RCD keeps tripping

[lee p]

I have a problem with an MK Sentry split load board that I'd like to share...

When I connect the earth from the supply head into the earth terminal from which I have fed the consumer unit with, the RCD trips.

I have checked every socket on the RCD side of the board for any faults - there are none.

If the earth is disconnected from the board then the RCD operates - no problem, but once the board earth is linked to the supply head earth it trips even when there are no circuits in operation i.e. all MCBS even those on the main incoming are switched to the off position.

The board is configured in such a way so that the tails from the meter come into the board and enter the main switch at the top.

On the left side (bottom) a tail then feeds the neutral bar.

The right side (bottom) is attached to the busbar and has MCBS for lighting circuits, boiler and smokes.

There is a link from the neutral bar (main side) to the top left terminal of the RCD then a link left bottom to the split neutral bar.

There are no obvious connections in the board (like neutrals on the wrong side of the RCD, MAIN SWITCH so I am stumped....

All suggestions appreciated

Lee.

 

[davy_owen_88]

What are your insulation resistance results?

 

[bernardgreen]

The right side (bottom) <<of main switch>> is attached to the busbar and has MCBS for lighting circuits, boiler and smokes.

There is a link from the neutral bar (main side) to the top left terminal of the RCD then a link left bottom to the split neutral bar.

Where does the bus bar from main switch right enter the RCD ?

If it links from right hand side of main switch then it has to enter the RCD on the left side of the RCD but you say the Neutral it taken to the upper left of the RCD.

If the bus bar is connected to the lower left the neutral to the top left then you have a short between live and neutral.

Who installed and wired this consumer unit ? It sounds like the person who did it has no idea of how to wire split consumer unit.

Turn the power off. Reconnect the earth to provide some safety and call in an electrician.

 

[davy_owen_88]

I'm assuming you bought it in split load config so it is going to be wired correctly. I'll find a picture of one of RF's Sentry installs for you to see ASAP.

Neutrals should be like this:

Meter tails > main switch (top left)
main switch (bottom left) > neutral block
neutral block > RCD (top left)
RCD (bottom left) > RCD neutral busbar.

Lives:

Meter tails > main switch (top right)
main switch (bottom right) > busbar and linked to RCD (top right)

If this is correct then what are you IR readings.

EDIT:

Heres an MK Sentry wired by RF Lighting: (look how pretty it is )

 

[lee p]

Bernard,

Davy Owen has kindly supplied a picture and that is exactly how my board looks mirror image.

DAVY thanks and yes it was supplied pre-configured all that was required was to cut the busbar to size.

I installed it a couple of days ago, and am qualified to do so, may be my explanation of the connections was poor, admittedly I don't do the job full time as I keep the peace full time if you get my drift.

I have done all the main and supplementary bonding but when I link the earth from the supply head the RCD trips, I always have someone come in and test and inspect my work once completed but was hoping to resolve this beforehand.

If the main switch and RCD are switched on with no other MCBS in operation the RCD trips when the earth is connected?? If however the earth is disconnected the board operates without disconnection

 

[BJS_Spark]

I would firstly put the earth in place and leave it there as this is a safety requirement and connecting and disconnecting it like that is a very bad idea.
You then need to remove all the neutral wires from the final circuits and test that the RCD resets. Then reconnect the neutral's one at a time and see if you have a final circuit fault such as a neutral earth short.

 

[bernardgreen]

YES I know the LIVE feed to the RCD should not come from the bus bar but via the tail as shown in the photo.


But having seen a DIY CU intallation ( cheap skate land lord ) where the bus did feed the RCD to make a live neutral short through the RCD it is possible. The RCD would trip immediately power was turned on.

 

[BJS_Spark]

Of course you could do an IR test on the final circuits but one would assume you had already done that before connecting them up?

 

[davy_owen_88]

Get in someone who can test your installation. Did you do a complete rewire or just a CU change?

Oh and thank RF and his massively overworked camera for that picture

 

[lee p]

Bernard

Thats the thing it trips only when the earth from the supply head is connected into the main earth terminal, otherwise the board functions ok, I appreciate everyones concerns about there being no earth, hence my reasons for wanting to resolve the problems ASAP, fortunately house owners are away.

So all ideas welcome

BJS I will do as you suggest, has anyone else had a similar problem
I'm asking the questions by virtue of the fact that I want to learn from this

 

[securespark]

I'm a little perplexed here: you say you are qualified to change the CU, yet cannot produce test results. Also, your understanding of the situation is a little lacking.

FIRST OF ALL, RECONNECT THE MAIN EARTHING CONDUCTOR

& DO NOT DISCONNECT IT AGAIN!

You have an earth fault. There are two types: P/E & N/E.

The first would clear if you power down the MCB. Hence you have a N/E fault.

You say the sockets are OK. How have you checked them?

You need to disconnect each circuit in turn & try and reset the RCD after each one is disconnected. When you get to the point where the RCD resets, that is the faulty circuit.

Make sure you have not connected any of the neutrals to the wrong busbar.

If you have not connected up wrong, then I assume there is a N/E short on the faulty circuit. You need to meg the cables to see what the IR is.

You have got the kit??

 

[davy_owen_88]

Sorry Lee, but I have to question what you think makes you 'qualified' to do this work. If you can't (and don't test) test the installation then how do you comply with BS7671? You obviously aren't a member of a self cert. scheme and since this work is notifiable I'm curious to know if you have notified your BCO and paid the fee?

 

[bernardgreen]

Bernard

Thats the thing it trips only when the earth from the supply head is connected into the main earth terminal, otherwise the board functions ok

Which means that there is a fault to earth. And that means if the earth connection is not there then ALL the electrically earthed items in the house are connected through the fault to either live or neutral.

Without the earth connetion there is no route for current from the fault so the trip doesn't trip. But all exposed metal connected to the electrical earth is at a potential determinced by the type of fault and could be anywhere between neutral and live. Thats pipe work, cooker, any metal lamp or tool plugged into a socket.

You replaced the CU. How did you isolate the tails....

 

[lee p]

SECURESPARK

I am not part P certified hence I have someone I use to certify my work.

I realise from your comments that the fault exists as a NE fault, because switching the MCBS off only cuts the phase.

 

[DESL]

I am not part P certified hence I have someone I use to certify my work.

Hmmm how come you didn't spot the fault when doing IR tests?

Borrowed neutral somewhere?

Or neutrals crossed behind the DIN Rail - we have all done it on MK sentry CUs