I'm new to the trade. When laying out a circuit in a one-family home. 2203(B)(9) says 180w per outlet. Am I wright in thinking I can put as many as I want as long as I dont go over the 3w per sq. foot ie. 100 outlets on 15a circuit per 480sq. foot. And what about light load? fixture are not bought at rough in and exact load not known. what do you older and wiser ones do
circuit load
- Thread starter wyatt
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: circuit load
When you perform a service calculation for a house (or any other facility), the idea is to make sure there is at least enough power to handle the customer?s needs. It?s ok to have more power than the calculation shows is needed, but not ok to have less.
You are confusing the ?watts per square foot? part of the calculation with the design of branch circuits. You need to allow the owner a minimum of 3 watts per square foot to cover lights and certain other loads as described in Article 220. The conventional method of designing a branch circuit is to convert the 180 VA per receptacle, at 120 volts, to 1.5 amps per receptacle. That would mean you should not go over 10 receptacles on a 15 amp circuit. However, there is also a rule that says a branch circuit should not be loaded over 80%. This would limit a 15 amp branch circuit to a 12 amp load, or to a maximum of 8 receptacles.
Does this give you at least a start of an answer to your question?
When you perform a service calculation for a house (or any other facility), the idea is to make sure there is at least enough power to handle the customer?s needs. It?s ok to have more power than the calculation shows is needed, but not ok to have less.
You are confusing the ?watts per square foot? part of the calculation with the design of branch circuits. You need to allow the owner a minimum of 3 watts per square foot to cover lights and certain other loads as described in Article 220. The conventional method of designing a branch circuit is to convert the 180 VA per receptacle, at 120 volts, to 1.5 amps per receptacle. That would mean you should not go over 10 receptacles on a 15 amp circuit. However, there is also a rule that says a branch circuit should not be loaded over 80%. This would limit a 15 amp branch circuit to a 12 amp load, or to a maximum of 8 receptacles.
Does this give you at least a start of an answer to your question?
charlie
Senior Member
- Location
- Indianapolis
Re: circuit load
Charlie, I normally agree with you but I think you are off base on this one. I had a customer one time that wanted receptacles every six feet instead of 12 feet. Should I have put in twice as many circuits? These were in the family room, living room and bedrooms. Just because he wanted about twice as many receptacles didn't mean he had twice as much load.
I don't do this any more since I quit the EC business a 1/4 century ago.
Charlie, I normally agree with you but I think you are off base on this one. I had a customer one time that wanted receptacles every six feet instead of 12 feet. Should I have put in twice as many circuits? These were in the family room, living room and bedrooms. Just because he wanted about twice as many receptacles didn't mean he had twice as much load.
I don't do this any more since I quit the EC business a 1/4 century ago.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: circuit load
Just to add to what both Charlie's have said,
I think one over looked place in the home where circuits get over loaded the most is in the kitchen.
with that said I would like to add that here is a list of circuits that I install there.
15 amp for kitchen/dinning lites unless there is a lot of cans or tracks
20 amp for dishwasher/disposal
20 amp range/refrigerator
20 amp dinning room general purpose receptacles
20 amp dinette general purpose receptacles.
no less than 2 20 amp circuits for counter space.
and if I get ice makers, compactors large Sub Zero refrigerators then these too will be on a dedicated circuits.
A note on counter space receptacles is if I have a lot of receptacles then I will not put more than three receptacles on a circuit.
Keep in mind code is just a minimum and the last thing you want is breakers tripping on the home owner.
Just to add to what both Charlie's have said,
I think one over looked place in the home where circuits get over loaded the most is in the kitchen.
with that said I would like to add that here is a list of circuits that I install there.
15 amp for kitchen/dinning lites unless there is a lot of cans or tracks
20 amp for dishwasher/disposal
20 amp range/refrigerator
20 amp dinning room general purpose receptacles
20 amp dinette general purpose receptacles.
no less than 2 20 amp circuits for counter space.
and if I get ice makers, compactors large Sub Zero refrigerators then these too will be on a dedicated circuits.
A note on counter space receptacles is if I have a lot of receptacles then I will not put more than three receptacles on a circuit.
Keep in mind code is just a minimum and the last thing you want is breakers tripping on the home owner.
Re: circuit load
I've read elsewhere the code (who could read it all)does not specify (for residences)# of receptacles per circuits, however, our inspectors generally follow the 180 watt rule, which is not a bad idea, for new construction. On old work, you're eliminating an extension cord, and additions to the 8 or 10/11 are OK.
I've read elsewhere the code (who could read it all)does not specify (for residences)# of receptacles per circuits, however, our inspectors generally follow the 180 watt rule, which is not a bad idea, for new construction. On old work, you're eliminating an extension cord, and additions to the 8 or 10/11 are OK.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: circuit load
To ?The Other Charlie?:
I tend to be careful and precise in the selection of my written words. But sometimes the meaning does not come out as clear to the reader as I had intended. When I said, ?The conventional method of designing a branch circuit. . . ,? my intended meaning was that (1) This is not a code requirement, (2) More often than not, it is calculated this way, so that the number of receptacles per circuit is limited in this fashion, (3) It can be done other ways, and (4) It?s a design choice. With this clarification, am I still ?off base?? Am I missing something else?
To ?The Other Charlie?:
I tend to be careful and precise in the selection of my written words. But sometimes the meaning does not come out as clear to the reader as I had intended. When I said, ?The conventional method of designing a branch circuit. . . ,? my intended meaning was that (1) This is not a code requirement, (2) More often than not, it is calculated this way, so that the number of receptacles per circuit is limited in this fashion, (3) It can be done other ways, and (4) It?s a design choice. With this clarification, am I still ?off base?? Am I missing something else?
charlie
Senior Member
- Location
- Indianapolis
Re: circuit load
Sorry Charlie (I love to say that), you are right on. I didn't understand your answer.
Sorry Charlie (I love to say that), you are right on. I didn't understand your answer.
Re: circuit load
I don't want you to think that I want to milk out a load for all that it is worth but, laying out a bed room with 7 or 8 outlets and a fan light why can't I catch a hall outlet and nearby bath lights. this to me is low load area. this all came out when we went to afci $20+ per breaker. one bed on 2 circuits that cost. Not to mention that one room with 2-3 breakers is hard to work on(up and down the stairs 3 times)
I don't want you to think that I want to milk out a load for all that it is worth but, laying out a bed room with 7 or 8 outlets and a fan light why can't I catch a hall outlet and nearby bath lights. this to me is low load area. this all came out when we went to afci $20+ per breaker. one bed on 2 circuits that cost. Not to mention that one room with 2-3 breakers is hard to work on(up and down the stairs 3 times)
pierre
Senior Member
- Location
- Westchester County, New York
Re: circuit load
220.3(B)(10) Dwelling Occupancies.
This is where you will find that there are no restrictions as to the number of receptacle outlets per branch circuit for dwelling units. You are permitted in dwellings to put as many as you like. As far as being practical, that is another story.
Pierre
220.3(B)(10) Dwelling Occupancies.
This is where you will find that there are no restrictions as to the number of receptacle outlets per branch circuit for dwelling units. You are permitted in dwellings to put as many as you like. As far as being practical, that is another story.
Pierre
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