Handbook example

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OrlandoCB

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Good morning,
Trying to figure out this example from the handbook but got no idea why they worked it liked that
Capture.JPG
Why would you go to 2 AWG cable when the 3 AWG cable is suitable for the job? We could just go to 85 amps on cable and thanks to the next size up rule on CB i could use the standard 90 size.
Am i missing something here ( Bet i am )
 
I can't answer as to why they show using #2 AWG for the panels. But the whole example is for sizing the service entrance/feeder conductors. It wasn't meant to focus on the feeder tap conductors. Although I think they should show everything in the example correctly, the focus is on the main feeder sizing.
 
I believe they are applying 110.14(c) and using the 60° rating of the #2 (95 amps) and "next size up".
There was no indication that the meter or panel are both 75° rating so they used the 60°.
 
augie47 said:
I believe they are applying 110.14(c) and using the 60° rating of the #2 (95 amps) and "next size up".
There was no indication that the meter or panel are both 75° rating so they used the 60°.
Click to expand...

Morning Augie47,
Buy why would they go to #2 if #3 is already enough for the load (85 amps at #3 to 80 of the load)
 
infinity said:
Because #3 at 60° C is 85 amps and the next size up rule would be 90 amps not 100.
Click to expand...

Good evening infinity,

Think I'm missing something here, not sure if its like this:

if you go to #3 AWG at 60 C that gives you 85 amps, and the load is only 80 amps so you can use a 90 breaker for the next size up rule (230.90)

from your post , and according to the example isn't 80 what we need and we can get it on #3 ?

Thanks for you help infinity!
 
OrlandoCB said:
Good evening infinity,

Think I'm missing something here, not sure if its like this:

if you go to #3 AWG at 60 C that gives you 85 amps, and the load is only 80 amps so you can use a 90 breaker for the next size up rule (230.90)

from your post , and according to the example isn't 80 what we need and we can get it on #3 ?

Thanks for you help infinity!
Click to expand...

The OCPD in the graphic for each panel is 100 amps so you need a 100 amp conductor or a 91-99 amp conductor that you would use with the next size up rule.

When you apply the next size up rule to your 85 amp #3 conductor you end up with a 90 amp conductor. Since your OCPD is 100 amps the #3 at 90 amps is too small.
 
OrlandoCB said:
Good evening infinity,

Think I'm missing something here, not sure if its like this:

if you go to #3 AWG at 60 C that gives you 85 amps, and the load is only 80 amps so you can use a 90 breaker for the next size up rule (230.90)

from your post , and according to the example isn't 80 what we need and we can get it on #3 ?

Thanks for you help infinity!
Click to expand...


Yes but we have to assume there are 100 amp breakers in those panels. In that case the wire must match the overcurrent protective device.
 
infinity said:
The OCPD in the graphic for each panel is 100 amps so you need a 100 amp conductor or a 91-99 amp conductor that you would use with the next size up rule.

When you apply the next size up rule to your 85 amp #3 conductor you end up with a 90 amp conductor. Since your OCPD is 100 amps the #3 at 90 amps is too small.
Click to expand...

Crystal clear now!!!,
thanks Infinity
 
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