(206) 949-5683, Top Rated Plumber, Seattle

1. ## Electrical subpanel for new addition

I need to wire a new 2nd floor addition. Since I'll have several circuits on the second floor and the (200amp) main panel is in the basement, I'm planning to have a sub-panel on the 2nd floor feed the new circuits. I'm wondering if the following plan makes sense?

Here are the stats:

- 3 bedrooms
- 2 baths (one new one the second floor plus a remodeled bath on the main floor -- I plan to use one dedicated circuit for both baths)
- 1 laundry in second floor bath
- small balcony to include lighting and outlet
- 854 total sq ft (including the main floor bathroom)

For circuits I'm thinking:

- 1 15-amp lighting circuit
- 1 (or 2?) 20-amp circuit(s) for bedroom/office outlets w/AFCI breaker(s)
- 1 20-amp dedicated laundry circuit
- 1 30-amp dryer circuit
- 1 20-amp bathroom circuit (serving 2nd floor & main floor baths)

From a DIY book worksheet, I calculated that I'll need a 60amp breaker, fed via a #6-3 copper cable. Here are the details from the worksheet:

Basic Light/Receptacle Load (854sq ft x 3w): 2562w
Laundry circuit: 1500w
Dryer: 6240w
Outdoor (1 receptacle x 180w): 180w
Gross load: 10482w (total of above)
NEC safety adjustment (10482 x 1.25): 13102.5w
Convert to amps: (13102.5 / 230): 56.97amps (= total load)

Does all of the above make sense?

Thanks.

2. No sense at all.

Square footage time 3 watts per square feet plus 1500 for laundry plus nameplate on dryer and calculation is over. No need for the 125% or the 180 VA for the outside receptacle.

The conductors supplying would depend on the type of conductors and how installed but #6 copper NM cable is only good for 55 amps

3. Well, I guess that response was somewhat helpful.

So:

>>"Square footage time 3 watts per square feet plus 1500 for laundry plus nameplate on dryer and calculation is over."

Is there a better rule of thumb here?

>>"No need for the 125% or the 180 VA for the outside receptacle."

Removing those from the calculation results in a 44amp load.

So, a 50amp panel fed by 6-3 cable?

Thanks.

4. When doing a residential calculation it is 3 watts per square foot and no additional continuous load or the need of 180 watts per device.

When doing a commercial calculation then the 180 per device and 125% for continuous loads is required.

5. Ok, I missed your original point about the dryer. So, based on that and your most recent post, would that mean the total load is just 11amps (2562 / 230)? Or do I need to add some load for the dryer, just not the full 6240?

Thanks.

6. I got 42.925 amps for the panel that will be supplying those circuits in the original post.

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