Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
Moderator
Knifemaker / Craftsman / Service Provider
- Joined
- Feb 13, 2007
- Messages
- 19,155
I believe that sometimes an old breaker can be come weak. My old shop had a 100 amp breaker that blew sometimes with perhaps a 40 amp load on it for an hour or two. There was no way in hell I was pulling anywhere 100 amp. I replaced the breaker and the problem went away.
I'll point out there are two things that dictate wire size. The maximum amperage capacity of a wire (which can be quite high) and the run length which effects voltage drop. A high load over a long run looses power to resistance. Each foot of wire has that same resistance as the next (and the same capacity) so it doesn't get any hotter than it would otherwise. But all those feet add up, and at the end, the 110 you have at service may be 95 at the motor. Well that motor draws a certain amount of watts. So as the voltage goes down due to voltage drop, the amperage draw goes up proportionately. Thus a 15 amp motor is too much for a 20 amp circuit if it is a long run because it draws more than 15 amps as the voltage goes down. But, there is less voltage drop with larger wire.
The gauge and insulation type dictate the amperage rating of a wire, and that is what dictates the size breaker you use to protect that wire.
Just FYI.
I'll point out there are two things that dictate wire size. The maximum amperage capacity of a wire (which can be quite high) and the run length which effects voltage drop. A high load over a long run looses power to resistance. Each foot of wire has that same resistance as the next (and the same capacity) so it doesn't get any hotter than it would otherwise. But all those feet add up, and at the end, the 110 you have at service may be 95 at the motor. Well that motor draws a certain amount of watts. So as the voltage goes down due to voltage drop, the amperage draw goes up proportionately. Thus a 15 amp motor is too much for a 20 amp circuit if it is a long run because it draws more than 15 amps as the voltage goes down. But, there is less voltage drop with larger wire.
The gauge and insulation type dictate the amperage rating of a wire, and that is what dictates the size breaker you use to protect that wire.
Just FYI.