I just bought a dust collector. The vendor says it draws 20a and requires a 40a circuit. I asked around and most users put in a 30a circuit and never have a problem.
I wired it up temporarily and found it draws 140a for less than a second and then quickly drops to 20a.
I looked up Square D's trip curve. They say that 5x the rated load will trip a breaker between 4 and 12 seconds. So my 140a is less than 5x the 30a rating, and only occurs for a split second. So, a 30a breaker ought to be okay, right? Even if my meter is reading low, it will take 210a for 2 seconds; and it couldn't possibly draw 210a.
140a seems like a lot of current and I am a little surprise they design breakers to stay open that long. Since it sounds odd to me, I just want to check to see that I am understanding it right.
For bonus points, if someone wants to explain how a 3hp motor can draw 20a, I would like to know. I thought maybe that was with no load, but it is 20a while working the machine. Seems really really high.
I wired it up temporarily and found it draws 140a for less than a second and then quickly drops to 20a.
I looked up Square D's trip curve. They say that 5x the rated load will trip a breaker between 4 and 12 seconds. So my 140a is less than 5x the 30a rating, and only occurs for a split second. So, a 30a breaker ought to be okay, right? Even if my meter is reading low, it will take 210a for 2 seconds; and it couldn't possibly draw 210a.
140a seems like a lot of current and I am a little surprise they design breakers to stay open that long. Since it sounds odd to me, I just want to check to see that I am understanding it right.
For bonus points, if someone wants to explain how a 3hp motor can draw 20a, I would like to know. I thought maybe that was with no load, but it is 20a while working the machine. Seems really really high.