Dear all I'm about to install a 9.5kw shower. From looking at other posts on this forum I understand I need to use 10mm cable and a 45 Amp isolator switch (which I'm going to put outside the bathroom). I, amazingly, am lucky enough to have two spare slots in my Wylex consumer unit (which is about 8 years old and does not have an RCD). I think I'm right in saying that the regs dont force me to use a RCD/RCBO, but obviously this would be good practice. Can someone point me to the best option for my consumer unit (I presume I need to use Wlyex and cant get away with another brand in their consumer unit?). Should I go RCBO? and if so what rating? Would an RCD need an MCB as well, and hence take up three slots? Ideally I'll be able to find a solution which I can buy from screwfix. Thanks for all your help in advance Ben
Hi Plugwash Unfortunately I dont know. I can take a look tonight - is it easy to tell? Any chance you could suggest a solution for each possibility so I can get my order in tonight at home? Thanks for the quick response.
Have a look at the following link, it should give you an idea of what you have. http://www.tlc-direct.co.uk/perl/search.pl?search=wylex
The fact that you don't know what rating of MCB or RCBO to use, and the fact that you don't realise that an RCD won't provide over-current protection makes me wonder if you are fully equipped to undertake this task....
Thanks for the concern. I'm pretty happy with the P=VI, V=IR equations. On a P=VI basis I'll be using just under 40 Amps. I presume a 45 Amp fuse rating will suffice. Agreed, stupid question re MCB + RCD. If I'm in any doubt I'll get a qualified sparky to come round and check it out before i flick the switch. I think I have the plug in type Wlyex MCBs - I couldnt find a plug in RCBO - whats my best bet?
If you have plug-in MCBs, RCBOs are not available for your CU. I think Wylex only manufacture fuses/plug-in MCBs upto 40A rating - check. If you find a suitable fuse, fit an RCD fed from this, feeding the shower. If you need more than 40A and such fuses are not avaiable, you will have to wire a shower CU (1 or 2 way CU with RCD) with a suitable MCB, into the meter tails. Don't try this unless you're totally confident! Jon.
if *AND ONLY* if the cu has a 100A incomer you can fit a 45A cartridge fuse with an RCD downstream there are some earth fault disconnect time issues with a 45A cartridge but the rcd downstream should cover this but frankly i think its best to have the CU replaced that way you can give rcd protection to sockets as well
they do actually they are called GE mini trips (i keep forgetting about them) toolstation do them they do seem a little pricey though (note that unlike wylex breakers bases for minitrips are sold seperately) http://www.toolstation.com/shop/Electrical/CircuitProtection/d190/sd2615?QuickAdd=44250&department=190&subdepartment=2615
Dear all Embarrasingly, I've now slipped off the front cover of the consumer unit and found that I have the non plug-in type! I've looked to see what I can buy on the screwfix catalogue at there are type A and type B "clip in" (my phrase) MCBs and a vartiety of RCBOs. There also doesnt appear to be a 45 Amp RCBO. Is my best bet to go for a 50 Amp 30 ma RCBO? It seems that I shouldnt just stick to a 50Amp MCB (just out of interest, what's the difference between type A and type B?) - is this right? Thanks again for all your (collective) help. I'd be stuck without you.
Wylex don't make 45A MCBs or RCBOs, so you will need a 50A. And it'll have to be an MCB with an external RCD fitted, as their RCBOs are all Type C, which are not to be recommended for a shower. See http://www.electrium.co.uk/downloadfile.asp?Type=C&Company=8&Id=1 for full details of Wylex products. The difference between Type B, C etc MCBs is basically how quickly they trip at what level f overcurrent. See here: http://www.tlc-direct.co.uk/Book/3.6.4.htm for a quick explanation. BTW - Type A MCBs in your CU? I'd be surprised....
Thanks for this info. Looks like I must have type B then. The reason I wanted to use an RCBO is because I have only got two slots, and an RCD + MCB would take three slots. I'd really rather not put in a seperate shower consumer unit - can I make another brand fit? Are there any other options? Thanks again for the help.
Hi, Here's how to do it. From what I've read so far, you have an old-style Wylex rewirable fused consumer unit? OK - You should be able to get a Wylex 45A type B mcb to retro-fit into one spare way. Use this to feed a shower protection unit with some 10.00mm twin and earth. Live from the mcb, neutral from the neutral bar in the CU. Connect the other ends in to the shower protection unit. Screwfix do one but its not a well-known brand. Contactum do one though, which is fine if a little pricey. In the shower protection unit - basically a 4 way plastic enclosure with a bit of DIN rail inside it, you fit your double pole 30ma RCD. Again, Contactum do one. Feed your double pole shower switch via some 10.00mm from the outgoung side of the RCD. Finally, run some 6.00mm single earth cable from the shower to the shower protection unit to bond up the installation. I may have missed a few bits here and there but you get the genaral idea. Plus - you only use up ONE spare way in your CU. Hope this helps. TT
why do you need to run a separate 6mm earth wire Usual regulatory Bonding requiements apply. As I said, I might have missed a couple of things, one of these is the method of bonding. Shower should be bonded to class 1 equipment and to pipework in Bathroom. See 1EE On site guide and BS7671 for further info - failing this get a sparks in. TT
OK I just spoke to the Wylex technical people to see if they had any more ideas - hopeless bunch - wasnt worth the 10 minute wait on the phone. I'll go for a 50amp type b mcb. If I want RCD protection, it seems like i need a separate unit, unless I can get another brand to fit. Am I right in saying I just come out of my MCB and then go into a separate unit which provides my RCD protection? Would the "wylex shower protection unit" on screwfix do the job? I'm mounting my isolator switch for the shower in a place which is out of the way - could I put this "shower protection unit" next to the isolator switch rather than the consumer unit? Thanks again for the help
The RCD in it's din rail box, ought really to be fitted next to the main fusebox, so that the whole length of shower circuit cable is protected. And Yes - Good earth bonding is Vital in ANY equipment where water and electricity are in close association, such as immersion heaters and showers and bathroom electrics.
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