calculation question

[Rpmccready]

Why is it that when you do a optional calculation you come up with a smaller size service and conductors than standard?

 

[jumper]

Basically, it seems that according to the links below it is because the optional is less steps and more loads get to be subject to demand factors.

I have never really looked into why, but the optional seems to be smaller in most cases.

http://ecmweb.com/code-basics/clearing-multi-family-dwelling-unit-calculations

http://iaeimagazine.org/magazine/20...calculations-in-the-national-electrical-code/

 

[Carultch]

Basically, it seems that according to the links below it is because the optional is less steps and more loads get to be subject to demand factors.

I have never really looked into why, but the optional seems to be smaller in most cases.

http://ecmweb.com/code-basics/clearing-multi-family-dwelling-unit-calculations

http://iaeimagazine.org/magazine/20...calculations-in-the-national-electrical-code/

So in the event that one uses the optional method to "add up" loads, do they even need to think about the standard method?
If the optional method commonly results in lower service sizes, it seems like the standard method would be an unnecessary calculation that is more complex and is unlikely to be of any value to do it.

 

[jumper]

So in the event that one uses the optional method to "add up" loads, do they even need to think about the standard method?
If the optional method commonly results in lower service sizes, it seems like the standard method would be an unnecessary calculation that is more complex and is unlikely to be of any value to do it.

There are certain conditions that have to be met in order to use the optional method. While most dwellings do meet them, not all do. It spells it out in the links.

 

[GoldDigger]

Both the standard and the optional calculations turn out to seriously overestimate the demand in just about any real life situation.
One method overestimates more under some conditions than the other, so the code writers give you the choice of using the one that gives the smaller load number IF you meet the necessary conditions.
You can always apply the standard method, you can often apply the Optional method.
In real life it is a good idea to do both if you are not sure what kind of environment you are working with or think it may be different from a typical usage and then use the smaller number.