Division of circuits

[clark]

Been asked to change an old domino board for an RCD. Situation is it's a terraced house, currently the upstairs downstairs and kitchen sockets work off one fuse and all lighting in the house works off the second. My question is In order to comply with regs Do I have to have to have kitchen sockets on one mcb, downstairs on another lighting on two others and so on, it would seem a bit overkill as the house has been safe like this for years and all this extra wiring would make it very costly for the customer. How would you more experienced guys divide this one up? Any help really appreciated.

 

[Octopus]

Go with a small board with RCBO's. Will meet the requirements. Anything else would be completely OTT.

Don't forget to review the tails and bonding and where appropriate change

 

[IQ Electrical]

You have no obligation to alter the existing configuration.

Make a note in the 'comments on existing installation' box if you wish.

If there are only 2 circuits then RCBO's will give you some division by way of a power fault not affecting the lighting circuit.

 

[telectrix]

agree. unless the client is prepared to divide the circuits, entailing a major rewiring job, go for RCBOs

 

[clark]

2 rcbo's on a small board plus tails and earth upgrade then. Are we all agreed?

 

[Octopus]

2 rcbo's on a small board plus tails and earth upgrade then. Are we all agreed?

Are you Clark or Clarkster?

 

[malcolmsanford]

Just a point on the tails, I'm sure you have no intention of opening the meter in order to change these tails ? So you could fit the old tails into a Henley block/Isolator and then run the upgarde tails from the block to the CU. Or depending on the size of the existing tails leave alone as there is only 2 circuits.

 

[telectrix]

have you opened the existing DB to see if more than 1 circuit has been stuffed into 1 fuse?

 

[andekoch]

I was just about to say what telectrix said. Often there is more than one circuit put into a single fuse. In which case it is easy to get more discrimination. In any case a small board with rcbo's is the answer.

 

[Spudnik]

Yep, i have seen two lighting circuits in one fuse, which does allow a bit of discrimination.

 

[nickblake]

just to add to what jason has said if there are more than one lighting circuit into the MCB you can split them but before you do test the 2 circuits for seperation as you may well have shared neutrals there

 

[BOROROBBO]

just to add to what jason has said if there are more than one lighting circuit into the MCB you can split them but before you do test the 2 circuits for seperation as you may well have shared neutrals there

beat me too it.

normally up and down lights when put on seperate RCBO's or on different sides of an RCD will end up tripping it because of borrowed neutrals. its probably more than likely with the age of the installation. its just something else to watch out for.

as for the tails upgrade... depending on what size they are but i believe its around 87 amps maximum once diversity has been worked out before you need to upgrade from 16mm to 25mm. (please someone correct me there if i am mistaken, its just 87 amps seems to stick in my mind)

 

[baldsparkies]

Just for the avoidance of doubt, and very much in the real world.
Should you find yourself in a position where a non rcd consumer unit is being changed for a dual RCD unit, and as is very often the case the landing light has borrowed the nuetral from the 1st floor but fed from the ground floor. You can either aproach the customer with a cost for rewiring the landing light (Then cover your ears)
Or place both lighting circuits into one mcb, and listing it in the comments as a departure, along with the reasons why, ie Issues regarding borrowed nuetrals.
Its a get you out of jail card, not perfect, but acceptable never the less.

 

[claire_r]

I just put the board in as it is and separate them on the rcds. Usually theres a couple of extra cables for a spur or os light that can go on their own mcb