Master's exam questions, questions.

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throttlebody

Senior Member
Location
Martinsburg, WV
Hi everyone, it has been a while since I have last posted. I let my West Virginia license go null about 5 years ago, thinking I would never need them again. I tested in the mid 90's. I have recently re-examined for my license again. I missed my West Virginia Master's exam by one question, which means I missed a few. My how we can forget things when we no longer apply them daily! However, I do not know which ones I have missed, I only have the score. I would like to better prepare myself by making sure I am understanding the question correctly and finding the answer properly. There are a few calculations that maybe I am reading too far into. Any related help is appreciated.


1) What is the load demand for a mobile home park with 35 sites?

Indexing refers to 550.18, 550 III, and 550.31

550.18 is for calculations based on each site supply cord service feeder.
550.31 is what is needed, I believe.
Demand for 35 sites is calculated on #1 or #2 of 550.31
#2 sq ft is unknown, so I assume that 16000VA is the minimum demand for each lot.
Table 550.31 is the allowance for 35 sites equalling 24% total demand load.

16000VA x 35 x .24DF = 134,400VA total
or
134,400VA/240v= 560Amps total
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2) What is the DC resistance of 420ft of 6AWG cu?


#6 on table 8 has a DC resistance of .491 p/1000ft
We need the resistance of 420ft

R = 420ft x .491ohms/1000ft = 0.20622

or

.491/1000 = 0.000491ohms p/ft x 420ft = 0.20622 ohms


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3) What is the lighting and receptacle demand load for a 2100sq ft dwelling, with 34 complimentary receptacles and 12 lights rated at 100watts each.

220.14 (I) refers to (J) and (K) in which no additional load be added for receptacles of dwelling units or for lights specified in 210.70 (A) and (B).

2100sq ft x 3va = 6300va
3000va x 100% = 3000va
3300va x 35% = 1155va
4155va total demand load.

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4) What is the demand load of a single phase AC 5hp motor @ 230v and 3 - 120v Electric Base Board Heaters @ 3KW?

When figuring demand between AC and Heating equipment, the demand load would go by the largest of the 2? I might be reading too far into this one. They may be asking for a total demand of both together. Also,I am confused as to which formula for the motor to use.

Heat
3 x 1000/240 = 12.5Amps

AC
5hp x 746/230 = 16.2Amps
or
Table 430.248 28FLC Amps x 125% = 35Amps ??
 

throttlebody

Senior Member
Location
Martinsburg, WV
Thank you for your reply. I appreciate your help. It has been stated numerous times for the OP to try to answer the question in the post, before receiving help, I was beginning to wonder if anyone would help, as sometimes it takes a second set of eyes to see what is apparent in the questions. :)

It would appear that they were asking for just what you were suggesting in 220.60 for loads not likely to be utilized at the same time. For some reason, I had kept questioning whether to apply that code or give total demand of both. 220.50 references 430.24, which points to motor and other loads, but other loads would not be used at the same time as they are heating. 440.6 is the Ampacity and rating, but 440.12(A)(2) Equivalent Horsepower: says to use table 430.248 to obtain the LRC. To find branch circuit rating, multiply 125% of the value = 35Amps under 430.24. Heating would be the smallest, so it gets dropped.


Anyone else?
 
Last edited:

Jim Shorts

Member
Location
Central Florida
On #3 you forgot your small appliance and laundry circuits. 220.52(A) & (B), 210.11(C) and 220.14(J).

The answer should be: 5,730 va



2100 x 3 = 6300 va (lighting)
1500 x 3 = 4500 va (small appliance and laundry circuits)

Total load subject to table 220.42 = 10,800 va

10,800 va
- 3000 va @ 100%

7,800 va x 35% = 2730 va

2730 va + 3000 va = 5730 va
 

throttlebody

Senior Member
Location
Martinsburg, WV
GREAT! Thank you for your reply Jim.

The question was written verbatim. Just to clarify what you are saying, if the question asks only for lighting and receptacle demand load, I would still need to include the small appliances and laundry circuits? I am curious because I had another test question that asked verbatim for total lighting, small apps, and laundry demand load. Maybe they are trying to trick me on the question? I really despise trickery in test questions.

My reference to no additional loads for receptacles and lighting were actually my questions to ensure I was reading the question correctly and referencing 220.14(J) correctly. (The extra receptacles and lighting).
 

Jim Shorts

Member
Location
Central Florida
I would definitely add the small appliance and laundry circuits any time that they ask for the total load for receptacle outlets in a home. 210.11(C) states that these circuits must supply the receptacle outlets specified in 210.52(B) and (F). All other general use receptacle outlets of 20 amp rating or less have no additional load calculation required per 220.14(J).
 

pjg

Member
the dwelling unit load should be 10,320 va the way I figure it

6300+4500=10800 the first 10 k at 100% the remaining @ 40% (800x.40=320)

as per 220.82 b 1,2,&3
 

pjg

Member
after further review of 220.10 i'll say it is 6300 va. any part of the atricle after part II is for service load and feeder calculation which allow you to use demand factors. I'm more confused !!
 
Last edited:

Finite10

Senior Member
Location
Great NW
#2 isn't specified as coated or uncoated.
.492 ohms/kFT Uncoated
.51 ohms/kFT Coated = .2142

.00798 ohms difference, or .008 rounded to the thousandths.

Do you recall if the question specified Uncoated or was it verbatim, as in #3?
 

Girl Engineer

Inactive, Email Never Verified
Location
Portland, OR
I failed the first time as well. The test taking tips on this website helped a lot the second time around. Follow those tips and you should have no problem passing this time.
 
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