Ampacity different ???

Hi
why ampacity is different here?

thru #12 copper, protected by a 30 fuse I can supply a motor

but for ltg load I need #12 copper thru 20 fuse max

Tanx

Toros said:

Hi
why ampacity is different here?

thru #12 copper, protected by a 30 fuse I can supply a motor

but for ltg load I need #12 copper thru 20 fuse max

Tanx

Click to expand...

For the motor, the starting current will be higher than the ampacity of #12, but will not damage the wires.
A short circuit will be protected just as well by a 30A as by a 20A.
And long term overload of the wires will be protected by the motor overload device.
In a lighting circuit there is no such separate overload, so the breaker must serve that function too.

The ampacity of the conductor has not changed, just the overcurrent protection rules are different.