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The National Electric Code (NEC) Section 422.30 requires "permanently connected appliances" to have "lockable" disconnects, so that power can be reliably cut to the appliance when it is serviced. Here is an example of a lockable circuit breaker for a built-in oven: Lockable circuit breaker

This seems like a great fail-safe to prevent someone from flipping a circuit breaker on while someone else is in contact with a conductor on the circuit. My question is: Why are lockable disconnects only required for hard-wired appliances?

The picture here shows a 240V 40A circuit, but the NEC rule applies to any appliance rated over 300VA, so such locks also appear on 120V 15A breakers for hard-wired appliances. But anyone working on a simple wall outlet or light switch could be exposed to at least 1800VA if the circuit breaker were unexpectedly turned on. So why does the NEC only mandate locks on some appliance circuits, and not all circuit breakers? Do appliances pose a different and greater hazard than other hot conductors?

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Yes, they do pose a different hazard.

When someone is working on building wiring, receptacle, switch, etc., it is very easy to wrap up any problem areas if the work can't be completed in a single work session. (Yes, lockouts can be useful any time, but in a typical situation you can let everyone know "the electrician is on site, don't touch the main panel, and that is quite effective for a short period of time.) If work can't be completed in a single session, you can cap wires with wire nuts and generally make things "safe" - the one exception might be known damage to wires in a wall, in which case the wires will likely need to be replaced and the first step would be to disconnect at a junction box or at the breaker, depending on the situation.

Not so with appliance repairs. If you have a major appliance repair, it is quite possible that you will have the appliance opened up with parts all over the kitchen or HVAC closet. It is also quite possible that the design is such that disconnecting and capping the wires coming into the appliance will actually complicate testing of repairs, depending on where the wires enter the appliance. And then you find that the widget is the 2002 model instead of the 2001 model and it won't work and you have to go back to the parts store to get a replacement. And they're closed for the day so you have to come back tomorrow. And you really don't want to put everything back together and the homeowner doesn't want to pay for yet another extra hour of labor for you to put it together still not working and take it apart again. So the lockout now becomes key to make sure that somebody else, who wasn't around when the repairs were being done doesn't:

  • Come home and find the house is cold
  • Mess with the thermostat and find heat is not coming on
  • Go to the main panel and see the breaker OFF and flip it ON (having no idea why it was turned OFF)
  • Hear a very loud noise from the HVAC closet because tools, screws, etc. shorted out something or
  • Go to the HVAC closet because the heat still isn't coming on and touch something exposed that turns out to be energized
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  • Interesting: So this is code was developed because there are more ways and it is more likely for an appliance to be left in an unsafe condition for an extended period? Perhaps this warrants another question: But wouldn't it be as effective and easy (and code-compliant) to remove the panel cover and hard disconnect it there (by either putting insulating tabs over the mains where the breaker connects, or by unscrewing and capping the hot line out(s) from the breaker)? – feetwet Dec 15 '19 at 6:02
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    So this is code was developed because there are more ways and it is more likely for an appliance to be left in an unsafe condition for an extended period? I think so. But I don't know the history, so I can't say 100% for sure. As far as removing the hot from the breaker - remember that the appliance repair person may not be an electrician - putting a lockout is trivial (anyone can do that), but messing with the wires going into breakers is not (relatively speaking). Plus those wires are not normally moved around much, especially the bigger wires. The code wants "easy" - if it ain't – manassehkatz-Moving 2 Codidact Dec 15 '19 at 6:14
  • easy then people won't bother and won't be safe. – manassehkatz-Moving 2 Codidact Dec 15 '19 at 6:14
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Why are lockable disconnects only required for hard-wired appliances?

Because if they plug in, you can just unplug them :)

The purpose of disconnects, whether this type or those in fluorescent lights, is to allow you to unhook it when hardwiring.

The purpose is for lockout/tagout

This is why Code requires a disconnect switch within line-of-sight of the equipment in question. That is true in all instances; mainly this is applicable to industrial.

If a line-of-sight disconnect is not practicable, then Code is allowing a lockout/tagout device in its stead.

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