RCBO for elec\\\' shower

The Real Bash · Posted: Tue Mar 07, 2006 1:06 am Post Subject: RCBO for elec\\\' shower

Hello folks,
Need help in wiring-in above in cu. I want to set it up so that only the shower is governed by the rcbo. Can't make head nor tail of the wiring diagram that came with rcbo. There are 2 terminals on top and two on the bottom - any ideas? My best guess is...bottom terminal marked 2 - Live from main swith on cu. Botton terminal N - neutral from main supply. Top terminal 1 live to shower. Top terminal N neutral to shower. Am I going to fry/boil?

dingbat · Posted: Tue Mar 07, 2006 1:21 am Post Subject:

You sure you should be doing this?

Is this rcbo fed from a busbar? Is it to go in a consumer unit with other devices or is it on its own? Is it actually an RCBO, or is it an RCCB/RCD? That is, does it have overcurrent protection as well as residual current protection?

If you can post up a picture it might help.

The Real Bash · Posted: Tue Mar 07, 2006 9:49 am Post Subject:

Many thanks Dingbat for your quick response.

I appreciate your candour and concern.! The answer to your 1st question is NO!
However, I am not as green as I make out. I re-wired my house 25 years ago, including elec shower. Of course, no rcd's or rcbo's in those days and thankfully never any problems. I know my limitations and will not do this unless 100 per cent confident.

To answer your direct questions - I am sure that it has both forms of protection, i.e. MCB current overload function AND voltage drop - earth leak detection. (These are my layman's terms but you will know what I mean.)

I cannot send you a pic, but details from the box are as follows. Makers are Felten and Guilleaume. Trade name Moeller? Fl/LS kombischalter Disjuncture differential. RCBO Interruttore combinato. (How is your German, French and Italian) 40A B 30mA Type-AC 1p+N 6kA 921972133 FL7-40/1N/B/003-6 JP43C is stamped on the front of unit. The leaflet describes it as a Combined Residual Current Device FL4, FL7-6. I am assured by my source of 25 years that it is correct. He did mention the cable size, and I am happy with original 6 square over a run of approx 15 metres. Shower is a Triton T90 8.5 KW tank-fed. Separate (single-pole? will check) switch fitted in hot press 25 years ago.

Initially there was no space left on the DIN bar for this new unit so, I have removed one MCB from the DIN bar (and busbar) and re-wired that circuit through another MCB of same rating which serves downstairs lights.. The removed MCB only served house alarm (.5 Amp?) so no overload on 2nd MCB.

This unit does not line up with the present MCB's on DIN bar. The bottom is offset - i.e. it is recessed further into the cu - therefore I presume that it is not to be supplied from the busbar, but have its own supply from main switch? All the switches align when the cover is replaced on cu..

I don't want to overload you with too much info and I have probably left out something important. If I am right about the top 2 terminals, how do I supply a live and neutral to the bottom 2 in such a way that only the shower is going through RCBO. For now I don't want any other items going through it which may trip the device. If and when I get it going OK for a while I will most likely run kitchen sockets through it also. (These serve the garden)

Thanks again,
Look fwd to your reply,
Bash (That name was already taken - hence The Real Bash!)

sparktrician · Posted: Tue Mar 07, 2006 10:45 am Post Subject:

sounds like you should change your rcd, this one is designed to be mounted on a din rail and be feed via a common live and neutral bus bars,

you can buy an rcbo which should mount on your present bus bar, and has a neutral fly lead attached so it can be wired in to the common neutral bar lead, pop down your wholesalers and ask them, try and get same make for ease of installation.

JohnD · Posted: Tue Mar 07, 2006 10:53 am Post Subject:

Although an RCBO is an excellent device, if it doesn't readily fit your CU. you might be better served with a separate, RCD, adjacent to the CU, which interrupts the existing feed from the MCB in the CU to the shower. You will need an additional small enclosure. Some of the more modern RCDs (including MEM) have a thin white wire that goes to earth, I understand it improves the action of the RCD. Other don't have, and don't need it.

BTW depending on design, yours may fit with an insulated black neutral cable running to the "N" terminal at the bottomof the RCBO from the neutral block in the CU. You can fit this yourself. the "N" doesn't usually go into a busbar in a CU.

The "P" side should fit in the phase busbar.

Both the Black and Red load cables go into the top. But you would do better to have it fitted by someone who is familiar with the method.

See if you can get an illustration from your supplier, of an RCD in a CU. Some of the catalogues have good pics. I suppose in RoI you are allowed to DIY?

dingbat · Posted: Tue Mar 07, 2006 11:10 am Post Subject:

As TparkT says, you'd be better off with one that fits your existing consumer unit.

However, what you have is an RCBO, with residual current protection set at 30mA and overload protection of 40A Type B, which is (only just) acceptable for your cable provided that cable runs through no insulation, is not bunched with other cables and does not run through an area with a high ambient temperature. You do need to check insulation resistance and earth fault loop impedance on this circuit and externally to make sure the overload protection will operate correctly. You also need to be able to test the satisfactory operation of the RCD function.

You also must ensure your whole house earthing and equipotential bonding are up to current standards, and that supplementary bonding is present and correct in the room where the shower is.

If all this is in order (there are many, many posts on these subjects on this forum) the easiest way to proceed with the RCBO you already have is to buy a separate enclosure for it, and feed from the spare MCB-way. But of course, that will mean finding a suitably rated Type 1 MCB for your model of consumer unit. (I'm assuming you have BS:3871 MCBs). I would not advise attempting to cram the RCBO into your existing consumer unit, for several reasons.

No. Wait... You know what? Change your whole consumer unit for a modern split-load board. It will be hardly any more expensive than trying to use what you've got and it will be whole lot neater.

A board change is a notifiable job, but the shower installation is notifiable anyway, so whatever you do you must either inform building control and pay their fees or use a registered electrician. And the more I think about your circumstances the more I am convinced you should get a man in.

dingbat · Posted: Tue Mar 07, 2006 11:13 am Post Subject:

And, of course, while I was checking my spelling John D got in first.

And he's right, Part P doesn't apply in Ireland.

I still think this job is beyond your knowledge and experience to do safely though.

The Real Bash · Posted: Wed Mar 08, 2006 12:27 am Post Subject:

Thanks to all for your good advice. I am going to do some more homework before (if I do) I post another ?

I think it may be a bridge too far for me. Fitting the unit and wiring it up does not put me off...I did get a separate unit to fit alongside the cu - but I would prefer it inside. Btw, the unit does fit on the din bar just as an mcb does. it's the testing procedure I am totally unfamiliar with and it's not something I want to get into. I thought that it was really only a matter of replacing 1 shower with another with a bit of tweaking of the wiring thrown in.

Thanks for all your help.

I may be back!