200A Residential Service Entrance & 230.42

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tryinghard

tryinghard

Senior Member
Location
California
I?m installing a 200A meter main and want to double check the service entrance size, an Article 220 load calc equals 144A. Is 1/0 cu THHN compliant for the service entrance?
 
ron said:
Table 310.15(B)(7) seems to be based on service size. Service size is based on calculated load.

Table says 2/0AWG CU is the minimum
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You beat me to it.
Is table 310.15 (B) (7) in to 2011? I don't see it in 2008. It's 310.15 (B) (6)
 
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Also watch 230.90. If you have a 200A single disconnect, then you need to size the conductors for that 200A breaker, not the calculated load (although the calculated load must also be less than the disconnect rating too).

In a residential install, you can use 310.15(B)(7) to determine what is legal for a 200A disconnect. If you had a 150A main installed in that meter main, you could use #1 copper for a dwelling service, or 1/0 copper for a commercial service.

If the Service disconnect had multiple devices (e.g. up to the 6 "mains" allowed), then you'd be allowed to size the wires for the 144A calculated load and the sum of the disconnects could be well over 150A. Not that I'd recommend it though...
 
tryinghard said:
The first two sentances of 230.42 seem to say ampacity per Art 220, but then 310.15 must trump?
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Art 220 doesn't say anything about ampacity, Art. 220 is about the "load."

230.42 says loads shall be determined by Art 220 and Ampacity shall be determined by 310.15.
 
david luchini said:
Art 220 doesn't say anything about ampacity, Art. 220 is about the "load."

230.42 says loads shall be determined by Art 220 and Ampacity shall be determined by 310.15.
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What I mean is how 230.42 starts "The ampacity of the service-entrance conductors...shall not be less then either 230.42.A.1 or A.2"
 
tryinghard said:
What I mean is how 230.42 starts "The ampacity of the service-entrance conductors...shall not be less then either 230.42.A.1 or A.2"
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I'm still not sure I understand what you mean. It says the ampacity of the service-entrance conductors shall not be less than 100% of the non-continuous load plus 125% of the continuous load, OR not less than 100% of the non-continuous plus continuous load when you have a 100% rated OCPD assembly.

The load shall be determined from Article 220, and the ampacity shall be determined from 310.15.
 
david luchini said:
I'm still not sure I understand what you mean. It says the ampacity of the service-entrance conductors shall not be less than 100% of the non-continuous load plus 125% of the continuous load, OR not less than 100% of the non-continuous plus continuous load when you have a 100% rated OCPD assembly.

The load shall be determined from Article 220, and the ampacity shall be determined from 310.15.
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appears to state ampacity of SE conductors two different ways (but I think I'm over-reading it):
1 - "The ampacity of the service-entrance conductors...shall not be less then either 230.42.A.1 - the sum of the noncontinuous loads plus 125% of continuous loads..."
and
2 - "Ampacity shall be determined from 310.15"
 
tryinghard said:
appears to state ampacity of SE conductors two different ways (but I think I'm over-reading it):
1 - "The ampacity of the service-entrance conductors...shall not be less then either 230.42.A.1 - the sum of the noncontinuous loads plus 125% of continuous loads..."
and
2 - "Ampacity shall be determined from 310.15"
Click to expand...

Yes, I think you are over-reading it...

1. The ampacity of the service entrance conductors shall not be less than the sum of the non-continuous loads plus 125% of the continuous loads. Imagine if you had a 200A load that was 100A continuous and 100A non-continuous. 230.42 tells you that you need a conductor that has an ampacity that is not less than 100A + 1.25*100A = 225A. Now that you know that you need a conductor with an ampacity of at least 225A, how do you determine what size that conductor will be?

2. Conductor ampacity is determined by 310.15. You would go to section 310.15 to find a conductor size that would have an ampacity of at least 225A.
 
200A Residential Service Entrance & 230.42

Got it, you explain it good. My case conductor rated not less than 144A but requires at least 2/0 cu


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