# NEC Question - OCPD sizing



## DMB5mil (Aug 29, 2008)

I just went through the "NEC Handout" from the "EE PE Materials" documentation provided elsewhere on this board.

Example questions no. 1, 3, 7, 8 ask to calculate loads based on Table 220.12, Section 220.14 and Section 220.43 of the NEC. None of these portions of the code indicate to multiple the VA rating calculated by a 1.25 multipler, yet that is what is done for the solutions to the problems. For example, in problem no. 1, the general lighting load for a 4000 sq. ft. bank is 14000VA (3.5VA per sq. ft) per Table 220.12. However, the answer given is 14000 x 1.25 = 17500VA.

Why do these questions use the 1.25 multiplier for calculating the load in VA? Note, the questions do not ask to calculate the ampacity of the conductors or the OCPD sizes which would use the multiplier.

Please reference code section(s) in your response.

Thanks in advance,

Brian


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## Dark Knight (Aug 29, 2008)

DMB5mil said:


> I just went through the "NEC Handout" from the "EE PE Materials" documentation provided elsewhere on this board.
> Example questions no. 1, 3, 7, 8 ask to calculate loads based on Table 220.12, Section 220.14 and Section 220.43 of the NEC. None of these portions of the code indicate to multiple the VA rating calculated by a 1.25 multipler, yet that is what is done for the solutions to the problems. For example, in problem no. 1, the general lighting load for a 4000 sq. ft. bank is 14000VA (3.5VA per sq. ft) per Table 220.12. However, the answer given is 14000 x 1.25 = 17500VA.
> 
> Why do these questions use the 1.25 multiplier for calculating the load in VA? Note, the questions do not ask to calculate the ampacity of the conductors or the OCPD sizes which would use the multiplier.
> ...


I am not sure and did not take my time reading your posts but the 1.25 factor is usually applied when the load is considered to be continous.


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## DMB5mil (Aug 29, 2008)

The 1.25 multiplier is used when loads are continous, but I can't find where this assumption is assumed in Section 220. Perhaps it is one of those overarching assumptions that are difficult to find in code, but is taken for granted???

Thanks.


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## jdd18vm (Aug 29, 2008)

DMB5mil said:


> I just went through the "NEC Handout" from the "EE PE Materials" documentation provided elsewhere on this board.
> Example questions no. 1, 3, 7, 8 ask to calculate loads based on Table 220.12, Section 220.14 and Section 220.43 of the NEC. None of these portions of the code indicate to multiple the VA rating calculated by a 1.25 multipler, yet that is what is done for the solutions to the problems. For example, in problem no. 1, the general lighting load for a 4000 sq. ft. bank is 14000VA (3.5VA per sq. ft) per Table 220.12. However, the answer given is 14000 x 1.25 = 17500VA.
> 
> Why do these questions use the 1.25 multiplier for calculating the load in VA? Note, the questions do not ask to calculate the ampacity of the conductors or the OCPD sizes which would use the multiplier.
> ...


I don't have the Handout you mentioned, and couldn't locate it here in a quick glance. But I'll take a shot. Dark and DMB are right. Section 220 tells you what values you need to use for a given application (general lighting per building type, receptacle, show window, electric dryer etc). Calculate the total loads you have, applying any demand factors in 220.

You are then going to select Ampacity of conductor for either a *Branch Circuit* (Article 210.19 (A) 1.), *Feeder* (Article 215.2 (A) 1. or *Service* 230.42 (A) these all have what youre looking for. Stating basically minimum size/capacity shall be based on "Non continuous loads plus 125% of the Continuous loads".

Continuous being more than 3 hrs (Article 100 Definitions).

Hope that helps, let me know if not.

John


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