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My newly installed Insinkerator Evol Plus garbage disposal runs when switch is turned to off, trips breaker when switched to on. I tried it on a shared circuit. Now it's hardwired to it's own dedicated 15 amp circuit. Replacing the switch didn't help. Is this brand new disposal defective?

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Sounds like your wiring job is defective, how did you connect the switch? – BMitch Aug 31 '13 at 17:23
That sounds like a switch wired in parallel instead of series. – Kevin Reid Aug 31 '13 at 21:06
Wires from circuit breaker and disposal both meet at switchbox, pigtailed into switch. Black to black, white to white, ground to ground. – Dan Aug 31 '13 at 23:09

You incorrectly wired the switch into this device. What you've created is an always on device and a short in the middle of the circuit:

      Black --------+-----------+
                    |           |
line              switch      disposal
                    |           |
      White --------+-----------+

In this scenario, when the switch is flipped, you create a short circuit that trips the breaker, and there's nothing preventing power from always going to the disposal.

Instead, what you need is to switch the hot, so that power is turned off to the appliance when the switch is opened. Note, you don't switch the neutral since that would result in power going to the appliance and becoming a shock hazard should anything make a path available to ground.

      Black =---+-switch-+------+
line                         disposal
      White --------+-----------+
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Got it. Works now. Thanks. – Dan Aug 31 '13 at 23:59
@Dan - If you re-used the switch that you had repeatedly tripped the breaker with, when it was wired incorrectly, it would be advisable to replace it with a new one. The contacts inside the switch were likely severely pitted and damaged due to the short circuit operation. – Michael Karas Sep 1 '13 at 16:21

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