A marina shore power facility has twenty 20A, 240V receptacles; seventeen 30A, 240V receptacles; and seven 50A, 240V receptacles. After applying deman

[Electricallearner]

A marina shore power facility has twenty 20A, 240V receptacles; seventeen 30A, 240V receptacles; and seven 50A, 240V receptacles. After applying demand factors, the service calculated load for the shore power boxes is _____.

Hi All
I am not sure how I am not getting the right answer -

I have tried all combinations and not getting the correct answer of 630Amps.

I tried (Amps)x(voltage)x(DF) for each type of circuit and then sum it up and devide by 240, and I get 80... LOL
I tried (# of circuits) x(Amps)x(voltage) x(DF) and devide by 240, I get something around 1100

And several other calculations.

Any help? Thank You!!

 

[letgomywago]

You need a book on load calcs. There's specific demand factors for each type of area.

 

[charlie b]

The question is missing important information that would be needed to calculate a real marina. They did not say whether any boat slip is served by two receptacles (i.e, a 20 amp and a 30 amp). If that were the case, then you only need could the higher rated receptacle. Let's assume the 44 receptacles serve 44 separate boat slips.

Another issue with the question is that all 20 amp boat receptacles are fed by 120 volts, not 240.

1. Take 20 receptacles times 20 amps times 240 volts, and write down that result.
2. Take 17 receptacles times 30 amps times 240 volts, and write down that result.
3. Take 7 receptacles times 50 amps times 240 volts, and write down that result.
4. Add the three results.
5. Divide that value by 240 volts.
6. Multiply that value by 50% (the demand factor in table 555.6 for 41 to 50 receptacles).
7. That should give you a final answer of 630 amps.

 

[augie47]

I have to admit I can't come up with 630 but there does seem to be a little trick in the question in that it asks for the demand factor for the shore power boxes and only the 30 amp and 50 amp would be considered shore power per 555.19