Help with a calculation!!!!!!!!!!!

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fletcher

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Detroit Michigan
I am taking a class at the community college for my own info. I am not an apprentice.

One of the problems my instructor gave me is the following.

"Apply 75% Demand Factor, 220.17 if Four or More "Fastened-in Place" Appliances. If Less than Four, Figure at 100%. Do not include electric ranges, clothes dryers,space heating, or air conditioning equipment.
Line 11 13,072 x 0.75 = 9804 VA"

Then we use a form that says:

Water heater = _______ VA
Dishwasher: = _______ VA
ect....

I don't even understand the question, please help!!!!!!!!!!!
 
Re: Help with a calculation!!!!!!!!!!!

The question comes from a "service load calculation," as described in Article 220 of the National Electrical Code. If you want to bring power to a new building, then you have to figure out how many things inside the building will need power. That article gives you a step-by-step process for performing the calculation.

You are being asked about one aspect of the calculation process. This particular step involves appliances, usually in the kitchen or the utility room. It is a safe bet that a homeowner will not be running the dishwasher, the garbage disposal, and the trash compactor, all at the same time that the water heater will be heating water. The NEC does not require you to provide enough power to run all of them at the same time. This permits you to have a smaller service load, and to save the homeowner some money.

The rule in question is that you take all of the appliance load, and add them up, using units of "VA." For these types of machines, the unit of "watts" is essentially the same. The rule tells you that if you have four or more such appliances (not counting the ones you listed), then instead of counting all of their VA you only need to count 75% of their total VA. When you get that number, you add it in with the other numbers that come from the other steps in the process.

By the way, this does not often help in a single family home. But consider an apartment building. Every unit will have a dishwasher and a water heater. When you are calculating the service to the entire building, you get to use the 75% factor for the total number of appliances in all the apartments. It really helps save money in this type of situation.
 
Re: Help with a calculation!!!!!!!!!!!

Does anyone know of a good load calculator available on the Internet? I've used some great ones for voltage drop and was just wondering if someone could recommend one for load calcs.
 
Re: Help with a calculation!!!!!!!!!!!

Celtic,

Thanks for the quick response. I shold have looked right under my nose before posting!
 
Re: Help with a calculation!!!!!!!!!!!

I made a quickee version for load calculations based on some of that xls file...now if I could just remember where I stored it...LOL
 
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