single family dwelling question

[295tramp]

Laundry circuit of 1500 va; two small appliance circuits are 3000 va;
1/2 hp,115 volt motor. Balance these loads on a 115/230 single-phase system.
Then answer the following question.

What is the va of the 1/2 hp.115 volt motor?

My answer is 9.8amps x 115 volts=1127 va.

I am getting confused on how to balance the system.
I thought that you try to split up the loads evenly as possible on each phase.
thanks for any help.
RC

 

[charlie b]

I hope this is not a test question, because if so it is a bad question. First of all, the laundry, SA, and general lighting loads get lumped together, and a demand factor is applied, when you calculate the dwelling unit?s total load. So you aren?t really balancing the 1500 with the 3000 and with the 1127 (I agree with that value, by the way). You are balancing the total load on the whole building. You could put all 5627 VA from your question on Phase A, if you wish, as long as the other loads in the house (lights, air conditioning, dishwasher, etc.) are split between Phases A and B in such a way as the total Phase A load is close to the total Phase B load.

Welcome to the forum.

 

[295tramp]

Thanks charlie indeed this was a test question from the simulated exam questions on this site. I don't know if it is trying to trick me into trying something first or just solve the question. thankyou for you help.
RC

 

[gndrod]

BC distribution

BC distribution

Adding to Charlie's reply...a draft of the existing or pre-permit panel schedule will give a visual placement of circuit breakers on the panel bus phase legs.

Panel schedule definition will help plan approximate load distribution of the system by loading equipment and general purpose usage in an overall balanced configuration. (I.e. alternate general purpose bc's to phase legs.)
Another approach to 'balancing' is to use phase-to-phase instead of line-to-neutral loads where possible. I believe this is a simplistic form of energy management. rbj

 

[gndrod]

Thanks charlie indeed this was a test question from the simulated exam questions on this site. I don't know if it is trying to trick me into trying something first or just solve the question. thankyou for you help.
RC

Hi RC,

That was a sincere trick that puzzled me also. The livable structure Sq.Ft. va, SA bc's va, and the laundry va are separate from the motor va unless the standard method calculation total is combined towards a total demand load result.

Your answer is correct on the motor va if the question had linked the NEC 220.53 Load Calculations of the motor as the only load to be derated in the FIP factoring. If there had been four or more appliance FIP's then the motor would have been included in the x75% DF rating of the all the NPR's. I hope my answer is not as confusing as was the question. rbj