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I'd like to be able to power off the sub-panel in my home workshop using a simple key-based switch. I envision a junction box just before the sub-panel with a key that can be turned "on" or "off", and removed.

(The aim is to make sure children don't have access to any of the electrical equipment in my shop.)

  • Assuming the subpanel has a door, how about a padlock to block access to the breakers? – DoxyLover Aug 7 '14 at 20:40
  • You might not want to shut ALL the power off on a regular basis...workshops can be quite dangerous in the dark. – Grant Aug 8 '14 at 2:35
  • The overhead lights would be powered by the house sub-panel, and so these would always be available. The shop sub-panel would be used mainly for the receptacles that power the tools. – Michael Aug 8 '14 at 13:58
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Lockout

You could use a "lockout". A lockout is a device used by Electricians, that allows them to lock breakers in the off position. When an Electrician is working on a circuit, they will turn the breaker off, place the lockout on the breaker, place a padlock and a name tag through the lockout lock hole. This prevents others from accidentally energizing the circuit, while the Electrician is working. In most places, the Electrician is the only person with a key to the lock, and the key is kept on them at all times.

Lockout

Disconnect

An "electrical disconnect" or "safety switch" is a more permanent solution. They are available in fusible and non-fusible varieties, with a wide range of current ratings. They usually have the ability to be locked in the off position, using a common padlock.

Square D disconnect

You'll wire it up to interrupt the ungrounded conductors of the feeder to the panel.

  • Turn off the breaker in the service equipment panel that feeds the panel in the garage.
  • Disconnect the feeder wires from the panel in the garage.
  • Mount the disconnect near the panel in the garage.
  • Connect the ungrounded conductors from the feeder to the line side terminals in the disconnect.
  • Using a length of the same gauge cable as the feeder, connect the ungrounded conductors to the load side terminals of the disconnect.
  • Using appropriately sized twist-on wire connectors, other approved means, or terminals in the disconnect if they're available. Splice together the grounded and grounding conductors of the feeder and the short length of cable.
  • Terminate the other end of the short length of cable in panel.

Now when you move the disconnect into the off position, the panel in the garage should be dead. You can then lock the disconnect door closed, and the handle in the off position.

  • Or a lockout on the main breaker of the subpanel. Assuming the subpanel has a main breaker, and it has the necessary bit of metal to allow you to slap a lock there. Permanent lockout kits can also be obtained that can be retrofitted to individual breakers, I just saw one at Menards today, and they are not reputed for carrying everything a real electrical supply has. – Harper May 20 '17 at 16:26
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There are disconnects that work using an electrically-held 'contactor', however they are quite expensive for residential use.

Primarily, they're used to turn off some kind of motor or appliance, or even an entire panel in the event that someone pushes a button. They're generally configured so that while in the 'on' position, they apply the voltage needed to close the connection, allowing power to flow. Hence, if the control circuit itself loses power, it still does its job, perhaps inconveniently.

The actual buttons can operate on anything between 24V and up, depending on the configuration, and can be a key switch (though, that stops it from being considered an emergency disconnect)

You can check at your local supply house, both Square-D and Cutler Hammer make a variety of them from 30 amp / single phase ratings on up to really big stuff. Basically, your key switch is low voltage that controls a relay. The relay controls a much bigger contactor (also basically just a relay) which actually controls power to the panel.

If all you need is the ability to keep kids out, and there's no need to expand the setup to shut off your shop in the case of emergency, then go with what Tester101 suggested. And, if you're getting into control circuits (however basic) and are even a little uncomfortable, get an electrician out to help.

You can also just get a contactor rated for the amperage of your panel and a suitable listed and approved junction box, but ... don't go doing that unless you're very sure of what you're doing. Get the made to purpose one with the enclosure, ground bar, insulators for the ground bar, etc.

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