HELP!!!

[marsbar42]

I am taking the master's practice exam in the Tom Henry 2005 Calculations: Exam Questions and Answers, test 1. Question #3 is...What is the minimum demand on the service for 300 duplex receptacles in a hospital?...a)20.8kva b)27kva c)32kva d)54kva. The answer they give is a)20.8kva. They get this answer by using table 220.42. 180va x 300= 54000kva. 50000@ 40% and 4000@ 20%. I do not understand why table 220.42(Lighting load demand factor) was used instead of 220.44(Demand factors for non-dwelling receptacle loads). I am taking my Wisconsin Masters and I need to understand why this is done. I also have a question about question 13...How many #8 RHH conductors w/o outer covering can be installed in a 1 1/2ENT. I came up with 13.9, so I put the answer as 13. They have the answer as 14. I thought that 13.9 was the maximum so you had to go down. Am I not right?

[ January 28, 2006, 06:25 PM: Message edited by: marsbar42 ]

 

[peter]

Re: HELP!!!

The NEC does not precisely conform to our physical universe. Note 7 in Chapter 9 statrs that the decimal fraction .8 shall be rounded up. Usually, the human, scientific and accounting communities will use .5 as the deciding point. But the NEC has its own mathematical constants.
Where else is the circular area of a cable diameter squared?
What is the volume of a 2 X 3 X 2 box?

I can't help you with the first part of your question, but even publishers get some things wrong.
~Peter

 

[marsbar42]

Re: HELP!!!

I understand that normally you would round up, but when you're talking about conduit fill, you cannot excede the maximum. 13.9 wires would have to be rounded down because 14 would excede the maximun fill. Am I looking at this wrong?

 

[peter]

Re: HELP!!!

Read Note 7 to Table 1 in Chapter 9:
"the next higher whole number shall be used to determine the maximum number of conductors permitted when the calculation results in a decimal of 0.8 or larger."
Usually the Code would use the term "may" instead of "shall" but, in this sityation, they are maybe trying to keep the test makers honest. In the field, wire fill is how many wires you can stuff into the conduit.
It doesn't really matter though since derating will limit you to about 10 wires. Except I get 20 + ground for #14 @ 12amps in 3/4" EMT.
~Peter