Post exam debrief - couple more load calc questions

[electrofelon]

So I took my Major load calcs portion of my Washington administrators on sat and got all 10 questions correct, but two of the questions I was a little unsure on and the numbers didnt match perfectly.

The first question asked to calculate using the alternative method the service load for a residential duplex. Now 220.82 applies to one dwelling unit and 220.84 applies to three or more, so what is the correct way to calc this? Only thing I could think of was to use 220.82 for each unit and add them together, was that likely the intended solution or did I miss something?

The other one was a bear, an industrial/commerical building with two occupants each having a whole bunch of stuff, calculate the service load. Okay so I dont remember the exact loads and even if I did I think I agreed to not release, discuss, share any details of the questions..but to see if I was on the right track and just made a minor math error, some questions:

1. For calculating the service, I can essentially lump all the stuff in both units together right? How many units there are doesnt really effect any demand factors or anything other than each one needs 1200VA for a sign, correct?

2. There were a bunch of motors. I take the 125% of the largest one using table 430.24x and add the 430.24x value of all the other ones, correct?

3. Heat was larger than AC so I just use 100% of the heat Nameplates, correct? If Ac was larger than heat do I use 100% or 125% of the AC nameplate?

4. I did 2 VA per square foot for gen lighting, 100% demand.

5. Each of the two units had a large fridge and a microwave. I add the nameplate of those four together and get to use 80% demand from 220.56.

I think thats it, there was some show window and a bunch of receptacle outlets but I dont think i could have screwed that up. I used the demand factors 220.44 for non dwelling unit receptacles.

Thanks

 

[sparky08]

Hey, I think I got the same test through PSI a couple of weeks ago. Unfortunetly, I got 6 out of the 10. I blasted through the WAC and Theory though. I"ve been studying the load calcs. for about a month ahnd when I ran across those 2 or 3 questions about Duplex's, I crapped. I hadn't had 1 question with duplex's out of the 4 Mock Exam books I had. I did some research and found I was missing 220.85 out of my NEC Handbook!! What did you come up with for the Industrial 2 tenant building? How did you do it? Add "everything" together and apply the Factors? Sorry, I don't remember the details if it was standard or optional method. Forgive me, I've never done this Forum thing before.

 

[electrofelon]

Hey sparky,

Yeah thats what I got my first try, 6 out of 10. The alternative method duplex question threw me a bit because I cant figure out what section covers it. What is 220.85? My 2008 handbook has 220.84 and then 220.86. I was also a bit shaky on the industrial/commercial question hence why I asked all the questions about it, but I think its not as bad as it looks, just unclear about a few details. If I have it right, really the only demand factors you get to use in an example like that are for the receptacle outlets and the kitchen equip - Mine also had a few welders and the welders article has some demand factors too though. So then its just knowing whether to use 100% or 125% for continuous/noncontinuous loads and motors. I get confused on that still a bit. On my test, my numbers were a bit higher than one of the answers so I chose that one assuming I had left out a demand which I think it was the kitchen eqiup I did not demand.