Safe T Cut tripping out

[graeme72]

Hello,

        My Safe T Cut RCBO just started tripping out even with all circuits switched off. Its normally set at 10mA but at 30mA its the same. All suggestions appreciated. Could a rat attack cause it?

[OneMoreFarang]

Option 1: There is still some connection somewhere which motivates it to disconnect.

Option 2: It's broken and you better buy a new one and have it professionally installed. 

[lopburi3]

And yes a rat attack can destroy just about anything.

[bankruatsteve]

3 hours ago, graeme72 said:

My Safe T Cut RCBO just started tripping out even with all circuits switched off.

Does it trip immediately or after a while?  Are there any meters attached (like a watt meter?)

[graeme72]

On 5/6/2022 at 2:23 PM, bankruatsteve said:

Does it trip immediately or after a while?  Are there any meters attached (like a watt meter?)

It trips immediately, no meters. Power goes to a circuit breaker with unprotected circuits (pump and hot water-own earths) then to the RCBO circuits. Has been working well for 12 or so years. I tried a new module, same result.

[lopburi3]

2 minutes ago, graeme72 said:

It trips immediately, no meters. Power goes to a circuit breaker with unprotected circuits (pump and hot water-own earths) then to the RCBO circuits. Has been working well for 12 or so years. I tried a new module, same result.

I may have misunderstood but having an earth does not replace having RCBO - different things.  As for the immediate problem I would also be unplugging everything (not just turning breakers off) as a double check (can't hurt and always a chance of getting lucky).  As for pump and hot water they are normally on RCBO - only emergency lighting and perhaps refrigerators are often wired to avoid here.

[Crossy]

Tripping with all the branch MCBs off?

 

Look for a N-E fault, damp or bugs in an outlet somewhere possibly.

 

You could start by disconnecting all the neutrals from your neutral bar (all breakers off) then connect them one at a time until you get a trip. Then investigate that circuit.

 

If it still trips with all the neutrals isolated then time to start posting photos of the distribution board wiring.

 

I'm assuming there have been no recent wiring changes of course.

[graeme72]

On 5/8/2022 at 11:17 AM, Crossy said:

Tripping with all the branch MCBs off?

 

Look for a N-E fault, damp or bugs in an outlet somewhere possibly.

 

You could start by disconnecting all the neutrals from your neutral bar (all breakers off) then connect them one at a time until you get a trip. Then investigate that circuit.

 

If it still trips with all the neutrals isolated then time to start posting photos of the distribution board wiring.

 

I'm assuming there have been no recent wiring changes of course.

 Yes, tripping with all the breakers off, no wiring changes. I disconnected all the neutrals, still tripping, so I disconnected all the earths, (with neutrals connected) still tripping, then disconnected N-E link, still tripping, and tripping instantly. Photo of the boards attached. 

[Crossy]

OK, all MCBs off, remove the link between the RCD N out and the N bar immediately above, this should isolate the RCD completely - still trip? If it does I think you have a defective unit, which bit did you replace??

 

If it's ok try with earths off and neutrals off connecting one N at a time until it trips.

 

Dumb question, is the "Test" button stuck??

 

EDIT Whilst all the neutrals are off the N bar check that it is isolated from the box.

[worgeordie]

That's the problem with Thai electricity been different .......????

not easy to find solution.

regards Worgeordie

[bankruatsteve]

Stupid question I suppose... The photo shows the RCBO not tripped. So, it trips instantly when the main breaker is turned on?

[graeme72]

On 5/10/2022 at 7:53 AM, Crossy said:

OK, all MCBs off, remove the link between the RCD N out and the N bar immediately above, this should isolate the RCD completely - still trip? If it does I think you have a defective unit, which bit did you replace??

 

If it's ok try with earths off and neutrals off connecting one N at a time until it trips.

 

Dumb question, is the "Test" button stuck??

 

EDIT Whilst all the neutrals are off the N bar check that it is isolated from the box.

Initially I only replaced the removeable module with the sensitivity selector, now I have changed the whole unit. I am using four circuits (MCB's). With the RCB N disconnected and the original RCB installed all four MCB's are tripping it, with the new RCB the three with the highest loads trip it instantly and the lightly loaded one trips intermittently. N bar is isolated and test buttons are free. (Not a dumb question).

[graeme72]

On 5/10/2022 at 8:35 AM, bankruatsteve said:

Stupid question I suppose... The photo shows the RCBO not tripped. So, it trips instantly when the main breaker is turned on?

Yes.

[graeme72]

For those who may be interested I have found the problem. After tracing wires, opening power points and junction boxes, I discovered a rat attack in an old style fluorescent light that rarely gets used. The insulation was 90% removed from all the wires inside the box. I need a levitating cat, unfortunately mine hasn't quite mastered that ability despite numerous attempts.