Replacing 9.5kw shower with 9kw

Postby reefflex » Fri Apr 18, 2008 9:48 pm

Hi all,

I have a 9.5kw triton opal shower which was installed professionally in 2001 but has stopped working. Id like to replace it with a Mira Sport 9kw shower and Im wondering what, if anything, do I need to change with the wiring?

The main board is new. The shower is connected to a 32A MCB and a 30mA RCD. The cable is 10mm2 and travels about 3m through hollow walls. It passes through a pull cord switch outside the bathroom, which i guess is a double pole switch for the 9.5kw rated shower.

My questions are:

What, if anything, do I need to change in the wiring? In particular, does the MCB need to be changed to a different A rating?

If i need to change the MCB do I have to isolate the mains at the meter, or just the main switch?

Can I do this work and replace the shower myself? Do I need to get it inspected afterwards?

What kind of earthing?straps should there be on the shower piping?

Thanks for any advice
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Simply Build It

Postby kuzz » Fri Apr 18, 2008 11:09 pm

electrically very easy job. power off. dis con live neutral earth. connect live neutral earth in new shower covers back on power on. that's it.
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Postby chris_on_tour2002 » Sat Apr 19, 2008 9:18 am

you don't have to change the wiring, what you have will do fine. just check that the mcb is big enough, some electric showers call for 45 amp - though if you are going down from a 9.5 to a 9kw it should be fine.

check that the piping has earth bonding, should have already, it may be under the bath (assume its an over the bath shower).

not sure if you have to get it inspected, you are not altering wiring, just changing pretty much like for like although stringent rules apply in bathrooms and kitchens. i'm sure someone on this site will be able to tell you.
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Postby reefflex » Fri Apr 25, 2008 8:33 am

Thanks all or the advice.

Went ahead and did it yesterday and has worked out fine. So far shower runs perfectly without the cable, mcb or d pole swith getting hot after 1 hour so looking good. Hardest thing was actually the plumbing as had to move the access pipe across a bit!
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Postby ericmark » Fri Apr 25, 2008 10:33 am

You may have a problem with MCB as Amps = Watts/Volts but these are rated volts so if your shower is rated 9.5Kw at 240 volts at 230 volts it is only 9.1Kw and 39.6 amp not 41.3 amp of 9.5Kw at 230 volt. As you can see they are all over 32 amp but it does take time to trip and your shower may be not be long enough to trip it. 10mm² will take between 32 and 47 amp when in a wall depending on the insulation in the wall or ceiling. From what you say 40 amp should be OK but only if not an insulated wall.
According to the regulations you should isolate elsewhere and if the supply authority have provided a switch then switch off at there switch. If the consumer unit has been fitted correctly there should be shrouds over the incoming cables so when switched off at the consumer unit no live line connections should be exposed but this is not always the case. Electricians often change items in live boards but if it goes wrong they can end up in court with huge fines on top of the medical problems it may have caused. We read about cases and think "there by the grace of god goes I". As a result I would also be crazy to advise anyone to work on a live board unless I also want to end up in court so really a daft question to ask as no one will ever tell you to live work even if it is safe.

Postby chris_on_tour2002 » Sun Apr 27, 2008 8:57 pm

ericmark - not entirely sure that i follow... are you suggesting that the main switch on the consumer unit may not actually kill the entire house and that there may potentially still be live wires and circuits?

i don't have a switch at the meter. normally to isolate i flick the switch on the ELCB in the belief that it shuts the power off to the entire house, dead as a doornail. might this not be the case?
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Postby ericmark » Sun Apr 27, 2008 11:25 pm

I am not making the rules. Before you work on a board it should be isolated else where not at the board your going to work on so you should pull the fuse once the load is removed or switch off at the switch provided by the supply company. I know many of us don't follow the rules and being electricity at work act I suppose if your not electrician being paid to do the work it does not cover you anyway.

As to an ELCB shutting off power to entire house under the old system RCD's used on TT systems would normally do that and would normally be of the 100 ms S type but the 30ma RCD very rarely switched off complete house. Under the new regulations they would not switch off the whole house.

The Isolator will normally switch off the whole house but not in all cases the use of extra boards using a junction block is quite common where showers etc have been added and the original board could not accommodate either the extra way or the RCD.

I do remember going to a house where the new owners had not moved in to move a socket down the wall to a normal socket height as it was about 5 foot mark all houses in street were built on a slope. Since nothing in the house I just switched off on main switch lights went off so I assumed all dead. By luck I was using a neon screwdriver which lit when I came to remove socket. It was tapped into next doors supply. Never assume always check.

And yes I have worked on many a live board but I would never ask anyone else to work on a live board. Especially one I have never seen and by a DIY person it could be in a very restrictive location and it could have shields missing.

It is very easy to give wrong information when you don't know the job and have no control. Due to finding the earth loop impedance was not good enough I changed a MCB from type D to type B and documented reasons why and raised all the inspection and test paper work. One electrician on contract due to high work load phoned his boss for advice when he found it tripping who in turn advised fitting a type D which when found next morning resulted in that poor guy losing his job. Even though he had done as his boss said but he should have gone to the PC and brought up last test results which he had been shown how to do and he also should have tested which would have shown the earth leakage problem and the change should have been logged rather than it being found by accident that it had been changed back so although far dues to his boss the boss admitted it was him who told him the lad still lost his job. As a result I try to be careful what I tell others to do.

Postby chris_on_tour2002 » Mon Apr 28, 2008 12:27 pm

thanks for the clarification - i just found it interesting to learn that there may not necessarily be one central isolation point.

i should point out that i am not an electrician myself although i do carry out some electrical work in my own home but ONLY if:

a) the work is not restricted under part p (eg adding a socket/fused spur or a light) that will require certification and local authority notification or approval*
b) the power is off and the supply isolated and safe to work on**
c) i have the right tools and equipment for the job and any components such as junction boxes and outlets are the right components to use, have the correct rating and will be correctly located
d) i am absolutely sure that i know exactly what i am doing
e) i am fully aware of my limitations and the extent of my knowledge

*if i am not sure then i find out.
**i have a test meter and know how to use it and i always test to ensure the circuit is dead before i proceed.

[quote]"It is very easy to give wrong information when you don't know the job and have no control......As a result I try to be careful what I tell others to do."

absolutely right - who would disagree? my advice to anybody who is about to take on any diy electrical would be to work through my checklist above and any doubts whatsoever then get in a knowledgable pro. ericmark - don't happen to live in the croydon area do you? :D[/quote]
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