EC Magazine doubt

[peter]

In the latest issue of Electrical Contractor magazine, [March 2004, page 29] there is a response by George W, Flach in which he states,
"A 15A, 120V branch circuit can supply (15 x 120) 1,800VA. Since the minimum load permitted in Table 220.3(A) is 3VA per aquare foot, one 15A general purpose branch circuit is allowed to supply a 600 square foot floor area."

I can understand the logic of the first sentence. But my impression is that Article 220 uses the VA per square foot table for service calculations. In other words, it seems that a 15 amp circuit in a dwelling shouldn't necessarily be limited to only 600 square feet or any area measurement. Area has nothing to do with it. Who is right?
~Peter

 

[tom baker]

Re: EC Magazine doubt

I understood it to be you had to install the number of circuits per the ampacity at 15 or 20 amps. The actual area served by each circuit is not specified, just the minimum number required.

 

[a.wayne3@verizon.net]

Re: EC Magazine doubt

The 3VA/sq.ft.sets a minimun required circuits (general purpose)actual installations IE:Lighting, usage has to be considered.IMHO

 

[dereckbc]

Re: EC Magazine doubt

You are still required to add two circuits for the kitchen and one for laundry.

 

[charlie b]

Re: EC Magazine doubt

Originally posted by peter: Since the minimum load PERMITTED in Table 220.3(A) is 3VA per square foot, one 15A general purpose branch circuit is ALLOWED to supply a 600 square foot floor area.

The two words I emphasized from the article you quoted are used in an inappropriate context. The 3 VA/ft2 is intended to ensure that enough power is available to handle the present and future loads. It is only used (as you pointed out) for the service calculation. It is not a design criterion for laying out the branch circuits, for the NEC is not a design manual. If the author of the quote has chosen to use ?600 square foot for a 15 amp circuit? as a ?thumb rule? for his design process, he is welcome to do so. But the author is incorrect, if he is asserting that this is an NEC requirement.

 

[steve66]

Re: EC Magazine doubt

The handbook states:

The scope of Article 220 was previously revised to clearly indicate that the article deals with load computation for branch circuit, feeder and service loads and not with requirements for determining the number of branch circuits needed. The determination for the number of branch circuits is contained in Article 210.


Steve

[ March 31, 2004, 09:12 AM: Message edited by: steve66 ]

 

[william runkle]

Re: EC Magazine doubt

It would be a good rule of thumb for plan of review. Lets say a single family dwelling is at 4800 square feet so you would divide 600va/sq.ft into 4800sq.ft. and get 8-15amp circuits, then a look on the circuit panel drawing to see if matches. Or for the Electrical Contractor to verify the Architect drawing if that is off it should tell him to closely examine everyting else.

 

[russ]

Re: EC Magazine doubt

210.11 requires branch circuits to be installed to supply the loads computed in 220.3. Isn't that saying the same thing the article said.
You would have to have at least one 15 amp circuit for every 600 sq ft.

 

[steve66]

Re: EC Magazine doubt

Russ: I agree that phrase is confusing, but I think it is only saying to limit the load on each branch circuit to that calculated in 220.3. (That would apply more to 220.3(B) than 220.3(A). If you read a little farther:

210.11(B) Where the load is computed on a volt-amperes/square meter or foot basis, the wiring system up to and including the branch circuit panelboard(s) shall be provided to serve not less than the calculated load. This load shall be evenly proportioned among the multioutlet branch circuits within the panelboard(s). Branch circuit overcurrent devices and circuits shall only be required to be installed to serve the connected load).

I think the requirements on the service size are for two reasons: It can be almost impossible to increase the service size at a later time, and there is limited overcurrent protetion on the service. Neither apply to branch circuits, and it is usually realitvly easy to install more branch circuits at a later time.

Steve