And in comes the ELECTRICIAN to answer the question for once and for all...
First, some people brought up the "boxes with levers that can be locked up or down". THESE ARE NOT BREAKERS! These are knife switches with FUSES inside, one for each
phase. If the handle is still up, (thus the
knife switch closed) the
circuit can still open (in part or in whole). When the fuses go, the handle DOES NOT MOVE. Hopefully there is an interlock in place in many of these situations to "open" the other phases, to prevent things from still operating and causing damage. Not always the case.
SECOND, there are many types of breakers. SOME are designed to still trip with the handle "locked" on. This is a common practise for things like fire-alarm systems where you don't want them turned off accidentally. This is completely legal, IF the breakers are designed in this way.
You can buy locks for these panelboards (
breaker boxes,
etc) that are designed for this purpose. Note that some of these are designed so that the
breaker handle can still reach the "tripped" position, and others are not.
SOME breakers are designed so they STAY ON when the handle is "locked on", it is illegal to lock these on.
THIRD, in general most tape will still give way to the
breaker to move to the "tripped" position.
It should be re-iterated that these breakers, may or may-not be designed to be "switched" on a regular basis. Many breakers actually degrade over time when you keep switching them off regularly. These breakers are meant for OVERCURRENT PROTECTION and as a DISCONNECTING MEANS, not as a regular
switch. If you are using them often to turn something on-and-off every day you should think about hiring an electrician to come in and install an appropriate
switch(es), in a more convenient place even to use most of the time.
And yes the
breaker locks can also be installed to lock a
circuit breaker "off" as a
safety precaution (In Canada at least you MUST use a "lockout tag" that clearly says that it should not be turned on,
etc). This is also not for a
circuit that is no-longer "installed". The
breaker should be REMOVED. I've seen people do that before.
Anyways, so as long as these breakers are designed to still trip when mechanically interfered with, it's all good. However It's probably just as good idea to install another method for power-down or just to clearly label the ones to stay on.