Example D3

[antenna2001]

I am attempting to solve Example D3 on page 70-719 of the NEC.
I followed the calculations until the part where, to calculate the "Minimum Number of Branch Circuits Required", 8500 VA is multiplied by 1.25. I can't find the code section that requires or permits the 125% factor. If you know where it is, please give me a hand.
Thank you

 

[celtic]

I can't find the code section that requires or permits the 125% factor. If you know where it is, please give me a hand.
Thank you

Read just past where they came up with the 28,400VA....

*In the example, 125% of the actual connected lighting load (8500 VA ? 1.25 = 10,625 VA) is less than 125% of the load from Table 220.12, so the minimum lighting load from Table 220.12 is used in the calculation. Had the actual lighting load been greater than the value calculated from Table 220.12, 125% of the actual connected lighting load would have been used.

 

[antenna2001]

Celtic,
I saw that part. In it they apply the 125% to both, the actual connected load and to the load from Table 220.12 and then they compare both values to choose the largest one.
My question why are they using 125% instead of 100%? I can't find the section that states 125%.
Thanks for the reply

 

[antenna2001]

Rewording the Question

Rewording the Question

I guess I did not state correctly the problem I am trying to solve. Here is a second try:

Why is the lighting load (8500 VA) multiplied by 1.25 instead of just using 8500 VA directly?

I can't find the code section that requires the multiplication.

Can anyone help?

Thanks again

 

[celtic]

I guess I did not state correctly the problem I am trying to solve. Here is a second try:

Why is the lighting load (8500 VA) multiplied by 1.25 instead of just using 8500 VA directly?

I can't find the code section that requires the multiplication.

Can anyone help?

Thanks again

I see what you're saying....still trying to find a "proper" answer.

 

[antenna2001]

I think I found the solution.

I think I found the solution.

210.19(A)(1)

Thanks again for the replies.

 

[Pierre C Belarge]

antenna
The value in example D3 for the actual lighting is 8500VA, and would be multiplied by 125% because it is a continuous load. It is the actual load, not the calculated load.


In my opinion, the calculations in the different examples, and Article 220 are difficult at best to understand. If one is to look at the different calculation expert books available on the market today, one will find many different "expert" methods to find the Many Expert different answers for the same question.
Because what we do is not rocket science, we really only need to be close in our design of systems, hence our services are usually built with a considerable oversizing to account for our lack in proper application of the real math necessary... just ask any electrician in the field to size a service and sit back for a good time.

 

[antenna2001]

I am still in the theoretical world

I am still in the theoretical world

Thanks Pierre,
Yes, I understand that in the real world, the answer would not be this critical. I am, however, preparing for my Colorado's Master Electrician License test, and that is why I need to know how to solve this things. You will probably see me come back for more answers as I try to tackle all the examples in the book.

 

[Pierre C Belarge]

Antenna,

Here is something to think about in regards to test taking.

Not all tests are formatted the same. Sometimes the tests will have calculation type questions that are worth more points, some tests have the calculation type questions valued at the same point value as the rest of the questions (this would be so for most "national testing agency" provided tests).

My suggestion for most type tests is to leave all calculation questions to the end of the test as part of your test taking procedure, especially calc questions that you most likely will spend way too much of a portion of the test, only to get it wrong anyway. GUESS THE ANSWER for those calc questions... you will not waste any time on those questions, and you will save time to find those pesky code questions, probably adding a few points to your test results.

This is what I call "don't sweat the big stuff"

 

[antenna2001]

Testing fear

Testing fear

Pierre,
Thanks for the suggestion. I need every bit of advice. Of course, I am planning to leave the hard questions last. The Master Electrician test in Colorado is mostly calculations. There is no escape from them so I have to keep practicing. Other people have passed so I think there is a very good chance that I will pass it too but I have to work hard to make sure I do. My future employment depends on it.

 

[Pierre C Belarge]

I do not understand why the powers to be focus so much on calculations for the test. We see motor calculation type questions and others. Most electricians do not use calculations on a daily basis for their everyday jobs. Within 6 months to a year they will forget most calc methods they were taught for the test. I say the tests should have some calcs - 1. box fill, 2. pipe fill, 3, conductor sizing, 4 Ohms law and maybe a few others.

There is no "one" test that can prove to a jurisdiction that the person taking the test is fully prepared to be an electrical contractor (the industry is too complex). Just put a fair test together that shows that a person is able to use the NEC to find the answer. This way the person will prepare to be able to use the NEC and take those same skills to the field for future use.