Troubleshooting/Identifying an Electrical Wiring Issue


TL;DR Our power circuit (i.e. not lights) intermittently trips the RCD usually in the middle of the night. What would an electrician do to identify the cause? Is there are device I could purchase to try and DIY diagnose (safely/legally)?

Was hoping for some advice or theories from people with experience or even perhaps a sparky if possible? I know I doubt it will be solved here given the many possible causes, but I thought I may as well give it a shot?

Since about mid December, our power circuit cuts out, usually in the middle of the night. It's never really happened before; lived here about 4 years. It happened about 5 or 6 times in December, and then only 2 or 3 times since. We haven't really bought any new electrical appliances or changed the way we do anything (especially given we are sleeping). Sometimes we have a fan and/or portable AC on, but that's about it.

I've only now started to note the dates (the two most recent ones were Jan 20th and Feb 11th). There doesn't appear to be any rhyme or reason apparent to me (except usually being in the middle of the night whilst sleeping). I think once it was during the day as we left in the morning and came back late afternoon to no power. When we notice it, all I do is go outside to the switchboard and flick the power circuit breaker back up and everything works again. No other unit has complained of anything similar.

I emailed my ex builder strata manager and he basically says I need to get an Electrician to come and fix the issue, saying it is most likely:

An overloaded circuit.
A faulty devise, switch, dimmer that triggers power shut off.
A fault in the RCD.

Any ideas how much the above would cost to fix if one or more of them was the cause?

My main concern is that because it only happens at at night intermittently (and less frequently recently), it might be difficult or impossible to diagnose, which would either waste everyone's time or result in a hefty bill by the electrician. Has anyone gone through a similar situation or know what an Electrician would do in this scenario? Would they test the circuit and/or every electronic device with a multimeter?
(or something similar, sorry I have no idea about these things, just what I've googled).

Might get roasted (pun intended) for asking, but would I be able to test electrical items if I bought some device? I don't even know what device or how much they would be?

Thanks in advance as always.

Update my wife just mentioned now (conveniently forgot to tell me at the time) the builders who were renovating our kitchen mid-late last year reported to her they experienced many instances of this happening during their couple of months renovating…so the problem existed at least since July


  • +2 votes

    I'd get a separate surge protector for the fridge. That is what I'd isolate first. It's probably the main electrical device that "kicks in".

    Do you have electric water heater? Though I doubt it would be that on it's own (the element starting to fail) .

    Could be the two of them together.

    Do you have separate meter for peak and off-peak power?


      Brand new fridge (well, August)

      No, instant gas.

      I don't think so…when I look at our electricity bill, there's only one reading and no mention of peak/off peak…


      Thanks, any specific surge protector you recommend, or would any old one do?

      • +1 vote

        I'd use any old one with a little "pop out" button thing.

        Just make sure you check the fridge once a day to make sure it is running.

        May not be the fridge.

        If your RCD trips again then flick it back on and then check fridge. if fridge is still off then check the powerboard to see if it's safety activated.

        that might give you your culprit.


          Well, we renovated our kitchen in August and moved the fridge, so a new GPO was installed…they initially installed it too low and the fridge stuck out a bit because of the power plug, so they sent two deadset kids (apprentices I suppose) back a few weeks later to move it up higher than the fridge (about a foot). They just installed a junction? Because otherwise they would have had to chase it in the brickwork again, and we said too much effort and dust.

          Unlikely, but perhaps they didn't do it well?


      I'd get a separate surge protector for the fridge.

      That (almost certainly) won't help OP diagnose or solve their problem. The trip is exceedingly unlikely to be caused by a voltage spike interacting with (or originating in) the fridge.

      Isolating the fridge is a good idea to test, but with an intermittent problem it might be a lot of nights with the fridge unplugged. Of course, as soon as the trip happens with the fridge unplugged, you can rule out the fridge, but how many nights do you run the test before giving up…

  • +1 vote

    Is it one of the circuit switches that's user replaceable ?

    If so, you could try just replacing that with the same size amperage switch from bunnings. We had one recently that decided it wanted to start tripping well below its rated current.

    As it's happening in the middle of the night it's unlikely your circuit demand would be exceeding 16a(I'm assuming that's what your breaker is rated at elec circuit )


        That RCD could be faulty?



          This guy says it is rare they are faulty, and makes a logical argument…but who knows…

          People tend to think that there RCD might need replacing or is possibly broken if it keeps on tripping, but normally it doesn’t need replacing nor is it broken in fact it’s actually doing its job. If your safety switch was broken it actually wouldn’t be tripping at all when there is a fault. If that was to happen in some cases it can then become unsafe. An example of when it needs replacing would be if it didn’t trip or if the switch gets stuck when it goes to trip and won’t release when pressing the test button on the RCD. It is recommended that every month you check to make sure that your RCD switch is working so that you and your family continue to be safe.

    • +4 votes

      please for the love of god can we not suggest to people who obviously have no electrical knowledge to replace breakers in a circuit box. Legalities aside its risk reward, reward maybe save $100 bucks - risk of electrocution.

      I am not an electrician but I do know what im doing, im happy to take the risk myself but some people just shouldnt

      • +3 votes

        hence why i said 'user replaceable'
        most people confuse plug in circuit breakers with RCD's (my post was pre picture being posted)
        plug in circuit breakers are user replaceable..

        way easier than changing fuse wire in the old days

        I'm not suggesting any non electrician deal with RCD replacement..even with elec knowledge


          I remember my dad replacing fuses in the fuse box of our house growing up. This one looks nothing like those, which is why I said I don't think it's user replaceable and I wouldn't try to.


          I agree with you mostly… but then I thought about it and maybe people who know literally nothing about electronics wouldn't be able to tell the difference between a "user replaceable circuit breaker" and a "will-electrocute-you one"…

    1. Fridge
    2. Wifi router
    3. Anything else plugged in at night?

      Router would be steady demand though.

      Fridge (or circuit for fridge) would be the main suspect.


      Lots of things (off the top of, my head…TV, set top box, microwave, alarm clock, toaster, coffee machine, dishwasher, Dyson stick vacuum and so on)…I don't turn off or unplug things every day like some might to save on standby mode.

  • +1 vote

    Check all appliances on that RCD and isolate all of them. Through the process of elimination, zoom down which appliance is the culprit.

  • +2 votes

    Might get roasted (pun intended) for asking

    Poor taste to use a pun in what is clearly a highly charged situation.

  • +1 vote

    Could be moisture in the instant hws Power outlet, I had this in heavy rain, took me a while to figure it out.

  • +1 vote

    Its the fridge. Its always the fridge.

    I don't think so…but I'm no expert.

    Picture shows you only have one power circuit, which makes it tricky to diagnose.

    But the RCD is tripping, so it is not overload. Faulty appliance, or rcd itself.


      But the RCD is tripping, so it is not overload.

      It's an RCBO which is a combined RCD and MCB, so it will trip on an overload fault.

      So it's even harder to diagnose now. ;)


        Ugh. I should have looked more closely. Also, some very faded writing above the RCBO.

        So what is the 20A MCB used for?


          It says "Main switch power"

          I'm going to guess that's for the shared laundry? We each have our own GPO's in there for our washing machines and dryers? Can't be anything else, right?

          What would the separate black/brown thing on the right be? The one that says N.L on it?

          • +1 vote

            @John Kimble: Neutral-live link. Don't worry about that.

            • +2 votes


              Neutral-live link

              Yikes, I hope not. Just "Neutral Link".

              (re. Left-most breaker) I'm going to guess that's for the shared laundry?

              Again, I hope not, there's no RCD on it. Turn it off and see what stops working :)
              If it is the laundry feed, ask the sparky to replace it with an RCD type when they come for the other problem!


    It may be a bit of a long shot but it could be ants or termites at the back of one of the power outlets causing a short. I've seen ants build a nest inside my thermostat switch on my hot water heater and also inside a mate's telephone outlet (as well as having a nest of large ants inside my computer keyboard that managed to stay undetected for some time aside from an occasional sighting on my desk (until my keyboard stopped working and I opened it up ro reveal the ugly truth).


      Probably this knowing my luck :p


        Have you had any issues with termites or ants recently? We have a lot of black ants at the moment. I would probably be getting an electrician to investigate power outlets around the kitchen first up as they will likely be nesting close to a food source. Termites wouldn't care about the food but prefer somewhere where there is moisture.

        Testing with a device in this scenario would probably not show any issues as the ants may only cause an intermittent short, however a physical inspection behind each power point with mains power switched off might show an obvious cause if ant/termite activity was high. Not advocating that you should do this yourself (dangerous power voltages can be fatal).

        Incidentally, the ants in my hot water thermostat caused it to stop working as they became squashed between the switch contacts.


          We have in the past, not recently. We had our kitchen and bathroom renovated around August, so not since then.


    Most likely the fridge. Most fridges have an auto defrost cycle, which involves a timer and heating element which melts the ice formed within the cabinet ( the random crack noise the fridge may make as the ice melts, often in the middle of the night). If you pull the fridge out and check if the evaporator bowl which is usually mounted on top of the compressor is dry, this is a fair clue something is wrong there, and the water is backing up in the cabinet and not draining out.
    Also a possible night issue, is rats moving around at night, they love to chew random cables on their rat trail, and if the its only slightly chewed, they can trip it as they run across them, happily protected by your safety switch.
    Ants in a switch or powerpoint often leave a faint brown stain around the pin openings and around the switch mechanism.
    Also worth noting, if you're going to do an isolation test of your appliances, they absoloutely MUST be unplugged, not just turned off. Any appliance with a 2 pin plug usually cant trip an rcd, but if you have a combined circuit/breaker safetyswitch combo, that may not be relevant as different faults trip each protection device but it just appears as tripped.


    Since about mid December, our power circuit cuts out, usually in the middle of the night. It's never really happened before; lived here about 4 years. It happened about 5 or 6 times in December, and then only 2 or 3 times since. We haven't really bought any new electrical appliances or changed the way we do anything (especially given we are sleeping). Sometimes we have a fan and/or portable AC on, but that's about it.

    I can't imagine you were running the portable AC in winter…

    That's a pretty likely culprit. They generate condensation… Does the trip ever happen with the AC unplugged?
    You could get a portable RCD and plug your AC into that, but it would have to be one that trips at a lower current and/or faster than your existing RCD to be of any use as a diagnostic tool (i.e. these are hard to find and expensive).

    Clean the AC unit following the manufacturer's instructions. Vacuum out whatever dust you can. See if the problem remains.


      No, not in winter. Unplugged and kept in the storeroom.

      But we've had it for years and it's not happened in previous summers. I know it's possible it could have developed a problem since.

      We've been leaving it plugged in case we want to turn on in the middle of the night.

      I actually cleaned it out recently!


        If it's not running, it won't generate condensation, so if the trip happens when you haven't been using it for a while (long enough to dry out?), that's probably not the cause. But it's worth unplugging it just to check…

        If you can't sleep, you can get out of bed and plug it back in ;)

        You mentioned above a new junction box for the fridge GPO, that is certainly a possibility. Maybe when it cools down after a humid day some condensation settles in there?

        Got any mates who are sparkies or otherwise know what they're doing around mains power?


          Unfortunately not, hence my attempt to do some basic brainstorming/troubleshooting with my trusty OZB members.

          You reckon I should just get a sparky in now, or possibly wait till it is more frequent/I have more of an idea what the cause would be? Or is that potentially dangerous?


            @John Kimble: It's not likely to be dangerous, but you may never figure it out if it only happens once a month…

            You might be able to ask around here (or airtasker) for some unqualified-but-knowledgable person to have a look (no touching!) for a 6-pack ?

            Do you have access into the wall/roof cavities where the cables go to look for vermin?

            edit: if you're looking in roofs/walls, turn off all the switches on your circuit breaker panel first.


              @abb: I can get under my unit, we are on the ground floor. No crawl space above us because there's a unit above ours, but the lights were rewired when we renovated, so unlikely to be those and they are on their own circuit anyway.

              I've been under a few times and haven't noticed anything unusual, but I wasn't specifically looking for vermin I suppose.


    Middle of the night… Any chance of a pest, such as rodent or possum making it's way past dodgy wiring?

    Of course, finding such faulty wiring may prove challenging, but if you can see the path that the pests are taking, it should reduce your search space.

  • +1 vote

    This one is very tricky to diagnose, like others said just do elimination test on each appliance to save you money first. Then call in electrician. Our house got this problem when we first moved in, happened intermittently for about 2 year(once or twice a week, sometimes a few months lapse) until it start doing this more than once a week then we called in the electrician and he went through every circuit on the board. He found that previous electrician did a dodgy job by mixing neutral and earth wire or sort of. Cost about $200+ and all good since.
    Funny enough we had one occasion while away on overseas holiday and the thing tripped, had to call friend to come in to turn it on to avoid having to sanitise the whole fridge when we got back. The annoying bit about this is you gotta have some IoT device at home to monitor outage to prevent fridge melt down.


    How old is the house?


      It's a unit. Built 1912? Power cables rewired probably 5 years ago. Light cables rewired last year.


        Ah. If it was rewired in the past decade then you probably have a different problem to mine (similar symptoms)

        Poster above me is right, its a tricky one to solve, especially if you can't replicate the fault conditions.

        Some places I would start
        -Buy an RCD tester to check RCD is working normally. Cost about $25
        -Plug a kettle and toaster into either side of the double outlet, and run together for 5 minutes straight. This should stress the cable a bit. Try it on each outlet. If your extra savvy, you can plug power board into the outlet, run the toaster off one side of the powerboard, and stick the prongs of a multimeter (set to read 240v AC) into the socket of the other side. This is verging on danger territory though. If you do it wrong you could get shocked, so its only for the experienced. It will tell you the voltage drop of the wiring under load.


          See below, but if higher chance that you have old-wiring/insulation issues, better to get that checked-out, sooner rather than later.

  • +3 votes

    The switch actually pretty unlikely to be faulty. Appears to be doing its job.
    Your updatey bit suggests everyday current leakage to earth going on, and total figure at any given point maybe only slightly below the RCD threshold. Explains builders' experience during renovations of it taking very little ruction into circuit from power tools to throw the switch.
    Read here for good summation of why may be switching in the middle of the night.

    Beyond earlier-mentioned probability of fridge contributing (not just cyclic type either - very first frost-free owned threw safety switch on a couple of occasions when playing up a bit), start by unplugging and not using any surge-protectors or powerboards with built-in, anywhere in the house.

    Irony given some other comments in thread, surge-protectors well understood to contribute some passive earth-leakage, and quite a bit if dodgy in design or when some components degraded by actually having shunted a few spikes. A real phenomenon, sometimes, preceding any failure of components further along.
    If you have only a few in the house, removing them to see if no recurrence of your problem, very likely cheaper than calling out an electrician. Removed gear can be tested at later date.

    Partly contrary to that link, consider buying UPS for computer and other sensitive equipment, if don't have one. All UPS units have spike-protection circuitry onboard, can't avoid. Just don't be fussed into buying surge-protected other stuff, as more than anything each new powerboard or plug-in just increases likelihood that you'll end-up with a crappy one.
    Bonus of UPS is that nagging alarm will likely wake you up in middle of the night, if power does goes off again!

    If above doesn't improve situation, and certainly prior to getting in an electician, you can become methodical about leaving other stuff unplugged for a period of time, however tedious that may be for you.

    Best of luck with the issue.

  • Top