Can't reset the RCD with any MCB's on - Faulty RCD?

[Geoff101]

Would a N E fault not keep the rcd tripped all the time? Why would it only trip when trying to reset and not once reset and why would switching the MCBs off then allow it to reset?
Not saying it wouldn’t I just need the thoeory explained to me....
Thanks

 

[littlespark]

When you reset the RCD with MCBS on, all the appliances you have plugged in are all trying to come on at the same time.
Have you tried unplugged everything and having the MCB's on when resetting?
Is it an RCD, or an RCBO/RCCB. And what is its current rating? (overload?) (photograph of consumer unit would help)
The combined load of everything starting up may be tripping the breaker side

 

[telectrix]

had this a few times on older installations.1 or 2. 2 MCBs on, RCD would not reset. all MCBs off, reset RCD, turn MCBs on 1 at a time.

 

[Geoff101]

When you reset the RCD with MCBS on, all the appliances you have plugged in are all trying to come on at the same time.
Have you tried unplugged everything and having the MCB's on when resetting?
Is it an RCD, or an RCBO/RCCB. And what is its current rating? (overload?) (photograph of consumer unit would help)
The combined load of everything starting up may be tripping the breaker side

Yes but some circuits are lighting circuits with the lights all off, the oven circuit just had an oven on which surely shouldn’t trigger it one it’s own otherwise everyone would have the problem.
It’s an MK rcd 7880s. 80a 30ma.

 

[markythesparky]

What was there before the new rcd was fitted? Was it a straight forward main switch?

 

[Deleted member 9648]

I've come across the problem a few times over the years where the RCD (If I recall always a 4293 not a 61008) will only reset with all mcb's off. My recollection is it has invariably been a N-E fault, I cant remember having to change an RCD to rectify the problem. That said it's been a while and my memories not what it was......

 

[Geoff101]

No, it used to have an rcd but I think it was changed when the work was done. Could it have had a wider rcd which was changed for a narrower one to open up more ways on the board?
I recall we needed addional ways and I think this is how it might have been achieved without changing the cu. make sense or not?

 

[Geoff101]

No, it used to have an rcd but I think it was changed when the work was done. Could it have had a wider rcd which was changed for a narrower one to open up more ways on the board?
I recall we needed addional ways and I think this is how it might have been achieved without changing the cu. make sense or not?

 

[markythesparky]

Yes that’s possible with that fuseboard although if your electrician has changed that rcd, it doesn’t comply with regulations.

There are regulations regarding discrimination which your installation falls short of. He/ she should not have issues certs staying that it complies.

However, getting back to the troubles at hand, it may be prudent to unplug everything within the house, leave the mcb’s on and then try and reset the rcd just to see if it’s an appliance or a number of appliances causing the issue. The start up of a lot of things at once may cause an issue.

Just trying to narrow it down!

If you eliminate the impossible, then all that remains, however improbable, must be the truth!

 

[marconi]

Alas and alack, simply opening a single-pole mcb does not disconnect the neutral wiring. So, with any but only one mcb turned on and then closing the double pole RCD all the final circuits line and neutral circuitry are in play as far as electrons are concerned including current paths to earth and especially transient currents as these circuits are made live but not energised to full mains(240V) potential - apart from the circuit of the closed mcb.

My simple experiment would be to disconnect the L, N and cpc of the induction hob circuit at the CU ; it's my number one suspect for your problem because of its in-line power EMI filters and how they respond to transient voltages between L and N and L and E and N and E. Then, with all mcbs closed try re-energising the board - I suspect the problem will go away. Put the induction hob on its own rcbo. If not I think you will find a number of mcbs can now be closed and then energised. Final circuits which might give you a problem will have white goods, microwaves and some types of computer equipment which use the earth/cpc for EMI filtering purposes.

Herein lies a problem - the sole RCD is also the Main Switch. What needs to be arranged is a Main Switch which supplies the RCBO for IH and the RCD for all the remaining mcbs. I don't think you have room fit an a new Main Switch and an new RCBO unless one combines some final circuits. If it was me I would replace the CU with a Main Switch and dual RCD board plus RCBO for IH or plump for the top end aka Murdoch solution - Main Switch and all RCBOs for final circuits.

(Please take a photo of your cut out, earthing bar and meter arrangements so we can try and discover the earthing system in use.)