Sizing Conductor For Breaker

[mstrlucky74]

In picture attached the 225AF is frame size but you would size wire to the trip which is 80A, correct? Thanks.

 

[charlie b]

More precisely, you choose the trip setting based on the ampacity of the conductors, after you have chosen the ampacity value based on the calculated load. But yes, you are right.

 

[jumper]

To add to what Mr B said. The AF is not only the frame size, but maximum allowed ampacity of the breaker.

http://www.eng-tips.com/faqs.cfm?fid=1801

 

[mstrlucky74]

Thanks.

 

[mstrlucky74]

Btw...they are running 3/0 Al wire. Seems way oversized although the run is 300'.

 

[Ingenieur]

Btw...they are running 3/0 Al wire. Seems way oversized although the run is 300'.

likely v drop
what voltage?

 

[infinity]

Btw...they are running 3/0 Al wire. Seems way oversized although the run is 300'.

Way oversized. According to my VD calculator using maximum values (300', 80 amps) for 208 volts the minimum conductor size for less than 3% VD is #1 AWG, for 480 volts it's #3 AWG.

 

[Ingenieur]

using southwire calc
3 ph 208
al
conduit
3% drop
300'
80 a

3/0 2.7%

~ the same by hand

 

[infinity]

using southwire calc
3 ph 208
al
conduit
3% drop
300'
80 a

3/0 2.7%

~ the same by hand

For some reason I decided to use copper in my calc's. :slaphead:

 

[Ingenieur]

For some reason I decided to use copper in my calc's. :slaphead:

I did too, first time
I hardly ever see al other than oh service or when the util pulls ug

 

[mstrlucky74]

More precisely, you choose the trip setting based on the ampacity of the conductors, after you have chosen the ampacity value based on the calculated load. But yes, you are right.

Ty