# Square D QO question

• posted on March 29, 2007, 3:36 pm
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.
Thanks, Boden

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• posted on March 29, 2007, 2:47 pm

Yes, I think they do, just for that reason.

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• posted on March 29, 2007, 7:47 pm
Meter reading will varty depending on the type meter you have.
True rms?

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• posted on March 30, 2007, 6:19 am

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.
Dave

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• posted on March 30, 2007, 9:47 pm
snipped-for-privacy@cs.ubc.ca (Dave Martindale) writes:

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.
Dave

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• posted on March 31, 2007, 2:27 am

Seems strang, have you tried swapping another 20a breaker in?
tom @ www.Consolidated-Loans.info