Can I ignore 310.15(B)(7)(c)?

[de2]

I am sure all of you have one or more objections to NEC. And I do definitely have one; 310.15(B)(7)(c).

Single family residential, calculated load is 135A.

Here is what I want; 150A OCPD with 1/0 cable (75C).

I don't feel comfortable using 310.15(B)(7)(c), 135*0.83=112A, selection #1 awg with 150A OCPD. Why would you choose OCPD based on calculated load but feeder with 0.83?

Why not chose OCPD and feeder together 0.83? Or just erase 0.83?

I see a benefit 0.83 gives, smaller cable, economical, but why keep OCPD still at %100?

I just dont get it.

 

[ActionDave]

NEC load calcs a ultra conservative. Take a look at the wire the power company uses compared to what the NEC requires.

 

[infinity]

I am sure all of you have one or more objections to NEC. And I do definitely have one; 310.15(B)(7)(c).

Single family residential, calculated load is 135A.

Here is what I want; 150A OCPD with 1/0 cable (75C).

I don't feel comfortable using 310.15(B)(7)(c), 135*0.83=112A, selection #1 awg with 150A OCPD. Why would you choose OCPD based on calculated load but feeder with 0.83?

Why not chose OCPD and feeder together 0.83? Or just erase 0.83?

I see a benefit 0.83 gives, smaller cable, economical, but why keep OCPD still at %100?

I just dont get it.

Your calculation is incorrect. It's 83% of the service rating not the calculated load.

 

[augie47]

Your calculation is incorrect. It's 83% of the service rating not the calculated load.

In this case I think you still end up with a #1. 135 amp calculated load =150 amp service 150 X .83 = 124.5 = #1 but that is the same case as it was u8nder the "old" rule.

Remember the NEC is the MINIMUM.

 

[de2]

Your calculation is incorrect. It's 83% of the service rating not the calculated load.

what is service here? which piece of equipment is service and what is the rating of it?

 

[hbiss]

what is service here? which piece of equipment is service and what is the rating of it?

Didn't you tell us 150A??

-Hal

 

[de2]

Didn't you tell us 150A??

-Hal

SO "service" here indicates the 150A OCPD after the meter? Is that what you mean by service?

 

[Dennis Alwon]

Yes the service overcurrent protective device in your case would be the service size.

For instance a 200 amp service would need a conductor capable of handling 166 amps-- 2/0 copper would work

 

[de2]

Yes the service overcurrent protective device in your case would be the service size.

For instance a 200 amp service would need a conductor capable of handling 166 amps-- 2/0 copper would work

is there any logical explanation that you put a smaller cable than ocpd? I just dont get it.