RCD wiring into fuse box

[jrli2008]

Just need some clarification...

installing a 8kw electric shower, none previously fitted.

only has a older style fuse/trip box (1989 build)


In taking power from this fusebox, where should it come from and I was just going to install a separate RCD, but would I need a MCb too?

ta guys

 

[MDJ]

what make of board is it?

 

[telectrix]

first, is there a spare fuse/mcb space in the board. if so fit a 40A , then come off the L/N into RCD.

if you ain't got a spare way, then split the tails into henley blocks and fit a RCD and MCB.

 

[rattlehead85]

You would need 10mm2 cable with a 40a protective device in your board. You can either run the circuit through a separate 40A RCD unit or if you have a modern type board with 60898 mcb's you could either install a 40A RCBO or place the circuit onto a designated RCD protected way inside your board. Plenty of options to look at.

 

[jrli2008]

Great, this is all mega helpful.

Let me get some pics up to just clarify things.

- - - Updated - - -

first, is there a spare fuse/mcb space in the board. if so fit a 40A , then come off the L/N into RCD.

if you ain't got a spare way, then split the tails into henley blocks and fit a RCD and MCB.

i think there is space....check piccy when I done me post allotment...

 

[jrli2008]

space to me!

 

[telectrix]

6MM cable is adequate if not derated due to insulation and VD is < 5%.

 

[rattlehead85]

space to me!

OK you will need to install a type 1 40A MK MCB and install a separate 40 RCD unit next to board and run your 10mm2 cable through that. Word of warning though you might have difficulty getting hold of one of these MCB's now as they aren't made now as far as i know. Please do not try and adapt a modern type breaker to this board as the bus bar anchor is a slide screw in type which could lead to arcing issues especially from the shower load if not fitted correctly. If you can't get one you may need to do a board replacement or install a shower board unit and split the tails with a henley block back at source / intake position.

 

[Fin170]

The 32A RCBOs for those old MK boards come up on ebay regularly for a reasonable price, can't say I've seen many 40s around. E.g.

http://www.ebay.co.uk/itm/DIGITALLY...akers_RL&var=550198035029&hash=item3a7bf93526

That or as said above

 

[rattlehead85]

I stated 40A as the op didn't say the wiring method or routing to be taken so i have assumed worse case scenario. As above post says 32A may be adequate. I have had trouble getting these MCB's before. Ebay as mentioned could provide a solution.

 

[MDJ]

splitting the tails would mean adding a switch before both boards as one main switch is a requirement, okay haha we know it doesn't always happen, I'm just saying.

 

[jrli2008]

I stated 40A as the op didn't say the wiring method or routing to be taken so i have assumed worse case scenario. As above post says 32A may be adequate. I have had trouble getting these MCB's before. Ebay as mentioned could provide a solution.

this is all excellent feedback chaps...especially as it coincides with what I had in mind

Im running 10mm cable from wall, through to loft, via 40a isolation switch, then down and across under floorboards then down to ground floor.

Already got the RCD unit...ready to go next to the MCB unit.

so to confirm, 32a or 40a for the MCB?

 

[rattlehead85]

40A if on 10mm2 cable. If your putting an MCB in with the RCD unit you are obviously going for the tail split, Henley Option with 16mm2 tails. Do not put another MCB in the main consumer unit otherwise you will cause a discrimination issue.

 

[jrli2008]

So I cant put a MCB in the main CU and then run the RCD from that?

 

[telectrix]

yes you can. fit a 40A MCB in the CU, then come off that ( L ) and the neutral bar ( N ) to your RCD.