I have a Nutone central vacuum on a dedicated 20 amp, 120v circuit. The
vacuum is spec'd to draw 12.6 amps (I measure it at closer to 13.5 amps)
but the starting current is close to twice that. Consequently the
breaker opens at least half the time at start-up.
Does Square D make a QO 20 amp breaker with a delay characteristic?
Perhaps a thermal breaker?
Although the circuit is dedicated, running 10AWG in order to put in a 30
amp breaker will not be fun.
Sounds like you have a weak breaker. A 20 amp breaker should take at
least 20 seconds or so to trip when the load is 40 amps. Your load is
apparently around 25 amps, and at that current it should take many
minutes to trip. Meanwhile, the central vac should be up to speed, and
the current down at 13.5 A, in less than 20 seconds.
Here's an example trip curve for one model of QO breaker. The same site
has many others if you know exactly which model of breaker you have.
Another example: our central vac is a two-stage (two fans in series, two
motors) rated somewhere around 13 A. It's plugged into a circuit with a
15 A breaker. It *never* trips the breaker when started.
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