Is this true?

[wedgie]

Hello!

I noticed that the electric baseboard wires in my own house were 12/2, but that all the breakers in the electrical box for heating are double-pole 25A. While I don't know much about electricity, I do know that 12/2 wires are meant to be used for 20A circuits.

I posted a question on another forum and some guy said that the Canadian Electrical Code (I'm in Quebec, Canada) allows you to use up to a 30A breaker with #12 wire if the circuit is used exclusively for baseboard heating. He said that back in the day, electric heat wasn't considered a fixed load and you could only load a circuit to 80% of it's capacity, but that this has changed and that I shouldn't be concerned.

I'm asking for a second opinion. Is this true?

Thanks in advance!

[tooltroll]

Yup. I've encountered a similar setup in Manitoba: 20A breakers on #14 wires to hardwired baseboard heaters. Got the same explanation from the inspector here, 5 or 10 years ago. Don't know if it still applies, but probably. . .

[wedgie]

This still sounds a bit weird to me as I always thought #12 wire = 20A max. Here's a copy-paste of the guy's answer to my question where he cites that particular rule for those interested :

From the Canadian Electrical Code: (I assume the NEC is the same)
You can breaker #12 wire with a 30A breaker and a #14 wire with a 20A breaker if the circuit is used only for baseboard heating. Previously electric heat was not considered a fixed load, therefore the circuit could only be loaded to 80% capacity. Now you can use higher rated breakers for #14 and #12 cable only when they supply fixed heating loads. I'm quoting Rule 62-114.8 of the CEC, so don't ask me to explain.

[giddonah]

Technically, you can run 25A on #12. It's just that the NEC restricts #12 to 20A breakers. I've seen quite a few #14 circuits on 20A breakers too. Not that it's right, it's just skirting the boundaries of operation. That's why the NEC restricted #14 and #12, to make it safer.

Heck, if you can cool the cable enough, you can run a LOT of amps on a small wire. Most people just don't happen to be refrigerating their wiring.

[tooltroll]

Hmm. A whole new industry of water cooled wiring? Heh.

Wedgie, just keep in mind that 'minimum code requirement' is just that: a minimum. Not necessarily the best way, but the acceptable way. Personally, I wouldn't skimp on a few bucks for heavier cable: I'd rather know that I'd done the best install, not the cheapest one. However, I doubt you'll want to go to the trouble of ripping your walls open and replacing all your heater cables, so don't worry about it: The CEC says it won't catch fire, so you should be OK.

[wedgie]

Hmm. A whole new industry of water cooled wiring? Heh.

Wedgie, just keep in mind that 'minimum code requirement' is just that: a minimum. Not necessarily the best way, but the acceptable way. Personally, I wouldn't skimp on a few bucks for heavier cable: I'd rather know that I'd done the best install, not the cheapest one. However, I doubt you'll want to go to the trouble of ripping your walls open and replacing all your heater cables, so don't worry about it: The CEC says it won't catch fire, so you should be OK.

What I had in mind was to leave the already existing wiring/circuits that way, but the new heating circuits I'll had (I'm finishing my basement) will use 20A breakers.

Actually I was wondering... Could I just replace the 25A breakers with 20A breakers?? These circuits are for heating only, so maybe I could calculate the amperage of the baseboards on each of these circuits and replace the breakers if the total amperage on the circuit is less than or equal to 20A... If I recall correctly, to calculate how many amps a baseboard uses, I just have to divide the watts by the volts (240V) right??

What do you think?

[tooltroll]

Kudos for wanting to do the basement heaters properly.

Replacing the old breakers? Sounds good if you can get away with it. 20A x 234V (the actual voltage) = 4680W, so if your load is less than that, the 20A breakers should be ok. 25A = 5850W, though, and I suspect your heaters will clock in at over 20A, probably in the 5000W/21.4A nieghborhood. If this is the case, 20A breakers'll just keep tripping, but you're only 'overdriving' the cable by 1½A or so.

[Vector]

Hmm. A whole new industry of water cooled wiring? Heh.

In the July Scientific American there's an article about replacing the national power grid with a system of liquid hydrogen cooled superconducting cables. The idea is that a single pair of cables can carry some huge number of gigawatts at near zero loss, and it acts as a hydrogen pipeline too.

Anyhow, back to our topic.

There are conditions under which smaller wire can be run in a special purpose circuit that would be allowed in a general branch circuit with the same ampacity. This may be one of them. My NEC is buried under a ton of boxes right now.

[ODDJOB]

Isn't hydrogen what's used in the space shuttle's booster rockets?

[giddonah]

the shuttle's booster rockets are solid fuel. They probably have hydrogen in there, but not as H2.

[Vector]

I think the main tank may have liquid Hydrogen in it, but giddonah's right about the boosters.