jim k
Member
- Location
- Northwestern Oregon
I?m a home inspector seeking understanding . . .
The AC nameplate tells us the minimum circuit ampacity and the maximum fuse or breaker size. Usually, the breaker or fuse is rather larger than what we would expect given the ampacity of the circuit conductors.
As I understand it, the reason for this is that the compressor motor?s built-in thermal protection is providing overload protection to the entire circuit, so the breaker or fuse need only protect against ground faults and line-to-line shorts. Also, if we were to use a conventionally sized breaker or fuse, we?d get lots of nuisance trips because of the compressor?s high draw at start-up.
Am I doing ok so far?
So my question is, if the breaker or fuse is only there to protect against shorts and ground faults, why is its size critical? Oftentimes the nameplate will specify an odd size breaker such as 45 amps. If one were to use a 50 amp breaker or, for that matter, a 60 amp breaker, why would that be a bad thing? (Other than, of course, 110-3(b) or ?because we say so.?)
Wouldn?t a larger breaker protect against faults & shorts at something very close to the same level as a smaller breaker?
- Jim Katen, Oregon
[ May 31, 2005, 06:12 PM: Message edited by: jim k ]
The AC nameplate tells us the minimum circuit ampacity and the maximum fuse or breaker size. Usually, the breaker or fuse is rather larger than what we would expect given the ampacity of the circuit conductors.
As I understand it, the reason for this is that the compressor motor?s built-in thermal protection is providing overload protection to the entire circuit, so the breaker or fuse need only protect against ground faults and line-to-line shorts. Also, if we were to use a conventionally sized breaker or fuse, we?d get lots of nuisance trips because of the compressor?s high draw at start-up.
Am I doing ok so far?
So my question is, if the breaker or fuse is only there to protect against shorts and ground faults, why is its size critical? Oftentimes the nameplate will specify an odd size breaker such as 45 amps. If one were to use a 50 amp breaker or, for that matter, a 60 amp breaker, why would that be a bad thing? (Other than, of course, 110-3(b) or ?because we say so.?)
Wouldn?t a larger breaker protect against faults & shorts at something very close to the same level as a smaller breaker?
- Jim Katen, Oregon
[ May 31, 2005, 06:12 PM: Message edited by: jim k ]
