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blowmax10 09-29-2007 12:57 AM

Rated load question
I'm converting my attic into a bedroom and about to ad a 20 amp breaker to my box using 12/2 wire

The question that i can't find the answer to is how much is ok to put on this new circuit

right now I'm planning to put - 2 light fixtures (both with one bulb that i will be using the 13 watt fluorescent bulbs in) and 3 to 4 outlets

the outlets won't be used for anything major (typical bedroom stuff)

is this ok or is it too much??

if some one could give me the rated watts of a 15 amp and a 20 amp circuit that would be great

thanks :)

Andy in ATL 09-29-2007 04:44 AM

The short answer is the twentyA circuit is plenty. In commercial applications the code tells us that you allow 180VA(watts) per receptacle. Using Ohms Law: I=P/E allows us 13 receptacles for 20A circuit. In a dwelling unit it falls under general lighting loads at 3VA per sq./ft. But..... thats only for calculating the service. There are no restrictions(In the USA, Canada is different!) on the number of outlets on a circuit. All that being said, ytou are in good shape with what you have and could actually downsize it to 14/2 and 15A breaker:)

Edit to add: Using Ohm's Law p=e*i 20A=2400W 15A=1800W

fw2007 09-29-2007 08:15 AM

My opinion only:

I would put the lighting on a different circuit than the receptacles, or split the receptacles and lighting between two circuits, regardless of the branch size.
The reason for my thinking is that if the breaker trips, you don't want to throw the entire room out.

That said, it would be a total waste to bring up a second branch just for this purpose. Perhaps you could use an existing circuit already available in the attic for the lighting.


J. V. 09-29-2007 10:11 AM

I like to keep lighting and receptacles seperate, but in this situation one 20 amp circuit would be fine. You could use 15 amp, but why? You have to run the wire anyway. Use 12/2 and 20 amp breaker. No limit on recepts either.

I like the idea of using an existing lighting circuit for upstairs if possible.
Its nice to have lights when installing the

Don't concern yourself with watts. You can add up the lamp watts, but you can't determin watts on recepts without knowing what your plugging in.

Andy in ATL 09-29-2007 10:39 AM

Don't concern yourself with watts. You can add up the lamp watts, but you can't determin watts on recepts without knowing what your plugging in.[/quote]

Nor should you worry about it! Even though you are the homeowner you are also the new head electrician on this job!:yes: The fact is, on any given circuit you can plug in 15 hairdryers and force the breaker to trip. :whistling2: As far as seperating lights and receptacles, that is up to the head electrician (you). If I had extra money I would consider running 15A for my lights and 20A for the recps. That being said, as a real "head electrician" if it was my house i'd run 15A and call it good.:wink:

Stubbie 09-29-2007 11:41 AM

Well...... I think you are only asking how much will your 20 amp breaker support. So I think you have already decided on 20 amps. As it sounds like you have already bought the wire and breaker. I see you have already been given the wattage total for 20 amps. Recommended that you only load it to a maximum of 16 amps or 1920 watts.


There is a product that is available that makes running circuits in finished homes a tad bit easier. In that you can run one cable and get 2 circuits out of it. This is called 2/2 G romex or nm-b. It allows you to only pull one cable in your home run and has 2 neutrals and 2 hots and ground. It beats the heck out trying to get 2 cables pulled through difficult runs to other areas of finished homes. It also solves the problem of MWBC shared neutrals especially if you are going to be required by local code to have afci protection for the bedroom lighting and receptacle outlets and you want 2 circuits. This would be my choice if I was doing this project.

Also I would not put the required lights for your stairwell on the same circuit with the bedroom another reason to have that second circuit available to you don't have to arc fault it. This saves you about 40 bucks between the cost of an afci and regular inverse time breaker.. Or you can tap for your 3-way lighting circuit for the stairs off another existing circuit and cap off the other circuit in the 2/2 G in your homerun box and cap the other end at the breaker panel. It is now in place to be used another day. Only thing additional is I would run a piece of cable matching what you use in the bedroom circuit from the home run box to an accessible area and put the end in a junction box and cap it at both ends. This will make it easily usable for future needs. You will only need to add a breaker in the panel and connect at the homerun box and you have yourself a new circuit.

It looks like this.....

Just my thoughts.


Andy in ATL 09-29-2007 03:19 PM

Stubbie, why only 16A? I didn't really think anything in a house was considered continous load.

Stubbie 09-29-2007 03:40 PM


There is no requirement for 16 amps on the total circuit. I see where I was rather confusing in my sentence structure . What I was trying (not so good) to say was that you should not plug anything into one outlet that is over 16 amps. I agree... I did a poor job of using my own words to explain NEC 210.21(b)(2).
Sorry Andy.... sometimes I get to typing away and I make a goof now and again. Good catch though just the same.


blowmax10 09-29-2007 06:47 PM

Thanks guys this has been a lot of help

and the reason that i don't split up the lights and the outlets is because the wiring in this old house is a mess - the north side of the room is already powered by one circuit and the south side by another

i wish i could just redo the hole room but there are parts that i couldn't get to unless i ripped everything out

again thanks to everybody who responded its a big help :thumbsup:

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