ECN Forum Forums Code Related Discussion NEC & other Code issues Voltages used for branch circuit calculations

My Thoughts:

The NEC does not tell us "who will specify the voltage."

I will research the original proposal when I get home. I should be able to find that proposal in my library of NEC reports, and the substantiation may include answers to this question.

For now, the test writer is responsible for developing a question like this one, and it has caused many to argue about this issue.

The bottom line:

If you don't use the 115 volts and answer 12, you will be with one wrong answer on an examination.

Joe,
Why is the calculation in my post of 08-03-2003 05:27 PM wrong?
Don

I like Don's computation method. I think it makes more sense than the method everyone including myself used.

I think the question about voltage used is intended more for 60 volt or 90 volt systems not 115 volt systems.

I think the questions on the exam should reflect usual practice not practices that "game" the code.

George, why is 115v a standard voltage in article 430? This is part of the same NFPA (70) document.

Roger

Gentlemen: In addition to Article 430 in Article 440 it says:

What is the determining factor on how many receptacles can be placed on the circuit in question?
Don

Ohms law.

Don, how long can a 20 amp breaker hold 20.35 amps in true design. We know in real life 20 amps is a close number in time curve and duration but in reality a 20 amp OCD is just that, 20 amps.

See table 210.24 "maximum load".

You and I both know what 220.2(A) & (B) says, and we both know the way you are using it is to prove the article wrong and poorly worded. You and I also know the "spirit of the question is to test an exam takers skill and knowledge.

You, yourself have been "troubled" on another forum today with someones claim of being a "master electrician", and with this persons question, it would be in doubt he would have a clue to the answer to this question even if it used 120 v.

My point here is, that if the exam taker had the insight to answer this question with 12, I would feel good about his / her understanding of the determining factors.

Roger

Roger,
The load is the only factor that can be used to answer this question. Per the code 13 duples receptacles on a 115 volt cirucit is a load of 20 amps and is permitted to be protected by a 20 amp overcurrent protective device. How can we say that the calculation has to be made the other way? What code section tells us that? As far as the trip time, the time trip curves for a major brand of breakers show that this load may trip the breaker somewhere between 10 minutes and never.
Don

Don, I can't stand to see a grown man cry. You are right! You are right! You are right!

I know I feel better now.

BTW, let's remember this.


Roger

Roger,
I'm not crying. No one has cited any code section that says the alternate method of calculation that I used is wrong. Until they do, I will insist that 13 duplex receptacles are permitted on a 20 amp 115 volt circuit.

The wording specifing the voltages to be used in the calculations was a result of proposal 2-118 in the 1983 TCR. Even with the substantiation, it is not clear what is meant by the words "unless other voltages are specified". The substantiation said: "There is a need to specify what voltage level the panel instends should be used for branch circuit and feeder calculations. The voltage levels selected are in keeping with the nominal system voltages listed in ANSI Standard C84.1".
The panels comment on proposal 2-208 in the 86 TCR seeking to add the voltages 380Y/220 to the section seems to indicate that I am wrong about who can specify a voltage. The panel rejected the proposal with the comment that: "present wording allows specifing other voltages".
Don