master exam need help

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threeelectric

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beckley, wv
q1. what is service size of 14x28 mobile home general lighting and small appliance?

q2. what is load demand of 155,000ft2 school?

q3. same school with 35x45 room how many lights if 1 light covers 65ft2?

q4. 3 electric clothes dryers 4kw ?

q5. 3 electric ranges 6kw 4kw 4kw?

q6. if output is 255 watts and is 88% efficient what is input?

q7. what is t3b? had a code question about it cant remember but was unable to find anything on it a fuse???

cant remember anymore details of the questions wrote down all i could thanks
 
roger

roger

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Along with your answers, explain how you came to them and if you are wrong we can point you in the right direction.

Roger
 
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threeelectric

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Location
beckley, wv
question 1 my first answer was 16.40 amps

after reading the question it asked only for general lighting and small appliance
550.18(c) optional method for lighting and appliance load 220.82 shall be permitted

220.82 b 100% of first 10 kva plus 40% of remainder loads
14x28x3=1176 va
small appliance 2x1500 va = 3000 va
laundry 1500 va

total 5676va
5676va less than 10kva so its at 100%
5676va /240v 23.65 amps

230.79(c) says sfd min service size is 100a
230.79(D) says all others min 60a

my guess would be 100 amp


am i to far off to be helped lol ive been studying lots of diff material brain feels like it cant accept anymore info

also i had all these worked out to my ability but cant find them? these questions were on my test last month
so ill try and work them out again
thanks for any help
 
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threeelectric

Member
Location
beckley, wv
question 6
if output is 255 watts is 88% efficient what is input?

255 / 0.88 = 289.772 watts input

my test im allowed nec, key word index, and uglys book could not find this formula anywhere during test is this just something everyone else knows?

found half of the formula on page 15 of uglys at bottom
 
Smart $

Smart $

Esteemed Member
Location
Ohio
threeelectric said:
question 1 my first answer was 16.40 amps

after reading the question it asked only for general lighting and small appliance
550.18(c) optional method for lighting and appliance load 220.82 shall be permitted

220.82 b 100% of first 10 kva plus 40% of remainder loads
14x28x3=1176 va
small appliance 2x1500 va = 3000 va
laundry 1500 va

total 5676va
5676va less than 10kva so its at 100%
5676va /240v 23.65 amps

230.79(c) says sfd min service size is 100a
230.79(D) says all others min 60a

my guess would be 100 amp


am i to far off to be helped lol ive been studying lots of diff material brain feels like it cant accept anymore info

also i had all these worked out to my ability but cant find them? these questions were on my test last month
so ill try and work them out again
thanks for any help
Click to expand...
550.32(C) Rating. Mobile home service equipment shall be rated at
not less than 100 amperes at 120/240 volts, and provisions
shall be made for connecting a mobile home feeder assembly
by a permanent wiring method. Power outlets used as mobile
home service equipment shall also be permitted to contain
receptacles rated up to 50 amperes with appropriate overcurrent
protection. Fifty-ampere receptacles shall conform to the
configuration shown in Figure 550.10(C).
Informational Note: Complete details of the 50-ampere plug
and receptacle configuration can be found in ANSI/NEMA
WD 6-1989, National Electrical Manufacturers Association,
Standard for Wiring Devices ? Dimensional Requirements,
Figure 14-50.
 
charlie b

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
My problem with question 2 is that they don?t give you enough information. If all they want is the lighting load, then you can get that from Table 220.12, and take note that the demand factor provided in Table 220.42 is 100% for a school. But that leaves out receptacles, HVAC, plumbing equipment (e.g., circ. water pumps), and cooking equipment (presuming the school has a cafeteria). There is an optional process for schools, but you need to know about all the installed loads in order to use it. So I would call this a badly worded question.

Question 3 is a trivial exercise in arithmetic.

For Question 4, take a look at Table 220.54.

For Question 5, take a look at Table 220.55. This table is a bit tricky, so read it carefully.

I have no idea what t3b would mean.

Welcome to the forum.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
threeelectric said:
Does table 220.86 have a factor in the school school load question?
Click to expand...
There's not enough info to answer using standard or optional method. With the optional method, Table 220.86 requires you to use the connected load to determine load per area, and the connected load is not given.
 
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fmtjfw

Senior Member
Location
Fairmont, WV, USA
Smart $ said:
There's not enough info to answer using standard or optional method. With the optional method, Table 220.86 requires you to use the connected load to determine load per area, and the connected load is not given.
Click to expand...

If they only give you the sq. ft., then I'd answer with what I could calculate from the Sq. Ft.
 
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