questions about demand factors for dwelling units

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KEM

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Caldwell, Idaho, USA
When given the square footage of a residence and that there is a bathroom and laundry circuit being the only information given, it seems to me that the only code requires that 3000VA be included in the calculations. But what else? If a particular load is not specified, it seems to me that indicates electrical power provisions for such appliances don't need to be included in the calculations for reasons that the appliances may be gas. It seems to me that gas appliance power needs and the bathroom circuits are included in the general lighting calculation of 3va /sq feet according to my understanding of the NEC. To calculate electrical appliance loads like a range, oven, dryer, window air conditioner, electric furnace, the nameplate rating is required. Therefore, if the square footage of this residence if 1000 sq feet, garage not included, would have a general lighting load of 3000, 1500 for the washer, and 3000 for the two require kitchen small appliance circuits. The total demand factor would be 3000 at 100%, and the remaining 4500 at 35% or 1575 va for a total demand factor of 4575 va. Please correct me if I am wrong.
 
You are correct for as far as you have taken it. But there may be more to do. For example, the dryer rule says to include at least 5000 VA "for each dryer served." So what happens if you don't know whether the dryer will be gas or electric? What happens if you don't even know whether there will be a dryer at all? My answer is that you have to include the 5000 VA unless you have certain knowledge that there is to be no electric dryer.

The same goes for the electric range. The loads that we need to include for cooking equipment are based on knowing the ratings of the equipment. But what if we know nothing? My answer is that you assign 8000 VA, per column C of Table 220.55.

And what about heating and air conditioning? In my area, almost none of the single family dwelling units have air conditioning, but they all have heat.

I believe the purpose of article 220 is to ensure that we provide enough capacity to allow the homeowner to function. The NEC will not tell us that, of course. So if you are looking for the bare minimum code requirement, you might have found it.

Welcome to the forum.

 
It sounds to me like it's time for an RFI, because you haven't been given enough information to properly do your job.

If you can't get any more information, then I think Charlie's got the right idea -- you have to assume electric appliances. Given the range of temperatures in Caldwell (winter lows in the teens and single digits, summer highs in the 90s and sometimes breaking 100), I can't imagine a home being without heat and A/C. The heat may or may not be electric, but the A/C will be.
 
If you do not put in a range receptacle (high current) you can be pretty confident that only a gas dryer will be used.
If the drawings include a dryer outlet, you have to assume it will be electric.

Tapatalk!
 
What to assume and not in dwelling demand factor calculations

What to assume and not in dwelling demand factor calculations

If it was up to me to decide what to include in demand factors, I'd agree to figure in possibilities. In real cases, you would have the customer to interrogate to obtain all pertinent info or a customer submitted plan to refer to. However, I just recently took my Master Electrical License test base on the 2008 code and in those tests, it seems to me if it is not specified, don't figure it in. Only include what the code requires such as two small appliance kitchen circuits is required. A garage is not figured into the general lighting load calculation per square feet of dwelling space. A laundry load means 1500 kw for a washer outlet. I reviewed the code and confirmed bathrooms circuits are not required to be a circuit by themselves from what I could find.

These kind of questions drive a compulsive/obsessive tendency wild.

I failed one more question allowed for being qualified to request and pay for a review of the test and so I have no way of knowing which questions I passed or failed. So I am opening up myself to getting feedback on questions I struggled a bit with and hopefully, if I am wrong, find out if I need to re-calibrate my thinking.

Thanks for your responses.:ashamed:
 
Ah. Didn't realize it was a test question, as that does change things quite a bit. In that case, I would say that you're right; you should just go with the Code minimum. But I don't have any first-hand experience with Electrician licensing tests, and the PE didn't have any of this type of question when I took it. Hopefully you'll get some licensed sparkies to chime in with their experience.
 
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