Calc Help

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highlakeselectric

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bend or
Additional equipment is being installed in an existing industrial plant. Addition will require a new 480 volt sub distribution panel to feed these loads none of panels rated 100%


a) 480/277 lighting panel supplying 535 KW florescent lights

b) 2-250 hp 480 volt 3 phase air compressors


c) 480/208y/120 3 phase transformer which supplies

5- 10 hp 208 3 phase pump motors

3- 25 hp 208 3 phase vacuum pump motors

17- 20 amp 120 volt punch press receptacles

8-30 amp 120 volt volt drill press receptacles

1-36 amp 208 volt 3 phase hot press

250- general purpose receptacles


1) minimum size overcurrent for feeder to lighting panel?
700, 600, 1000, 800

2) minimum rating in amps for air compressor disconnect?
378, 347, 242, 302

3) Excluding exemptions using THWN-2 copper wire which of the following meets minimum code requiremnets for a feeder supplying the lighting panel? (base answer on 1 conductor per phase in parallel conduits)

3 parallel 300 kcmill

3 parallel 500 kcmill

3 parallel 750 kc mill

3 parallel 800 kcmill


4) Minimum size transformer necessary to supply 208/120 volt loads
150 kva, 225 kva, 300 kva, 500 kva


5) Minimum bonding jumper in THWN? Phase conductors are 3 parallel THWN copper per phase in separate conduits
4/0, 3/0, 250 kcmill, 2/0

6) Minimum code requirement for the primary feed to transformer? THWN conductors, phase conductors are 2 parallel THWN copper per phase in single conduit.
2- 4/0, 2- 3/0, 2- 700 kcmill, 2-1000 kcmill



this is as far as i can get:

535 kw. 535x1000=535,000 va
535\831.36=643.52 amps
643.52x1.25=804 so 1000 amp?
or.. 643.52 amp= 700 amp overcurrent to lighting panel 125% for continuous lighting?

Any help would be great


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Smart $

Smart $

Esteemed Member
Location
Ohio
Ummm... how about just showing us your VA for each list item and your math from there.

We're not going to do it for you and then take a multiple choice quiz. :happyno:
 
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highlakeselectric

Member
Location
bend or
Here it goes , im not a pro so be easy on me ;)


Answer 1:
535, 535x1000=535,000 va 535,000/831.36=643.52 amps 643.52x125=804 so 1000? For continuous lighting? Or 643.52= 700 amp overcurrent to lighting panel

Loads for air compressor


2-250hp 480 v 3 phase

302 amps x 831.36 = 251.070.72 x 2 = 502,141.44


502,141/831.36 = 604 amps (not one of the answers)??? It asks for minimum in amps for air compressor disconnect

480|208|120

HOT | NEUTRAL

5 -10 HP 3 Phase- pump motors:

5x30.8 a x 360.256=55479 55479 | 0

3-25hp 208 3 phase vacuum pump motors

3x74.8x360.256= 80841 80841 | 0

17-20amp120 punch press rec

17x20x120=40800 40800 | 40800

8-30amp 120 volt drill press rec 8x30x120= 28800 28800 | 28800

1-36amp 208 volt 3 phase hot press

36x360.256= 12969 12969 | 0

250 gen purpose recepts 250x180= 45000 45000 | 45000 ____________________________ 252,189 | 114,600

HOTS 252,189/360.256=700.02 700 amps

NEUTRAL 114,600/360.256=318.10 318amps


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highlakeselectric

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Location
bend or
Im not sure hot to derate the recetacles to get any of the answers as well as how to calculate other portions of this i took a class and my instructor isnt helping unfortunately. Oregon does not calculate these like any book i guess. Can anyone get any of the answers i cannot no matter how i reduce or apply demand factors. Thank you for any help !!!!!


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Smart $

Smart $

Esteemed Member
Location
Ohio
Better, but still have a ways to go to make it understandable and easy to review.

Before we go there, This is an addition to an existing building?

Existing capable of supplying intended new load or planning something else?

You plan on running one feeder or multiple (or a new service) or panel(s) and compressor disconnects fed separately?

The reason I ask the above is because you appear to have lighting panel, compressor disconnects, and 208/120 all separate, yet your OP ask only about sizing one parallel feeder for lighting panel... so it appears you are mixing the load calc's for three, four, who knows how many different feeders. Something has to distribute power to these loads and you are not giving us a clear picture.
 
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highlakeselectric

Member
Location
bend or
I am studying to take a test for the state of oregon and this is the type of info they give you it does not state any more than this. Thats my problem it kimd of a guessing game what there asking this would be exactly like the last half of the test basically. I assumed there basically asking as if there 3 seperate feeders to a b c loads im assuming .


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Smart $

Smart $

Esteemed Member
Location
Ohio
highlakeselectric said:
I am studying to take a test for the state of oregon and this is the type of info they give you it does not state any more than this. Thats my problem it kimd of a guessing game what there asking this would be exactly like the last half of the test basically. I assumed there basically asking as if there 3 seperate feeders to a b c loads im assuming .
Click to expand...

highlakeselectric said:
I take it as the questions actually dictate how the loads are calulated.
Click to expand...
Okay.

1) I'd say lighting panel OCPD at 1000A because the 125% continuous load factoring.

2) The disconnects for the compressors would/should be individual. This would be motor FLC times 125% typically for minimum.

3) Not certain what they mean by exemptions for THWN-2, but I suppose they are just saying to use regular THWN. The lighting panel requires at least 1000A feeder per 240.4(C).

4,5,6) Answers depend on accurate 208/120 load calc. I didn't see any 220.44 demand factoring...
 
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highlakeselectric

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Location
bend or
Thanks ill keep working out the other portions and see what i get . That definitely answers the ac discos question . After im of of work ill try to figure out how to derate those recepts and see what i come up with its a guessing game if the puch press and drill press can be added to receptacle loads 220.44 since they have a specific amperage . I would think 220.44 only applies to the 250 gen purp. Recepts 250x180 = 45000 then apply derate , dont you think? Thanks again for your input!


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Smart $

Smart $

Esteemed Member
Location
Ohio
Agree with only GP recepts applicable 220.44. Press recepts are likely individual circuits calc'd under 220.14(A) or (C)

If this were an actual calc', I'd question the amps for press recepts. True the circuit would have to be rated for the recepts, but the load calc only takes actual motor load into account.

Also, don't forget the extra 25% for largest motor... :D
 
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highlakeselectric

Member
Location
bend or
But its asking the overcurrent for feeder for lighting panel . Which will be 480/277 i thought it would have to be rated of the largest voltage in panel ?


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lauraj

Senior Member
Location
Portland, Oregon
Question #3: Wire Size using 75C column of 310.15(B)(16) because of temperature limitations from 110.14(C)(1)

300 kcmil x 3 = 285A x 3 = 855A
500 kcmil x 3 = 380A x 3 = 1140A <------- winner
750 kcmil x 3 = 475A x 3 = 1425A
800 kcmil x 3 = 490A x 3 = 1470A
 
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lauraj

Senior Member
Location
Portland, Oregon
highlakeselectric said:
But its asking the overcurrent for feeder for lighting panel . Which will be 480/277 i thought it would have to be rated of the largest voltage in panel ?


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Click to expand...

Nope, the amps are just based off of the power equation for the actual load: I = P / E. Since the voltage of our load is 277V we have to use that to calculate the current.

No different than using 120V for the receptacle loads.
 
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