Load Center Calculation: Bathroom 20 Amp

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ESolar

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Eureka, CA Humboldt County
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Electrician/Contractor
Where and how do bathroom 20 amps circuits figure into sizing a panel/load center?
In this case there is a new subpanel going on a 50 amp circuit for cooktop, oven, and lighting. It occurred to us that the owner would benefit from upgrading the adjacent bathroom counters at 20 amp at the same time. But I am not sure how to calculate the demand in determining if the 50 amp subpanel can take it.
 
Technically you're supposed to take 3 VA times the square feet served by the outlets, and add that to whatever you already have.

I'd be more worried if 50A is enough for the oven and cooktop together. Probably its fine but I'd wanna see the specs.
 
jaggedben said:
Technically you're supposed to take 3 VA times the square feet served by the outlets, and add that to whatever you already have.

I'd be more worried if 50A is enough for the oven and cooktop together. Probably its fine but I'd wanna see the specs.
Click to expand...
•Ampacity of cooktop + oven = 43.3 amps (see below)
•Kitchen Lighting circuit = 225 sqft x (3VA/sqft)/240 = 3 amps
•Vent hood = 2 amps (name plate rating)
•Bathroom circuit = 50 sqft x (3VA/sqft)/240 = 0.625 amps
TOTAL = 49 amps

"Range" calculation
•11KW cooktop
•7.3 KW oven
•combined name plate rating (CNPR) = 18.3 KW
•12 KW < CNPR < 27 KW
•Max Demand = = [1.0 + 0.05 x (18KW- 12KW)/1KW] x 8KW = 10.4KW= [1.0 + 0.05 x (18KW- 12KW)/1KW] x 8KW = 10.4KW
•Ampacity of max demand = 10.4/240 = 43.3 amps (50 amp circuit OK)
•FYI the maximum CNPR for the existing 50 amp circuit is 22KW: [1.0 + 0.5 x (22KW - 12KW)/1KW] x 8KW/240 V = 50 Amp
 
petersonra said:
Cutting it close. I did not know anyone made a 50 amp panel board. I would be seeing what it would take to go to a larger feeder and pb.
Click to expand...
In this kitchen the lights were on the SA circuits and the owner wants a vent hood. The approach, to reduce costs, is to use the existing 50 amp range circuit (and 50 amp breaker) to feed to a panel (rated at 100 amps but fed with that 50) thereby avoiding running new lighting, bathroom, and vent hood circuits. I will also wire the cooktop on a 30 amp with 6 AWG to future proof it for the possibility of a range (which are typically 40 amps). The panel will have: 30 (cooktop), 20 (oven), 15 (hood), 15 (lights), 20 (bath).
 
petersonra said:
Cutting it close. I did not know anyone made a 50 amp panel board. I would be seeing what it would take to go to a larger feeder and pb.
Click to expand...
On the cutting it close: The lights, although computed at 3 amps, are more like 0.5 amps (7 recessed LED cans, with normally 5 on, and an under cabinet led strip). The computed demand with that adjustment is 46.5 amps. To max this out:
With the oven on a cleaning cycle, all burners at max on the cooktop, and the lights on,
its possible that either a hair dryer and/or the hood might trip the 50 breaker. But Such a scenario is highly unlikely. That is why NEC has developed the adjustments for the demand.

This kitchen also has the standard 2 x 20 amp small appliance, 20 amp micro, and 20 amp GD/DW. The fridge is on a SA circuit. One note: The SAs are multiwire. I find that when a multiwire lands in a 2 gang box for DW/GD and SA with a GFI, that the box fill is often exceeded or maxed and that it's very difficult to get those 12s pushed in there. I went with a 3 gang and tossed in a dead front GFI for the DW/GD. That way the GFIs are both accessible and there is no GFI hiding under the sink.
 
With all of that said: Does anyone see an issue with this plan? Note that there are many articles stating that a kitchen needs a dedicated 50 amp range circuit. I cannot find that in the NEC (e.g., what if there is a gas range - why would I need a 50 amp circuit?). Is that requirement in the NEC? If not, it seems that that is simply considered good practice - and I agree. This design means that the 50 amp feed is being used for a number of circuits (although the cooktop and oven are on dedicated circuits fromthe subpanel). I was actually surprised by how much I could theoretically fit on that 50 amps (assuming that my calcs are correct of course) and I wonder why, for minor upgrades in kitchen electrical where new runs are difficult and costly, that the 50 amp isn't the go to solution.
 
It wouldn't surprise me if the 50A range requirement is in a lot of energy codes or local ammendments, especially in jurisdictions pushing electrification. But I agree it's not in the NEC. NFPA avoids that sort of thing for the most part.
 
The requirement for a 50A plug for a range would be to give the homeowner the option of going electric even if they had a gas range to begin with.
 
Also I'm not really familiar with 220.55 but I don't follow your complicated calculation above. Don't you simply use the 11kW from column C in this case? 11,000W/240V = 45.8A
 
jaggedben said:
Also I'm not really familiar with 220.55 but I don't follow your complicated calculation above. Don't you simply use the 11kW from column C in this case? 11,000W/240V = 45.8A
Click to expand...
No. It's treated as one combined appliance. So it gets the 8KW (column C) + 5% for every KW greater than 12KW (18KW - 12KW = 6 KW; 6 x 0.05 x 8KW = 2.4KW). It can be written more simply as: 8KW + 6 x 0.05 x 8KW = 10.4KW
 
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