What is the demand load for one household dryer with a nameplate rating of 4.75 kw

My exam question (based on 2005) was: Calculate the demand load (in VA) of the dryers for and apartment building that has 12 units and 1 public unit (13 meters). The 12 units all have 5kw dryers and the public unit has 2 2kw dryers. Answer: Table 220.54 Demand Factors for Household Electric Clothes Dryers I have a total of 14 dryers so my demand factor is 47-(14-11) which equals 44% (12 dryers X 5000w X 44%)+(2 dryers X 2000w X 44%) = 28160w

What do I do next to convert it to volt amps? 28160 wasn't one of the answers

You sure they do not want amps. Watts to VA is a power factor question not usually found on a test in this format and cannot be answered given this info.

Maybe? I can't remember for sure. I do remember the answers being in the neighborhood of A. 24700 B. 47600 C. 65000

Not exact answers, but that was the basic spread. The question also gave information about all the appliances and such, but I thought it useless info and all I needed was the dryers for the calculation.

was the service 3 phase by chance?

was 32000 one of the answers?

If it is single phase, then is my answer correct?

14 dryers 5 5 4 twice the no. between any 2 phases=10 12x5kw+2x4kw=64kw demand factor t220.54 for 10 dryers, 50% 32000w 220.54 Electric Clothes Dryers ? Dwelling Unit(s). The load for household electric clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served. The use of the demand factors in Table 220.54 shall

be permitted. Where two or more single-phase dryers are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum

number connected between any two phases.

(kW) for loads calculated in this section.

That must be it. To further confirm, the last sentence in the code you provided said that KVA shall be the same is KW in this example. And I do remember the answer being in VA.

Tough question. Thanks for the help :thumbsup:

I think you guys need to re-evaluate your answers. -If I understand it correctly: 1. You have 12 household electric dryers located inside each unit? 2. Then you have two (2) common area dryers?

If I’m correct, then look at your answers again.

I would like to know how you came up with your answers???

Each unit, which is an apartment, has one dryer rated at 5kw. And the public area has 2 dryers rated at 2kw each.

Sorry for not clarifying, I read your post and thought you just moved on

No, I’m here. I guess my question is for jumper.
I have a question for you. You had a multiple chose question with only three answers to choose from? Are you sure of those answers, because it would seem all three are wrong, including the 32Kw or Va.

No, I?m here. I guess my question is for jumper.
I have a question for you. You had a multiple chose question with only three answers to choose from? Are you sure of those answers, because it would seem all three are wrong, including the 32Kw or Va.

Alright, I'm all in. How is 32kVA wrong?

my test had four answers, I can remember the exact numbers other than my answer wasn't one of them.

-The dryer demand factor= 46% [12 dryers-11=1] So: 47-1=46% DF allowed -12 dryers (5Kw min)= 60KW -60kw(.46)=27.6KW Then onsite Laundromat: -2 dryers (5Kw @ 100)=10Kw Note: No demand allowed Ans=37.6kw or 37.6va

Heck, I could be wrong—seeing that I’m rusty

Why are you calculating your demand factor on 12 dryers when there are 14 total?

also there are 12@5kw and 2@2kw

-The dryer demand factor= 46% [12 dryers-11=1] So: 47-1=46% DF allowed -12 dryers (5Kw min)= 60KW -60kw(.46)=27.6KW

Then onsite Laundromat: -2 dryers (5Kw @ 100)=10Kw Note: No demand allowed Ans=37.6kw or 37.6va

Heck, I could be wrong?seeing that I?m rusty

The 12 units all have 5kw dryers and the public unit has 2 2kw dryers.

Why are you calculating your demand factor on 12 dryers when there are 14 total?

also there are 12@5kw and 2@2kw

Good catch jumper!!! :thumbsup:. I have no excuse.

You can only take a demand for the 12. The other two are considered commercial, and no demand allowed for the two dryers located in the shared laundromat...

Interesting twist. I tried finding the code reference that says the commercial units will be at 100% but cant find anything. Where is it? and thanks for commenting

220.54 applies to dryers "in dwelling units. The two dryers in the common area are not "in dwelling units" so the demand factor would not apply to them.

David (and others), what if it is a three phase system? Do you still calculate it based on 12 dryers at 5kw? Which would be 4,4,4 and the two commercial units? as per 220.54 So then I would have 16 dryers at 5kw calculated at 42% = 33.6kw

33.6kw plus the common area which is 4kw = 37.6kw

David (and others), what if it is a three phase system? Do you still calculate it based on 12 dryers at 5kw? Which would be 4,4,4 and the two commercial units? as per 220.54 So then I would have 16 dryers at 5kw calculated at 42% = 33.6kw

33.6kw plus the common area which is 4kw = 37.6kw

36kW plus the common area (4kW) = 40kW demand.

For three phase, you would still use the "twice the maximum connected between any two phases" method described in 220.54. See Example D5(A) in the annex for an example of how to apply that method.

I think you would take 8 dryers (not 16) at 5kW each and apply the demand factor in T220.54. 8*5kW=40kW @ 60% = 24kW. You would then multiply that by 1.5 (or divide the 24kW by 2 phases and multiply be 3 phases - see the example D5(A)) to get 36kW.

36kW plus the common area (4kW) = 40kW demand.

For three phase, you would still use the "twice the maximum connected between any two phases" method described in 220.54. See Example D5(A) in the annex for an example of how to apply that method.

I think you would take 8 dryers (not 16) at 5kW each and apply the demand factor in T220.54. 8*5kW=40kW @ 60% = 24kW...

If it's not sixteen, then in a case with 13 dryers, it would be arranged on phases as 4 4 5, so the max between two phases would be 9. Is that right? So, you don't take twice the max?

If you had 13 dryers, then the max between any two phases would be 5. The demand would be based on 10 dryers.