NEC 210.20 (A) clarification.

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Location
Ford Motor Company
Occupation
Industrial Electrician
Hello. This is my first time posting to this forum. As I was reading through 2020 NEC 210.20 (A) today, I am not sure if I'm overthinking something or not. The part of this Article that I'm having trouble with is the latter half "...the rating of the overcurrent protection device shall not be less than the noncontinuous load plus 125 percent of the continuous load." With almost 40 years in the trade, every time I saw this stated in the Code this way, I automatically would size the OCPD for 125%. But what I'm reading - clarify this please - is (paraphrasing) "...shall not be less than the noncontinuous load (100% of whatever this value may be) PLUS 125 percent of the continuous load (125% of whatever this value may be). Simple math - 100% of 1 + 125% of 1 = 2.25% I know there are other Code Sections where this type of wording is also used. Am I missing something or is this wording misleading me, and does it need to be changed? Your advice and opinions are appreciated. Thank You.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
All load noncontinuous = 100% * 1 + 125% * 0 = 100%
All load continuous = 100% * 0 + 125% * 1 = 125%
Half the load continuous = 100% * 0.5 + 125% * 0.5 = 112.5%
Etc.

Cheers, Wayne
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I don't have a 2020 Code but that appears to be the same wording as the 2014 & 2017.
I'm not clear which part of that is bothering you.
Your background being industrial, you may not be accustomed to sizing conductors (210.19) and OCP (210.20) at 100% of the non-continuous load but it is allowed by Code keeping in mind the Code is a "minimum standard" an often uncommon term in industrial settings.
 

kwired

Electron manager
Location
NE Nebraska
Hello. This is my first time posting to this forum. As I was reading through 2020 NEC 210.20 (A) today, I am not sure if I'm overthinking something or not. The part of this Article that I'm having trouble with is the latter half "...the rating of the overcurrent protection device shall not be less than the noncontinuous load plus 125 percent of the continuous load." With almost 40 years in the trade, every time I saw this stated in the Code this way, I automatically would size the OCPD for 125%. But what I'm reading - clarify this please - is (paraphrasing) "...shall not be less than the noncontinuous load (100% of whatever this value may be) PLUS 125 percent of the continuous load (125% of whatever this value may be). Simple math - 100% of 1 + 125% of 1 = 2.25% I know there are other Code Sections where this type of wording is also used. Am I missing something or is this wording misleading me, and does it need to be changed? Your advice and opinions are appreciated. Thank You.
If you have equal amount of continuous and non continuous load then your result of 225% would be correct.

Often times you have all continuous or all non continuous load and therefore the other part is zero times 1.0 or 1.25.

If you have 10 amps continuous and 5 amps non continuous your result is (10 x 1.25)plus (5 x 1.0) = 17.5.

If you have 10 amps continuous and zero non continuous your result is (10 x 1.25) plus (0 x 1.0) = 12.5
 

kwired

Electron manager
Location
NE Nebraska
225% of that "equal amount", which is only half of the total load. So 112.5% of the total load.

Cheers, Wayne
Well I think it comes down to OP overthinking it like he said.

What he wrote can be taken as:

100 amp continuous
500 amp non contiuous

which should need 625 ampacity, but as he wrote it could possibly end up with 600 x 2.25 = 1350, continuous and non continuous load is not always the same amount.
 
Location
Ford Motor Company
Occupation
Industrial Electrician
A little late, but Thank You to all who replied to my post. One commenter stated that because of my industrial background I'm not used to sizing conductors for installation. He's right - normally the Project Engineer would do this for us to install. I was just slightly confused due to the wording of the Code and my interpretation of it.
 
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