Load calculation

[Chris O'Connor]

When I asked a few weeks ago, I was a bit confused but now I have done more research and done my own load calculation. Here it is: would one of you more experienced souls check this to see that I have done it correclty. I'm sure the math is fine, I mean the assumptions and method.

Questions: The main area I am still questioning is about the number of circuits considered to be applicance circuits that are subject to the 1500VA rating rather than just being general lighting circuits subject to 3VA/SF (should I have included the garage ckt). Also in adding an additional general lighting circuit, I do not need to increase the load requirement. Right? My last question is about the dishwasher. Code says it needs to be seperate from disposal but can it be part of ckt 7 or do I need a dedicated 20A new branch ckt.

Calculations follow:

Existing 100A service CKT Amps Location Load

1 15A Exterior and Interior lighting l1 lamps on 6 switches 2 50A/240V Range 1 hard wired box 3 30A/240V Drier 1 receptacle 4 20A All bedrooms and bathrooms 11 Receptacles, 3 switches 5 20A Living Room, Middle BR 5 Receptacle, 1 ceiling fix, 2 switches 6 20A Refrigerator, microwave, sink 3 receptacles 7 20A Kitchen counter, wall, 2 receptacles 8 20A Garage, attic fan, patio 4 receptacles, 1 switch 9 20A Disposal 1 receptacle , 1 switch 10 20A Back Yard Receptacle and Shed 3 receptacles, 2 lamps, 1 switch (GFCI)

NEC 220-31 Calculation of Loads Service = 100A x 240V = 24000VA (Main) Other Loads

1000 SF x 3VA/SF = 3000VA (Ckt. 1, 4, 5, 10) Appliance Ckt 3x1500VA = 4500VA (Ckt. 6, 7, 8) Range = 8000VA (Ckt. 2) Dryer = 5000VA (Ckt. 3) Disposal = 1000VA (Ckt. 9) subtotal = 21500VA

First 8000VA at 100% = 8000VA Remainder at 40% (13500VA) = 5400VA

Total loads = 13400VA /240V = 55A

New Loads Dishwasher = 1200VA (Ckt. 7) Lighting Circuit = included (Ckt. 11) Steam Generator = 8500VA (Ckt. 12) New Loads = 11200VA

• Original loads (21500VA) = 32700VA

First 8000VA at 100% = 8000VA Remainder at 40% (24700VA) = 9880VA

Total loads = 17880VA /240V = 75A

[SQLit]

Dishwashers have always been on seperate circuits per the NEC. However some jurisdictions made exceptions to the rule. Better check with your local jurisdiction on what they are enforcing.

Every kitchen must be served by "at least two applicance circuits" pretty close to a quote from the book. If you have a built in microwave, add a circuit. If your microwave is counter mounted it is a good idea (not required) to have a seperate circuit for it. Microwaves can be fussy about gfci protection.

Additional lighting circuit would be added to the calculation. At least I would. Since it is not going to make you change the service. Some would argue that it is included with the 3 va for general loads.

Your calculations and methodology looks good to me.

calculations snipped--------------------------------

[Doug Miller]

Oh, really? Got a Code cite for that?

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[m Ransley]

An older frige and high power microwave together could be an issue, mine used to blow when comming on at the same time, Newer friges are

50-75% more efficient and most newer microwaves are smaller. What is a steam generator.

Was your heating system and AC included.

3 bedrooms and a bath on 20a, only you know about what will be used But I would blow 20a.

Garage, attic fan and patio . A big fan, lights on, and the door opening may or may not be and issue. None of your ratings seem to acount for any surge load. But then again only you know your eqipment.

[John B]

If a dishwasher should have its own circuit, would you make that a GFCI circuit? I would think not, as the appliance is hard-wired and dedicated. Yet there are indications that any "receptacle" within 6 feet of a kitchen faucet needs to be GFCI-protected. I never heard that a dishwasher needs its own circuit. I am quite certain mine does not. What would the rationale for that be? I doubt my dishwasher draws 10 Amps. I am looking at the booklet that came with my dishwasher, three years ago. It's a GE Profile PDW7800. There is no mention of its amerage draw. The instructions say that the power circuit must be protected by either a 15A or 20A breaker. A separate circuit requirement is not mentioned. I could picture putting a hard-wired microwave oven on the same branch with a dishwasher. One would expect that they would not be operated simultaneously. That never happens in my home. Does the NEC allow two appliances to share a circuit breaker, when the breaker would pop if both appliances ran simultaneously, but common sense would indicate that the two appliances would normally not be used simultaneously?

"SQLit" wrote

[Chris O'Connor]

heat is gas with fan only, no AC and a steam generator is used to make a steam room in the bath. Micro and fridge on same ckt is fine but add a toaster oven and it blows the fuse every time. Seems like a lot for one ckt to me but it was built that way and seems to work fine. Most lights are CCFL by now so lighting load is low.