New consumer unit - now no electric

BarelySentientAI

Risteard said:

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

More likely a borrowed neutral. However this DB isn't even labelled. The alteration to the electrical installation should have been inspected and tested before being put into service. It would appear that this didn't happen!

That's a good shout actually, I didn't consider a borrowed neutral.

Not a good example of workmanship.  No competent electrician should have left it in that state, even if there were problems getting to some of the accessories.

Section62

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

Could possibly be a neutral-earth short on the left-half circuits.  E.g. Just enough for a path through the neutral side of the left RCD to generate sufficient trip current.  The 30 seconds delay in tripping might suggest a different cause though.

Best left to a proper electrician to sort out.

It isn't uncommon to find mouse damage to cables in a home where hoarding is taking place.

BarelySentientAI

Section62 said:

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

Could possibly be a neutral-earth short on the left-half circuits.  E.g. Just enough for a path through the neutral side of the left RCD to generate sufficient trip current.  The 30 seconds delay in tripping might suggest a different cause though.

Best left to a proper electrician to sort out.

It isn't uncommon to find mouse damage to cables in a home where hoarding is taking place.

Would a neutral-earth fault on dead circuits trip anything?  I wouldn't expect there to be any current.

It's nothing we can diagnose online given the simple checks don't work though - on-site electrician is certainly needed.

Risteard

BarelySentientAI said:

Section62 said:

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

Could possibly be a neutral-earth short on the left-half circuits.  E.g. Just enough for a path through the neutral side of the left RCD to generate sufficient trip current.  The 30 seconds delay in tripping might suggest a different cause though.

Best left to a proper electrician to sort out.

It isn't uncommon to find mouse damage to cables in a home where hoarding is taking place.

Would a neutral-earth fault on dead circuits trip anything?  I wouldn't expect there to be any current.

It's nothing we can diagnose online given the simple checks don't work though - on-site electrician is certainly needed.

If any of the circuits protected by that RCCB is energised then it won't take much load to create a sufficient imbalance to cause the RCCB to operate. That is why turning the circuit breakers one by one could just mislead as to where the fault lies. It could be on any of the protected circuits.

Definitely a (competent) Electrician is required.

Mr.Generous

BarelySentientAI said:

Section62 said:

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

Could possibly be a neutral-earth short on the left-half circuits.  E.g. Just enough for a path through the neutral side of the left RCD to generate sufficient trip current.  The 30 seconds delay in tripping might suggest a different cause though.

Best left to a proper electrician to sort out.

It isn't uncommon to find mouse damage to cables in a home where hoarding is taking place.

Would a neutral-earth fault on dead circuits trip anything?  I wouldn't expect there to be any current.

It's nothing we can diagnose online given the simple checks don't work though - on-site electrician is certainly needed.

Yes an earth / neutral short does trip the board on most occasions. Old lighting circuits are sometimes wired with single strand cables, and as Risteard said because they are just running a live they often borrow or combine neutrals. Earths may not even be present. The new board measures current out and back from each breaker, as soon as the current goes out one way and back another it trips. Induced current (sometimes called ghost current / phantom voltage etc) can be enough to trip a board where the wiring is mixed.

BarelySentientAI

Mr.Generous said:

BarelySentientAI said:

Section62 said:

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

Could possibly be a neutral-earth short on the left-half circuits.  E.g. Just enough for a path through the neutral side of the left RCD to generate sufficient trip current.  The 30 seconds delay in tripping might suggest a different cause though.

Best left to a proper electrician to sort out.

It isn't uncommon to find mouse damage to cables in a home where hoarding is taking place.

Would a neutral-earth fault on dead circuits trip anything?  I wouldn't expect there to be any current.

It's nothing we can diagnose online given the simple checks don't work though - on-site electrician is certainly needed.

Yes an earth / neutral short does trip the board on most occasions. Old lighting circuits are sometimes wired with single strand cables, and as Risteard said because they are just running a live they often borrow or combine neutrals. Earths may not even be present. The new board measures current out and back from each breaker, as soon as the current goes out one way and back another it trips. Induced current (sometimes called ghost current / phantom voltage etc) can be enough to trip a board where the wiring is mixed.

Does it?  Looks a lot like MCBs with a single RCD protecting each half of the split bus.  That doesn't measure current out and back from each breaker, that measures the total current out and back through all the breakers on that half at once.

And I said "on dead circuits".  You've explained how a board populated with RCBOs operates on live circuits.  I don't think this is one of those.

Tripping for a fault on a completely de-energised circuit would be contrary to basic protection principles.

Borrowing a neutral from one of the circuits on the other half of the board could make sense though.  Especially given that the old board also had an RCD but not for the lighting circuits, and didn't have the problem.

All just speculation anyway.

ROY47

BarelySentientAI said:

colin25710 said:

BarelySentientAI
 Turned off 5 left hand switches - turned the yellow switch on and it immediately turns itself off again

Now that's very strange.  With all the ones to the left of it turned off, there should be nothing supplied through the yellow one and nothing to trip it.

That almost suggests there's a fault inside the consumer unit itself - possible but unusual.

More  likely a previous earth fault or neutral to earth  on the old 4 way consumer unit didn't have proper trip cover

as they said below ...

Pic of old and new setups - on the old the lights were on the old fuses  .. no trip protection

New consumer unit has correct trip protection

Home  serve are covering themselves by saying they need to access all the fittings in the property

Can imagine headlines   if something went pear shaped  at the property

FreeBear

ROY47 said: Home  serve are covering themselves by saying they need to access all the fittings in the property 

If it is a case of rodent damage on a cable, they may need to lift floorboards. That could complicate matters considerably.

Section62

BarelySentientAI said:

Yes an earth / neutral short does trip the board on most occasions. Old lighting circuits are sometimes wired with single strand cables, and as Risteard said because they are just running a live they often borrow or combine neutrals. Earths may not even be present. The new board measures current out and back from each breaker, as soon as the current goes out one way and back another it trips. Induced current (sometimes called ghost current / phantom voltage etc) can be enough to trip a board where the wiring is mixed.

Does it?  Looks a lot like MCBs with a single RCD protecting each half of the split bus.  That doesn't measure current out and back from each breaker, that measures the total current out and back through all the breakers on that half at once.

And I said "on dead circuits".  You've explained how a board populated with RCBOs operates on live circuits.  I don't think this is one of those.

Tripping for a fault on a completely de-energised circuit would be contrary to basic protection principles.

If the RCD is 'on' then the neutral side of the circuits is connected to the supply (or 'live', hence some electricians don't like the use of 'live' to refer generally to the brown wires).

In a split load board the neutrals (should) be commoned, which means the circuits on the half of the board with all the MCB's off will have their neutrals at some potential above zero (e.g. earth) which would be determined by the load on the other half of the board and the resistance between the consumer unit neutral common point and supply earth.  If that potential is enough, and the neutral-earth short gives sufficiently low resistance, a current will flow through the neutral coil of the 'off'-side RCD and then through to 'earth', and if that current reaches the RCD trip level the the RCD will trip out, even though all the MCB's on that side are 'off'.

Although it can be an annoying behaviour (e.g. tripping everything when you accidentally create a neutral-earth short when working on a circuit de-energised on the MBC only) I'd suggest it is the correct response in terms of basic protection principles.  If something has gone wrong on a circuit which allows current to flow neutral-earth then it is better to trip the supply at the RCD rather than have an ongoing situation where stray currents are pinging around the installation's earthing arrangements.

BarelySentientAI said:

All just speculation anyway.

Agreed.  There's a fault in the system which needs the right testing equipment and methods to pin down.

BarelySentientAI

Section62 said:

Although it can be an annoying behaviour (e.g. tripping everything when you accidentally create a neutral-earth short when working on a circuit de-energised on the MBC only) I'd suggest it is the correct response in terms of basic protection principles.  .

Given that one of the basic requirements of protection is to trip off only the smallest amount of equipment or circuits to isolate the fault, whilst leaving all other supplies undisturbed - I'd say tripping half a board for 'some fault somewhere, even when the lives are out' isn't great.

This could be one of those differences between my experience (HV system protection design) and domestic wiring though.