Circuit breaker popping when power restored.

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Beavis

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#273116 5-Aug-2020 10:37

Hi. My house has the older style plug in wire fuses on the fuse box. A few have 16 amp circuit breakers. My problem is if the power goes off, when the power comes on again, occasionally the circuit breaker that the 2 fridges is on trips. It must be the initial power on surge.
Reading on the internet, seems there are different surge ratings on circuit breakers. Mine are B, but looks like C might be the answer. A friend suggested I just fit a 16 amp wire fuse... what do you guys think?

Thanks

Peter.

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#2534989 5-Aug-2020 10:39

I have circuit breakers in an old house, they never trip when power comes back on. I wouldn't go back to fuse wire, I'd ask an electrician or get one in to have a look.

Jaxson

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#2535010 5-Aug-2020 11:17

Personally I'd get that one troublesome unit replaced with a modern device.

After that you'd need to look at why there is such a start up rush, and check if you have heaters/electric blankets etc on that same circuit that could be separated.

At the end of the day, these are protection devices, so they may be telling you something quite valid that you're looking at ways to ignore.

andrewNZ

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#2535046 5-Aug-2020 12:28

Those plug in circuit breakers get temperamental with age particularly the older round button ones.

Combine that with the initial demand of two compressor motors trying to start at once and whatever else is on the circuit...

It'd definitely be worth trying replacing it for a start.

Edit: DON'T replace it with a bigger one! Only an electrician can do that once they have checked that the circut can carry both the rated current of the breaker & the current required to trip the breaker.

Worst case, a larger breaker doesn't trip for a fault and burns your house down.

JeremyNzl

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#2535101 5-Aug-2020 12:57

When all devices are off and all turned off at once you are getting a maximum demand that could be exceeding you fused limit.

Normally this would be brief and most breakers will handle a % of over current for a period,

The different curve breakers are for motor starting in industrial or specialized applications where this inrush is expected and very brief.

For insurance purposes, get a sparky to have a look and test the circuit and identify the sizing of the circuit wire and the load you are running on it.

Sometimes there can be something developing and you may be thankful the situation you describe and brought it to your attention.

Bung

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#2535103 5-Aug-2020 13:00

Do you have to have both fridges on the same cicuit or is it actually a fridge / freezer pair?

timmmay

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#2535119 5-Aug-2020 13:21

It is sometimes worth getting a sparky in when odd things happen. For example, we found sometimes if we touched the metal dishwasher and metal kettle at the same time we sometimes felt a tingling. Electrician found the circuit was faulty, possibly chewed through by rats last year when they were everywhere, and we had to put a new circuit in.

neb

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#2535132 5-Aug-2020 13:33

JeremyNzl:
The different curve breakers are for motor starting in industrial or specialized applications where this inrush is expected and very brief.

In terms of fixing this at the other end, you can also get inrush current limiters/motor soft starters that will help deal with this. Alternatively, delay-start devices that ensure all the high-power loads don't start at the same time. So it's quite fixable without having to play Russian roulette with your wiring.

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tripper1000

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#2535241 5-Aug-2020 15:23

As others have mentioned the CB's don't last for ever. Replace it and if symptom persist see a professional.

Generally they're designed to remain on for a brief and passing overload and this aspect of the design may have failed. I have also seen them pop at lower and lower currents as they age. Someone may have even dropped it, damaging the internals.

frankv

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#2535266 5-Aug-2020 15:53

Plug one of your fridges into another circuit?

neb

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#2535400 5-Aug-2020 17:41

Speaking of soft starters, there's a bunch of these available from the usual suspects for a lot less than the eyewatering prices local sources charge, but they're handcrafted from the finest Chinesium so who knows how safe/reliable they actually are. Does anyone have any experience with them?

Tracer

343 posts

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#2535474 5-Aug-2020 20:32

A B curve breaker is not appropriate for inductive loads like motors. C curve is general purpose and basically all you should find in houses. B and D are for more specialised scenarios.

richms

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#2535488 5-Aug-2020 21:13

I have the same thing if I turn the main switch off, things will trip when I turn it back on, often the 63A on the meter board will. However if its coming back from a powercut its fine, I guess because everyone elses inrush currents are limiting the voltage rise to a degree so its not enough to trigger the magnetic part of the breaker.

Richard rich.ms

gregmcc

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#2535489 5-Aug-2020 21:17

Tracer:

A B curve breaker is not appropriate for inductive loads like motors. C curve is general purpose and basically all you should find in houses. B and D are for more specialised scenarios.

B curve circuit breakers are quite common in the UK in the domestic area, in NZ C curve are the more common circuit breakers, with D curve usually used for motor related circuits.

Unless you have some more specialized knowledge in the electrical area don't go buying a D curve to replace your existing circuit breaker as there are a bunch of other things like loop impedance of the whole circuit to take in to account otherwise the circuit breaker will not trip under fault conditions in the required time - This means fire and/or electric shock.

Beavis

159 posts

Master Geek

#2535509 6-Aug-2020 00:04

Thanks everyone. I decided just to buy a replacement CB, but this time got a C not a B. Seems to have fixed the problem so far. So faulty CB or one with higher surge capacity. Has fixed problem and don’t see it as a burning down the house issue. Still a 16 amp CB, just may take another second or so...

Thanks.

neb

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#2536514 8-Aug-2020 00:56

Another option is to fit an inrush current limiter, e.g. this Meanwell one, which is fixing the problem rather than bypassing the thing telling you there's a problem (looks like a standard thermistor+relay combo, so the only thing to watch out for is that you don't cycle the equipment on and off rapidly since the thermistors won't cool down and you'll lose the current-limiting). You can get DIN-rail-mount ones that address multiple hard-start loads being connected if that's what's causing it.

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