Dwelling unit calcs

[creatiger]

I am in the process of preparing for a state master exam and have a question regarding dwelling unit calculations. In the Mike Holt exam prep book (2011) for the dwelling unit standard calculation, there is no mention of adding in the additional 25% for the largest motor. Is this unnecessary if you take into account the following:
1) General lighting and receptacles: sq ft *3, 3000VA small appliance, 1500VA laundry
2) 75% demand factor to nameplate of 4 or more appliances (not cooking, dryers, or ac/heating)
3) Dryer- 5000W or nameplate, whichever is greater
4) Cooking equipment using 220.55
5) AC or heat, whichever is larger


When is it appropriate to add in this additional 25% for the motors? What has me confused is looking at Example D1(b) in Annex D of the code book. I understand what they do in the example, but not when it is appropriate to do this versus the other above referenced way. Thanks

 

[Volta]

Welcome to the forum.

On the list you provided I don't see a motor.

If you are thinking of the one in a clothes dryer or HVAC unit, is is already accounted for.

Granted, I am not loking at D1(b) now, so I may be missing something.

 

[jumper]

I would say there is no need to add in the largest motor, if the largest motor is an continuous load and part of an appliance ( ie: outdoor condenser unit compressor) and you are using the MCA of the unit- the motor/compressor is already factored at 125%. The example may be using a RLA and not an MCA.

 

[cadpoint]

Yes, Welcome to the Forum!

If one would read 210.1 throught 210.3 your answer is really there.

Provided your asking about one or another type of calcuation, your just required to account for the numbers they each are asking for!

I'm am not compairing your OP to the list of each as required, either...

 

[Volta]

Generally speaking, you only need to count 25% of one motor on each level of distribution. Branch, feeder, and the service.
If there are no stand-alone motors (not as part of other utilization equipment), then no adder is needed on that level.

...
If one would read 210.1 throught 210.3 your answer is really there.
...

Not sure exactly where you're going with that. Not much about service calculations there.

 

[cadpoint]

The individual parts or Branchs add up to a service calc. Which process they use will dictate the needed inputs to answer thier question.

Again I didn't go and ckeck their list.

My answer address not only motors for it's circuit service as well as other things, the key I was trying to make that it comes down to a accounting for what's being used with which type of calc. they might use.

 

[Volta]

Ok. Might be more direct though to go right to 220.10, as shown by 220.40, to figure the load on the service.

 

[Little Bill]

I used the MH exam prep. book and looking back at it there weren't any items listed in any of the calculation methods (standard or optional) that required adding 125% for the largest motor. I think they want you to be able to use the items listed and do the calculations from that, either standard or optional whichever they ask you to do for that example.