4 ms·

Feed power in through one circuit back to the main board, on a different circuit cause a short, main breaker trips, main board is now isolated from the grid. T

Feed power in through one circuit back to the main board, on a different circuit cause a short, main breaker trips, main board is now isolated from the grid. Technically possible, irresponsible, bad advice, and probably won’t work in most scenarios.

mulmen 2y ago
This is why we have regulations.
rtkwe 2y ago
Doesn't work and would likely cause fires. First the smaller circuits will trip first, that's where the current is actually flowing, there wouldn't be any actually flowing through the whole house breaker in your idea. The main circuit to your house is 100+ Amps (this would be a tiny old circuit most houses have larger main feeds these days) at least. You'd have to feed at that much through the main disconnect for it to trip. Second even if you could push that many amps through the main breaker somehow to trip it you'd be feeding it through wires designed for 15-20 amp nominal loads which would cook them.
- TheSpiceIsLife 2y ago
  You’re right, my mistake.
- cwillu 2y ago
  > Second even if you could push that many amps through the main breaker somehow to trip it you'd be feeding it through wires designed for 15-20 amp nominal loads which would cook them. Well, you'd end up tripping the 15-20 amp breaker protecting those wires first.
  - rtkwe 2y ago
    Probably but I'd rather never send that big of a pulse down a 15/20 amp line at all.
    - cwillu 2y ago
      It's no more of a pulse than any other dead short that would trip the breaker instantly rather than on a delay. The fault current that a breaker is required to be able to interrupt is two orders of magnitude larger than we're talking about feeding into the wire, and a 15 amp breaker is designed to _not_ interrupt a 150 amp load until a second has passed (there's a rating curve for this): some loads might require that much current briefly, and the wire in the wall is not going to overheat in that time (that's why the breaker has the curve that it does: to model and therefore protect the allowable heating of the wiring).
      - rtkwe 2y ago
        Yeah should be fine but I'd still rather not intentionally try it and count on it. Breakers can fail closed. Doubly so because it doesn't even do what we want it to which would be to switch the main breaker off.
        cwillu 2y ago
        Don't get me wrong, it's still a stupid thing to do, but not because there's any danger to the wiring.

mulmen 2y ago

This is why we have regulations.

rtkwe 2y ago

Doesn't work and would likely cause fires. First the smaller circuits will trip first, that's where the current is actually flowing, there wouldn't be any actually flowing through the whole house breaker in your idea. The main circuit to your house is 100+ Amps (this would be a tiny old circuit most houses have larger main feeds these days) at least. You'd have to feed at that much through the main disconnect for it to trip. Second even if you could push that many amps through the main breaker somehow to trip it you'd be feeding it through wires designed for 15-20 amp nominal loads which would cook them.

TheSpiceIsLife 2y ago
You’re right, my mistake.
cwillu 2y ago
> Second even if you could push that many amps through the main breaker somehow to trip it you'd be feeding it through wires designed for 15-20 amp nominal loads which would cook them. Well, you'd end up tripping the 15-20 amp breaker protecting those wires first.
- rtkwe 2y ago
  Probably but I'd rather never send that big of a pulse down a 15/20 amp line at all.
  - cwillu 2y ago
    It's no more of a pulse than any other dead short that would trip the breaker instantly rather than on a delay. The fault current that a breaker is required to be able to interrupt is two orders of magnitude larger than we're talking about feeding into the wire, and a 15 amp breaker is designed to _not_ interrupt a 150 amp load until a second has passed (there's a rating curve for this): some loads might require that much current briefly, and the wire in the wall is not going to overheat in that time (that's why the breaker has the curve that it does: to model and therefore protect the allowable heating of the wiring).
    - rtkwe 2y ago
      Yeah should be fine but I'd still rather not intentionally try it and count on it. Breakers can fail closed. Doubly so because it doesn't even do what we want it to which would be to switch the main breaker off.
      - cwillu 2y ago
        Don't get me wrong, it's still a stupid thing to do, but not because there's any danger to the wiring.