Strange Circuit Breaker, Power Trips Every Night at Midnight

Hi all,

Just bought a new property and have a room that has some odd wiring. Have already asked the electrician and he’s narrowed it down to what he says is this breaker on a sub panel. It trips every night at exactly midnight. Apparently it is a special type of circuit breaker.

Can anyone explain why you would wire this way?

Here’s a photo:


  • You have a Shunt Trip, question is, why is it there?

    It is basically a manual emergency circuit breaker, and obviously something is triggering it at midnight. Either follow the wiring and find out what is, or just disconnect the damn thing.

    Did the sparky not explain it to you, or find out what it is connected to?

    • They wanted to bill me for 4 hours so I said I’ll just have them come back when I have a plan.

      • 4 Hours to trace the wiring? 4 hours seems excessive unless it is a prick of a property to do that in.

    • It's a manual shut off not a solenoid driven so there is no return.
      Think of a mobile phone just on a larger scale it all works then hook a shunt to the speaker. It all works fine then someone calls the phone it sends power to the speaker and to the shunt hooked into the speaker wire causing it to shut off. Manually restart phone all works then someone calls bang it's off again.
      This is if it's working correctly.

      Cut the circuit and terminate as you say job done it's been setup as a signal wire not a safety switch. I think it's faulty but read my other comment bellow on that

  • If it is tripping at the same time every day, it probably has a timer attached to it.

    • Correct !
      Something that goes off the same time every day.
      Possibly Off-peak hot water.
      Or if you have a smart meter - something you have timed to start at midnight

  • I think it's faulty they're meant to trip and it will become more frequent if it is. He probably put it in as he has ran out DIN rails to comply with the law having safety switches installed.
    Call a sparky in change to a larger board and replace with safety switches shouldn't take more than 2 hrs and it will be done properly.
    Never seen this in residential either the previous owner must of been in commercial construction stolen it from work and thrown it in.

  • is it when the fridge cycle kicks in?

  • Hot water heater starting up with off-peak power?

  • turn your fridge off at 11pm for couple of hours, i bet all the frozen food in your fridge it is the defrost cycle.

  • +5 votes

    Does the time it trips change with daylight savings?

  • Your neighbour steals your power for their ganja garden.

  • get the sparky to update the circuit board so each circuit is an RCBO combo (rcd and breaker). bring it in line with the current standard.

    If it's tripping at the same time, either on a timer, or something releated to heating/cooling.

    not an electrician, my 2c

  • If it's tripping at the same time, then it's something on a timer. Is there a pool? Is there under floor heating? Are there outside lights? I'd hunt for anything that might be a timer.

  • We use these in server rooms with sprinkler systems. 24 volts will trip the circuit breaker allowing ups to take control and shutdown servers in case they get wet.( if there is a real fire that pops the sprinkler heads.

  • It's tripping because it's was used to power something Off Peak, maybe Spa/Hot Tub circuit.

  • How accurate is the timing? Merely "near" midnight each night, or on the dot? Did it change with daylight savings recently?

    Any nearby heavy machinery / industrial sites? Do your lights flicker (if you still have any incandescents)? My first guess is that something big is turning on each night affecting your supply enough to trigger the shunt.

    Second guess is that power companies using signalling in the power feed to make changes for smart meters etc. (e.g. start of off-peak period). Older equipment ignores it, but something slightly faulty may be tripping over it.