Options for new shower circuit

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Hi guys, would appreciate some comments on what others would consider best option in the following circumstance.....

Customer wants a shower circuit running from existing CU.......the circuit itself isnt the problem, its how best to suplly it. Currently installed is an old (80's??) wylex metalclad CU with the pushbutton 3871 mcb's in (yuk) and with a 63A RCCB main switch upfront of it all.

I did think about installing one of those push-in 50A Wylex 60898 mcb's in it for the new circuit but my concerns would be that im getting close to the 63A rating of the RCCB considering that there is a 40A cooker circuit and a couple of rings already existing. Id be worried the RCCB might not even still meet trip times aswell (how reliable were these type after years?) and really this board is well out of date but the customer is typical 'as cheap as possible' so changing the entire CU is a last resort thing to them.

Other option would be split the tails and install a seperate shower CU with its own RCD and breaker in it but to me this seems like dead money when a new CU would sort the lot.

Regards
 
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It would be first wise to test the existing RCCB and see if it complies to tripping times.
If it does not the answer is a simple one, replace it for a 100A rated one.
 
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I did wonder about the supply fuse size but luckily there is a Rec isolator after the meter so i wouldnt have to pull it, appreciatively that doesnt help if the additional load was too much for it. A 60A fuse would 'protect' the RCCB but id be worried if it blew one day and a network guy just came out and threw a 100A in. Interestingly i saw a 40A one the other week which was quite happy with a full CU running off it, 3 bedroom house with shower, cooker, etc.

Any idea what age these push button reset wylex breakers are anyone? 80's?

Not sure if using the existing board is a good idea but dont want to insist on CU change if it loses the job (unless that CU change is totally necesary of course). Worst part of our job this.....judgement calls!

regards
 
If you mean the plug in ones, they are still available (not 3871 but you can change them for new if you want).
Nothing wrong with the board.

You say a 50A for the shower.
Can you not limit them to a 9.5kW - 40A?

You could then change the cooker to 32A.

It doesn't make any difference really what the breakers are.
The current drawn will be the same, but you seem concerned with the numbers.
 
yeah ive used the 60898 new plug in ones plenty of times.

Customer has already bought a 10.5Kw shower :LOL:.

A couple of years ago i got called to a CU that was smoking and smelling. The 63A main switch was burnt up which looked like it started internally (not a loose tails connection) which i put it down to overloading over time as the CU was running a big house. Cutout fuse was 80A. I know we can apply a bit of common sense and more or less forget about the main switches/rcd's not exceeding their total rated load but i always pay closer attention when i see a 63A upfront device as in todays modern houses its a bit more of a realistic occurence than it used to be.

regards.
 
It may be best to find out what the fuse is and uprate if possible and then split the tails to a separate shower CU.

That way you are not altering the existing board.
 
It is a hard thing to tell a customer no I will not do that, and it is also hard to excuse yourself when things go wrong.

In theory the DNO should not fit an 80A fuse when there is a 63A RCCD and also no electrician should fit a 63A RCCD when there is a 80A fuse, so in theory you could say not my fault it some one before you get there has made an error, however in practice it would come back to you.

If it was your own house maybe you would take a chance, but with some one else's house then just not worth it, do it right or don't do it. Only safe way would to be to pull the DNO fuse and check on it's size, or email the DNO and ask them, needs to be in writing, phone call not really good enough. Fact you ask means you really know the answer.
 
A lot of them boards dont allow you to fit 2 high rated mcbs anyway, without bodging the back base which is not acceptable.
Not sure if 40amp was included
 
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Yeah, Wylex Standard boards with a sub-100A main switch were never intended to supply any device above 30/32A.

To try and guard against this, devices of a higher rating had a "key" moulded on the back of the fuse shield which did not allow it to sit flush.

People just snapped them off, though.

Never saw a plug in device higher than 45A, though.
 
@industryspark you are going to need 10mm² cable in any case, for that monster shower
You are going to need the circuit to be RCD protected.

You need to consider having a separate mini CU serving the shower (MCB + RCD) fed from a Henley block off the main incomer (after the meter, of course ;) ).

But (as mentioned above) and as all good electricians know, we don't wack a 45amp load on an installation without having done some other investigations first about the ability of the supply to support it, and what else is already connected in the house (you know, huge range cooker, sauna in the shed, lathe in the garage, etc etc).
 
Out of interest, is the rcd 63a rating what it can take under normal load or what it can successfully break? Or both the same? For MCB they obviously have different values but for RCD they don't mark the breaking capacity.
I'd have thought they'd need to break more than 63A because if there's a fault to earth that isn't enough to trip the MCB quickly, it would be nice if the rcd could break it first.
 
To be honest, any shower i do these days i strongly recommend a 10mm cable, makes sense for the modest price difference. I think seperate shower consumer will be the way i will go as atleast i can be happy with it.
 
split the tails and install a seperate shower CU with its own RCD and breaker
Best option, customer will be happy as it's cheaper. Just wait by the phone until that old wylex RCCB starts tripping on a weekly basis due to old age! Then you get the CU change as well …….

I give up trying to persuade customers to do something that saves money, as they think your at it !

Regards,

DS
 

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