could do it if you used 2,5mm² cable for the lights as well I guess, but that just makes that more expensive are more difficult to handle/insert into the switches/lamps because 2,5mm² is a lot more rigid than 1,5mm² is.

Old house? Ha!

We rented an old house and tried to find a breaker to fix an attic fan. We flipped each breaker trying to find the circuit and, even running through them a few times, just frickin' couldn't. The circuit always stayed hot. We figured they missed the circuit on the upgrade and it wasn't protected - yikes!

After asking a couple knowledgeable friends, we started doing them in pairs (very tedious process!) and found the pair.

We called in an electrician to figure out where in the house the cross was. Several hundred dollars later (billed to our rather decent landlord), we traced it to spaghetti in a junction box.

-jk

Yes, and oddly, it is even encouraged. "Mixed loads" they call it. I never did understand that one, but there ya go.

Here, the standard household circuit is 120V, 15Amps, and it is permitted to have a maximum of 12 connected "devices", where a "device" is either a standard duplex wall outlet, or a ceiling light fixture.

There are addtional special requirements for wiring in certain rooms (kitchen, bath, bedroom, outdoors, etc).

Heh. :-P