CB counts for gen lts/rec in dwelling unit panels

[malachi constant]

In dwelling units NEC requires 3VA/sf for general lighting & receptacles. What is the minimum number of 15A breakers that are required to serve "general areas"? I was once told the rule of thumb was one 15A for every 500 sf. At the time I checked the math and it made sense to me. But now going through the math again...

15A breaker * 0.8 = 12A (derating for 15A circuit breaker)
12A * 120V = 1440VA (VA allowed to load on one 15A breaker)
1440VA / 3VA/sf = 480sf (sf allowed to be "loaded" onto one 15A breaker)

So it seems the rule of thumb should be one 15A circuit for every 480 sf - using 500sf is a hair too liberal a number. Am I correct?

Again I'm talking MINIMUMS here. Not "best practices". I wish that were not the case but gotta keep the clients happy.

Well, KIND OF wish it wasn't the case - staying tight to the code is a little exhilerating WHOOOO

 

[suemarkp]

You don't have to limit the receptacle load to 80% in a dwelling, as general use circuits aren't a continuous load. So its 1800VA per 15A circuit, divided by 3 VA per square foot. This gives you 600 square feet for 15A circuit or 800 sq ft per 20A circuit.

Make sure you round up when you count how many circuits you need (e.g. 2.1 circuits would have to be 3). So 500 sq ft per 15A circuit is probably a good estimating value.

 

[Jim W in Tampa]

You could go as high as 600 feet but i really would not suggest it. That could easily be 4 bedrooms 12 x 12 and that is less than 4 amps each.

 

[George Stolz]

Again I'm talking MINIMUMS here. Not "best practices". I wish that were not the case but gotta keep the clients happy.

What is the objective of the exercise? If you're trying to determine the number of breakers to purchase, then going by square footage is using a shotgun as a sniper rifle.

 

[jwjrw]

What is the objective of the exercise? If you're trying to determine the number of breakers to purchase, then going by square footage is using a shotgun as a sniper rifle.

I love shotguns and sniper rifles!

 

[malachi constant]

Thanks all. I'll go with 500 sf as a simple and conservative-ish rule of thumb.

What is the objective of the exercise? If you're trying to determine the number of breakers to purchase, then going by square footage is using a shotgun as a sniper rifle.

I used to specify general breakers as seemed logical - one for every one or two bedrooms, etc. A few years ago had one owner & their contractor request bare minimum required. The owner said they are willing to deal with any tenant complaints about capacity/tripping.

Owner requests it, they understand the implications, and it meets code, who am I to say no?

 

[ceb58]

You could put every thing except laundry, bath and 2 sabc on 1 15 amp breaker.

 

[jwelectric]

You could put every thing except laundry, bath and 2 sabc on 1 15 amp breaker.

Only if the dwelling unit is 600 square feet or less