wireday
Senior Member
- Location
- New England
- Occupation
- Master electrician
Have a 240volt 6 space sub panel with a 2 pole 40 amp breaker feeding panel, how many 20 amp breakers can I install? All loads are non continuous, I would like to use four.
IMHO, you can install 6 if you want to. I'm sure you know the rule of thumb is not to load a breaker to more than 80% of its value. That being said, in your case 80% x 40 amps = 32 amps. If you don't estimate the draw to be more than that for any length of time you're OK. Just my opinion.Have a 240volt 6 space sub panel with a 2 pole 40 amp breaker feeding panel, how many 20 amp breakers can I install? All loads are non continuous, I would like to use four.
Thank you gold star, that would be 32 per leg?
Thank you gold star, that would be 32 per leg?
Sorry I wasn't clear in my post but I think Larry gives the best explanation here.:thumbsup:Don't think about "amps 'per leg' ". Think about amps at 120v or amps at 240v. With 120/240v, the more heavily-loaded leg will be the one that matters with a 2p breaker.
You can use as many 1p breakers as you want to. If you overload any one circuit, that breaker will trip. If you heavily load several of those circuits simultaneously, the 40a feeder breaker may trip. It's the total current "per leg" (actually meaning current on either (or both) leg at any given moment) that matters.
That's why the breakers in the main panel can add up to way higher than the main breaker's rating; you're not using many circuits near capacity at any given moment.
Thank you gold star, that would be 32 per leg?
Don't think about "amps 'per leg' ". Think about amps at 120v or amps at 240v. With 120/240v, the more heavily-loaded leg will be the one that matters with a 2p breaker.
You can use as many 1p breakers as you want to. If you overload any one circuit, that breaker will trip. If you heavily load several of those circuits simultaneously, the 40a feeder breaker may trip. It's the total current "per leg" (actually meaning current on either (or both) leg at any given moment) that matters.
That's why the breakers in the main panel can add up to way higher than the main breaker's rating; you're not using many circuits near capacity at any given moment.
Have a 240volt 6 space sub panel with a 2 pole 40 amp breaker feeding panel, how many 20 amp breakers can I install? All loads are non continuous, I would like to use four.
Now let's list more realistic situations in a home. Let's add another breaker for a bedroom for lights and receptacles. Another breaker for bedroom 2 and another breaker for bedroom 3. Let's add your Washing machine and gas powered dryer on another breaker. You maybe just added 1000 watts and occasionally 2500 watts if someone uses a circular saw or space heater or whatever. You are now up to roughly 10 single pole 20A breakers....no problem.
Forget about thinking about amps, think more in terms of watts. Less intimidating (And think VA if you are more advanced)
NEC code actually list outlets at 180 watts or more accurately 180VA.(220.14 (I))
If you hooked up your panel with the loads prescribed, I doubt it would ever trip. If you had a meter tracking it I doubt it would ever go over 4800 watts. Think of it this way too, you would need a whole bunch of people in the house for all these loads to be connected.
I think that you were just trying to make a point about using VA instead of watts but if you're referring to a house there is no 180VA receptacle value.
Fascinating. I see it in section J right after section I in 220.14. As you know, we always use 180 VA in commercial and industrial panels for receptacles...hence the incidental overlap of knowledge if you will. Thanks for the tip.