Rcd Test Switch and circuit not working

[WSB]

In my consumer unit I have a MK5780s 80A rcd protecting the ring circuit and lighting circuit in the utility room. It also protects the cooker in the kitchen.
All items on that rcd circuit no longer work.
Switching the rcd on makes no difference. Doesn't trip out, just doesn't work. Also, unlike my other rcds, the test button no longer trips the rcd.
Could it be that the rcd needs replacing?
Do these rcds often need replacing?
Thanks

 

[oldbutnotdead]

Are you sure it isn't in fault mode? On some RCDs the lever will stay in the ON position after tripping. Does switching it on feel the same as switching others on.
Unplug/disconnect all loads esp the oven, try again.
Turn power off to rcd, switch rcd off then on, restore power-does rcd make tripping noise when power is restored?
Def needs investigation. Often fail-no. Occasionally-yes

 

[JohnW2]

... All items on that rcd circuit no longer work. ... Switching the rcd on makes no difference. Doesn't trip out, just doesn't work. Also, unlike my other rcds, the test button no longer trips the rcd.

If the RCD didn't trip, and the test button does not cause it to trip, how did it come to be 'off' for you to need to reset it?

With some RCDs (and MCBs), you need to push the lever down firmly, as far as it will go, before you can push it up to reset it.

Kind Regards, John

 

[WSB]

Thsnks folks.
I have tried pulling the switch down before pulling up and compared with the other rcds.
For some reason it's not resetting when pulled up and test switch not working.
Switching it on feels the same as the other rcds.
Have tried switching the circuit breakers off that the rcd covers but even when these are all off, the rcd won't switch on and test switch doesn't work.

 

[JohnW2]

I have tried pulling the switch down before pulling up and compared with the other rcds.
For some reason it's not resetting when pulled up and test switch not working. Switching it on feels the same as the other rcds. Have tried switching the circuit breakers off that the rcd covers but even when these are all off, the rcd won't switch on and test switch doesn't work.

It could just be a dead RCD - you really need an electrician to investigate.

As I asked before, how did it come to need resetting (i.e. why was it 'off') - did something trip it, did you switch it off manually, or what?

Kind Regards, John

 

[oldbutnotdead]

You need to disconnect the loads. Switching MCBs off leaves neutral connected so any N-E fault will still be active.

 

[WSB]

The washing machine and cooker were on when it stopped working. My suspicion is with the cooker. About 6 months ago, it tripped when the cooker heater element blew. On that occasion it was resettable.
I changed the cooker heater element with a cheap one from ebay. All worked fine till now.
My suspicion is that this cheap heater element has blown causing the rcd to trip.
This time round though, I can't reset the rcd.
Do they have a limit to the number of times they can be reset?

 

[JohnW2]

You need to disconnect the loads. Switching MCBs off leaves neutral connected so any N-E fault will still be active.

That's true IF there is an N-E fault. That's why I've been trying to ascertain how/why the RCD came to be 'off'.

If all was working until, say, the OP switched it off manually, then it would be exceedingly improbable that an N-E fault had suddenly arisen at that very time (unless, I suppose, the OP switched it off to 'do some work' {not very correctly!} on one of the protected circuits!!).

Kind Regards, John

 

[WSB]

Have all appliances switched off plus each of the circuit breakers for the circuit switched off too

 

[JohnW2]

The washing machine and cooker were on when it stopped working. My suspicion is with the cooker. About 6 months ago, it tripped when the cooker heater element blew. On that occasion it was resettable.

Thanks for clarifying.

In that case, as oldbutnotdead has said, you really need to totally disconnect the cooker (including its neutral) (and unplug the WM) and then see if the RCD will reset.

Kind Regards, John

 

[oldbutnotdead]

The washing machine and cooker were on when it stopped working. My suspicion is with the cooker. About 6 months ago, it tripped when the cooker heater element blew. On that occasion it was resettable.
I changed the cooker heater element with a cheap one from ebay. All worked fine till now.
My suspicion is that this cheap heater element has blown causing the rcd to trip.
This time round though, I can't reset the rcd.
Do they have a limit to the number of times they can be reset?

Ah ha.
No there's no intended limit, as with anything with moving parts, eventually something will wear out.
So, have you isolated cooker & w machine before trying to reset?

 

[WSB]

Yes, have switched off all devices and set all trip switches on the circuit to off.
When I switch rcd on it appears to go on OK then I switch trip switches and appliances on.
Rcd doesn't trip.
Just no power to anything and like I said, the test switch no longer works

 

[BS3036]

If you put a short circuit through an RCD, it has a good chance of dying. (From experience!)

 

[JohnW2]

Yes, have switched off all devices and set all trip switches on the circuit to off.

As has been said, that is not necessarily enough - you may need to actually disconnect the cable (both L and N) from the cooker, since its own switch(es) may not disconnect the neutral, and the associated trip switch certainly won't. With the WM, you may be able to simply unplug it - otherwise you'll have to do the same as with the cooker.

Kind Regards, John

 

[WSB]

I understand what you're saying with a neutral to earth short. Of course, the trip switches only switch out the live. So need to take the n-e fault or of the equation.
Will need to power all down and unwire the cooker properly before trying again.
Maybe the rcd isn't broken after all