Single Phase RCD Type C/Breaker

CB trips when more ampere flows through it. If CB is 40A and ampere flowing thru it is more. After some time CB will trip . This is thermal tripping. If you energise , it will work till the temperature rises to the tripping thermal temperature.

The solution is increase the ampere rating of CB. But take care the wire/cable capacity. If more current passes though you wire, it will burn.

<...The solution is increase the ampere rating of CB...>

The solution is to find out what has changed since the CB started tripping, and correct it!

Agreed. This could be as simple as a loose ground or neutral in the panel, or may not be the circuit at all, but a fault in one of the appliances that are hooked up to it. Boosting the CB rating is literally playing with fire.

If it is a residual current device, check that there is no path between earth and neutral downstream of it. If there is, then there is a fault downstream of it; rectify the fault, for that is what the device is indicating.

How many outgoing circuits are connected to the RCD/CB?. Megger each circuit and also measure current in each circuit when carrying load. When it trips if you can't switch on again switch off circuits one by one and isolate the fault.

Many years have passed since installation of this single phase breaker. To remedy the problem, replace the breaker, with a similar one. Over time, the bi-metal strip will weaken causing it to trip. Also over time the load on that circuit may have been increased. The breaker is there to protect the circuit from over voltage and high amperage draw usually causing a high heat in the wiring. Double check the usage and replace the breaker.

Just to confirm these devices do not protect against over voltage, they only detect current It's possible that the RCD side is failing or indeed there is actually a fault on the circuit. I would change the device and rule that out first

The key to this is, the OP said water pump. I would start checking there first. If the breaker is tripping thermally, the pump must be drawing excessive current. Not enough to trip instantly, but enough to cause the breaker to heat up. If it is an RCD, then the motor may have an insulation problem. Just my 2cents.

If the pump tripped on a short circuit it would trip the breaker and show over. For it to take its time it would suggest its pulling about 50 or 60 amps. I don't know whether we are 110V or 230V but even at 110V its some mother of a pump to be running in a domestic environment. A simple ammeter tong test over wiring will sort this and take it out of the equation.

You have virtually eliminated the possibility of a faulty breaker by swapping it.

Its possible the pump is breaking down. Is it double insulated - many are. If it is it won't have an earth path back.

My bet is a failing cable.

Use a fluke clamp meter with min/max amp reading.

I had the same problem with a hot tub I was called in to fix. It was a very expensive circuit breaker...a two hundred dollar dual phase GFI. Same symptoms exactly. We also changed the GFI, and the symptoms did not go away.

The fix was...clean and dry the pump area. Install ventilation.

It was stray leakage current which was the problem.

A similar problem on the airplane I was told to fix turned out to be a wire in a wire bundle which was chaffing. I figured it out suddenly when I discovered that the breaker would trip every time a technician walked to the back...flexing the underfloor wire bundle. A real bxxxxx to find, but easy to fix once we found it.

Two possibilities. I bet there are more.

Well dont know if theres much left to say. Except I would like to think the wire should be ok being only 9yrs old, check anyways. I maintain a sWmill that still has rubber and paper insulated wires in the office area and still ohms 100+ megohms. Breaker maybe weak, check with another circut. And I personally think the water pump probably has bearings going bad to cause the thermal trips or could be something restricting the flow of water causing back pressure, assuming the pump doesnt hVe a relief on it I would think so since its a 110v pump(sounds to cheap to hVe one) thats just what the maint. man in me is thinking. Oh and since u changed the breaker and its still doing it I say pump.

MR. Thobias,

Did you solved it ?

Not yet sir,because I was out of city.But I hope from all these directed instructions I will rectify it.Thax very much u all .