220.5 b

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mattc

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hello

this question comes from the 2008 exam preparation book from mike holt page 254

the question is how many 15 amp circuits can be put on a 2000 sq ft home
2000x3va=6000va 6000/120=50amps

50amps/15amp circuits=3.3

220.5 (B) says that I can drop it to 3 circuits because the fraction is less then .5

but the right answer is 4

so what am I missing

thanks
matt
 
mattc said:
the question is how many 15 amp circuits can be put on a 2000 sq ft home
2000x3va=6000va 6000/120=50amps

so what am I missing

thanks
matt
Click to expand...

I know what you're trying to say, but just in case, you can put as many 15A circuits you want, but there is a minimum. 220.5 (b) is regarding fractions of amperes, and in your case you're dealing with a fraction of a circuit, so you need to round it up.
 
CFL said:
. . . .you can put as many 15A circuits you want. . . .
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I agree. This is a badly worded question. There ought to be a qualification program that a person must pass, before being allowed to write test questions.
 
charlie b said:
I agree. This is a badly worded question. There ought to be a qualification program that a person must pass, before being allowed to write test questions.
Click to expand...

I would fail. It was an amazing realization to me as to how difficult it is to write a "good" question. For many years I attempted to prepare questions for a local IAEI quiz. To word the questions where there is only one truly qualified answer is a difficut job, especially when dealing with the NEC.
 
I might be able to pass such a certification process. But I have taken a class in technical writing, so that gives me an advantage. :roll: The hardest part of being an author in a technical environment is divorcing yourself from the words you just wrote, and trying to look at them as though you had never seen them before, and trying to determine if they make sense.

Hey, maybe I should create an artificial need for training and certification of people who write electrical tests. If I could get it accepted as the industry standard, I'd be rich. I would need a name to call the group who complete the course, and pay my fee :)grin:). How about this: the International Network of Electrical Professional Testers. :D
 
charlie b said:
I might be able to pass such a certification process. But I have taken a class in technical writing, so that gives me an advantage. :roll: The hardest part of being an author in a technical environment is divorcing yourself from the words you just wrote, and trying to look at them as though you had never seen them before, and trying to determine if they make sense.

Hey, maybe I should create an artificial need for training and certification of people who write electrical tests. If I could get it accepted as the industry standard, I'd be rich. I would need a name to call the group who complete the course, and pay my fee :)grin:). How about this: the International Network of Electrical Professional Testers. :D
Click to expand...

I'm all for it. I can probably be grandfathered in as I can find any number of electricians who will certify my qualification as I.N.E.P.T.:grin:
 
CFL said:
I know what you're trying to say, but just in case, you can put as many 15A circuits you want, but there is a minimum. 220.5 (b) is regarding fractions of amperes, and in your case you're dealing with a fraction of a circuit, so you need to round it up.
Click to expand...


Thanks
but It does not say that .

220.5 (B)
where calculation result in a fraction of a ampere that is less then .5 such fractions shall be dropped.

It say calculation and this is a calculation right from this article
3VA from table 220.12

I am not saying that I don't think you are right because I do but you can see what it says and there is not exception to this rule.

matt
 
this is not a calculation involving fractions of amperes.

this is a calculation involving the number of circuits it will take.

the answer is a minimum of 4, because you cannot wire a fraction of a circuit, and 3 ckts is not enough.
 
mattc said:
Thanks
but It does not say that .

220.5 (B)
where calculation result in a fraction of a ampere that is less then .5 such fractions shall be dropped.


matt
Click to expand...


The actual wording is SHALL BE PERMITTED TO BE DROPPED.

This is permissive language, not mandatory language. See 90.5(B).


As has been explained, the number you have come across would require going up to the next higher amount for the number of circuits. It is better to learn on a test or exam book than to make that mistake in the field. So, you have accomplished part of your goal by studying, you should feel good, not bad.
 
augie47 said:
I would fail. It was an amazing realization to me as to how difficult it is to write a "good" question. For many years I attempted to prepare questions for a local IAEI quiz. To word the questions where there is only one truly qualified answer is a difficut job, especially when dealing with the NEC.
Click to expand...

Part of the success of writing a question where there is one truly qualified answer it to realize, there may be more than one truly qualified answer.
So, choose just one of them for A, B, C or D.

The saving grace of multiple choice tests for the writer, is in the instructions. "please choose the most correct answer" is usually part of the instructions.
That really makes a lot of test takers really mad.


Charlie
I have tried to join the INEPT group of writers...I didn't qualify. ;):D
 
mattc said:
Thanks
but It does not say that .

220.5 (B)
where calculation result in a fraction of a ampere that is less then .5 such fractions shall be dropped.

It say calculation and this is a calculation right from this article
3VA from table 220.12

I am not saying that I don't think you are right because I do but you can see what it says and there is not exception to this rule.

matt
Click to expand...

The fraction is dropped at the end of the calculation,when calculating a house load you may have several fractions but you dont do anything until you are complete.You were not calculating amperage but calculating for min circuits so you would not drop the fraction
 
(50A)/(15A per circuit) does not equal 3.3A rounded to 3A

(50A)/(15A per circuit) = 3.3 circuits (minimum required) therefore rounded up to 4 circuits

Follow your labels in fractions.
 
I think the problem here is that 220.5(B) is for calculation purposes and not for figuring the answer to this question. Let's look at it simply. Theoretically a 15 amp cir will handle 1800 watts. If we use 3 cir. then we have used 4800 watts. The problem is we still have to cover 6000 watts (2000 sq. ft. x 3) and we only have cover 4800 watts with the 3 circuits, thus we need another circuit to cover the remainder.
Hope this helps.
 
You are rounding down, which has already been described as OK for amps and NOT OK for circuits.
 
CFL said:
. . . you can put as many 15A circuits you want, but there is a minimum.
Click to expand...
Well, no there isn't. ;) I don't have a copy of Mike's exam book, so I can't tell if the question has been quoted accurately. But you can legally wire a house without a single 15 amp circuit. :)
 
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