WA admin major calc's

[sparkcity]

Second attempt, got 4 correct. Damn the luck. OK, I need to know where I am going wrong on motor loads in va. The question on the test was for six motors. Three single phase with one motor intermittent 5-minute rated. And three three phase motors with one of them also intermittent 5-minute rated. 460 volt delta with 120/240 transformed at the service. I could not seem to match any of the four choices no matter which way I tried. I used the table 430.148 to get FLC amps for the single phase and table 430.150 to get FLC amps for the three phase motors. The test gives you the motor nameplate values for FLC amps but I learned that nameplate is only used to size overloads so I ignored the nameplate values to determin load. For the intermittent motors I used the demand factors from table 430.22(E), intermittent 5-minute rated, the factor is 85%. Here is how I did the calc's:

single phase;
115v, 2hp=24amps I x E = 2760va
230v, 5hp=28amps(int. 5min) I x E x.85= 5474va
230v, 71/2hp=40amps I x E = 9200va

three phase;
460v, 5hp=7.6amps I x E x 1.732= 6055va
460v, 20hp=27amps(int) I x E x 1.732 x.85= 18285va
460v, 40hp=52amps I x E x 1.25= 51787va

TOTAL VA 93561

Is there a flaw here in my logic? I even dropped out the 1.25 factor on the largest motor and still could not match one of the four answers on the test. Any ideas or help would be great, I would like to pass this thing on the next try. thanks.

 

[CBone]

Re: WA admin major calc's

SPARKCITY I KNOW HOW YOU FEEL.I JUST TOOK THE SAME TEST ON JULY,18 AND PASSED. THIS IS WHAT I DID FOR THAT PROBLEM.I USED THE FLC ON THE FOUR MOTORS THAT DID NOT HAVE THE 5 MINUTE INTERMITTENT DUTY. THEN I USED THE NAME PLATE RATEING ON THE OTHER TWO WITH THE 85%.THE LARGEST MOTOR GETS THE 125% ADDED TO IT.WHEN YOU DO YOUR CALC FOR EACH MOTOR REMEMBER 115v IS NOW 120v,230v is 240v, and 460v is 480v FOR EXAMPLE

480x1.732=831 52AMPS X 831= 43,212 plus 125%=54,015va

120x24=2880va, 240x28=6720va.

I HOPE THIS HELPS YOU ON YOUR NEXT TEST GOOD LUCK

 

[sparkcity]

Re: WA admin major calc's

Thanks Cbone, by the way, did you have the question about the duplex that was to be calculated by the optional method? The question was worded a little funny or should I say fuzzy? I think one of the lowest possible answers was around 500 amps service load. These were 1900 sq. ft. units with the heaters being the biggest loads. Try as I might I could not get anywhere near a 500 amp service load. Did you have that question?

 

[CBone]

Re: WA admin major calc's

SPARKCITY I AM NOT FOR SURE WICTH DUPLEX PROBLEM YOU WERE WORKING ON. I HAD A COUPLE ON MY TEST.SO IF YOU CAN REMEMBER MORE DETAIL TO THE PROBLEM I MAY BE ABLE TO HELP.

 

[charlie b]

Re: WA admin major calc's

CBone: Please turn off the ALL CAPS feature on your keyboard. ALL CAPS makes the text more difficult to read. It is also considered by some to be impolite, as though you were SHOUTING at us. Thanks for your understanding.

 

[sparkcity]

Re: WA admin major calc's

Cbone, to the best of my memory the duplex went something like this;
1900 sq ft
range 10kw
disposal 10amp
dishwasher 11amp
hot water 3kw
heat 2 @ 20kw
a/c 3 @ 17amps/240volt

Part of the question read "use the NEC optional or 2 dwelling method", something to that effect. Can't remember the exact wording. It just didn't say "using the optional method", the question threw in the word "NEC" for some reason. Anyway most of the choices for service load was well around 500 amps. I came up with 277 amps. The above figures may not be exactly what was on the test. The 277 was using the test numbers. I have to congratulate ya on passing this thing. I am planning on retesting next week and hope to be celebrating afterwards. One thing for sure, I will NEVER let this license drop. I think I will renew a year ahead of time.

 

[CBone]

Re: WA admin major calc's

sparkcity here is the answer you are looking for.in the nec 220.33 optional calculation-two dwelling units. read that and you will get your answer.just to let you know that in the six motor problem the 5 minute intermitten duty you will find in table 430.22[e]nec on the top of the page it reads nameplate rating percentages.that would be for the two motors.i hope this helps you.thanks for the congrats, good luck on your test.