Shower circuit options.

[fannybaws]

Hello All,

Done a search and have had a read of other posts but cant find any help with my questions. It is quite specific though

I plan on installing a power shower. It is the gravity fed type that doesn't heat the water so relatively low power. Thinking of a TRITON AS2000, I would like advise on the best way to wire it under these circumstances:

I am in a top floor flat with access to the attic above. There is an old shower circuit (radial) 6mm2 in place from an old shower now removed.

I am going to use this existing cable from the CU to the attic (Dont fancy running a new one as the cable run to the CU is a nightmare - between 2 bay windows). 6mm2 is obviously overkill (recommended 1mm2 off a ring main) but it is there and will be getting used ! I am wondering if I could use this cable to stick a light up in the attic as well. To add to the confusion I need to fit a 30mA RCD in line as the old CU downstairs wont take one!

What is the best way to do this ? I have thought of the following options:

1) Terminate the 6mm2 in the attic into a junction box, from here, wire a light (via a switch) and the shower (via an inline 30mA RCD and a 3A fused pull switch) in parallel. (appropriate MCB in CU.)

2) Terminate the 6mm2 into a 2 way RCD protected mini CU, from here wire the light and the shower The 2 way CU will have appropriately rated MCB's as will the main CU downstairs.

3) Forget the light, step the 6mm2 down to 2.5mm2 in the attic via a junction box (Doubt the terminals on the shower will take 6mm2).

I realise the 2 options involving the light have drawbacks. I guess a shower circuit should have its own circuit and I imagine a second 2 way CU upstairs should be wired from the source as opposed to a slot in the first CU.

Is any of these options do-able ? Or are there any better solutions that don't involve running a new cable to the CU ?

Any help greatly appreciated

Sorry for the length of post!

 

[andy]

add a mini CU next to the main CU with an RCD. at the other end have another mini CU but with 2 breakers. 6A for the light and 6A for the shower

 

[brown-nought]

What route does the cable currently take? Does the 6mm go via the attic? If it does you have a few options. If it does not things are more limited.

Assuming the 6mm runs into the attic:-

Since the power shower doesn’t heat the water it doesn’t need to be on a dedicated circuit. It is however in Zone 1 and will need to be protected by an RCD and bonded into the bathrooms supplemental bonding. (Read other posts on this – there are lots).

I’m guessing the old 6mm cable was to supply an electric shower – in which case there should have been a DP pull switch near the shower/bathroom? Is the 6mm cable protected by a 32A MCB or 30A fuse at the CU? If it is higher it must be reduced to a max of 32A.

If you treated the 6mm supply as a radial circuit you could also supply a light via an FCU.

My suggestion would be to re-run the 6mm in the roof through the ceiling into 2 surface mounted FCU’s located outside the bathroom. The first FCU should be an combined RCD FCU with 30 ma trip. This could be used to supply the power shower via the old DP pull switch. Protect it with a 3A fuse (of as instructed by the shower instructions) and run 1.5mm to the shower (or use the existing 6mm if it reaches).

The second FCU can be used to supply the roof light. This would need another 3 or 5A fuse. To prevent arguments I’d use a short piece of 6mm cable between the FCU’s.

The MCB/Fuse way at the CU would need to be re-labelled as a radial circuit supplying the shower and light. (Strictly speaking you should review the MCB order as normally (correctly) the highest load should be in the first way after the incomer isolator.

Before you buy the shower I’d check that you have sufficient “head” on your water supply.

In 2005 this is under Part P.

 

[fannybaws]

Thanks for the replies gents

I Should have clarified cable routing. I am in a 1st floor flat (nobody above, access to attic/roof space). CU is housed in a small cupboard in a bedroom, existing 6mm2 shower cable goes in a void between 2 bay windows up into the attic, goes to a DP switch, then to the old shower (now gone). Fitting a new cable is a nuisance, had to fit a 10mm2 Radial for a cooker earlier this year and it was very tricky !

Andrew, that is a lot of mini CU but it is an option thanks

brown-nought, Good info there The fact the shower doesn't have to be on a dedicated circuit is a surprise, thanks for the info. Embarrased to admit I don't know what a FCU is (Fused consumer unit ?) Your advice is to fit an RCD (lets call a FCU a mini consumer unit for us doughballs who don't know the terminology! Please correct my ignorance) mini consumer unit for the Shower as described, then another for the light ? Would a fused spur not do the job for the light?

Also, when you mention bonding, you mean the pipes right ? I know about that! Got the 'head' covered as well (75mm requiured to prime the pump)

This is solid gold gents, thanks for your help.

 

[brown-nought]

FCU - Fuse Connection Unit - its a fused DP switch the same size as a single socket - do a search on the site for pictures. An RCD FCU has a RCD integrated into the FCU package.

[code:1]
CU----6mm ------ FCU(RCD/3a) ------- 6mm ----- FCU/5a
| |
| |
DP Pull Switch Light Switch
| |
Shower Pump Light
[/code:1]

 

[fannybaws]

brown-nought,

Thanks for the effort you have went to there
That is exactly the way I shall do it.

You are a scholar and a gentleman

 

[fannybaws]

Hello again, is brown-nought about ?
or some other like minded fellow ?

I eventually got round to this job after the festivities and have encountered a slight problem. In brown noughts example there are 2 6mm cables coming from the fcu/rcd unit. As the load terminals do not take the cross section I joined them in a 30A J/box such:

CU---6mm ---- FCU(RCD/3a) ----6mm-----J/Box- ---6mm --- FCU/5a
................................................................| ............................|
................................................................| ............................|
....................................................DP Pull Switch.............Light Switch
................................................................|.............................|
.....................................................Shower Pump...................Light

Is this OK?

The shower (pump) is not connected at present but the Pull switch is switched off.

After doing this and testing the light would not work !

I did get it to work after pressing one of the buttons on the RCD - 'On' I think

The other button is 'Test' which didn't go Red after pressing although was making a buzzing noise!

The light switch must have been ON as the light came on. Turning off the light switch switched the light off. PROBLEM - Switching the light back on did not work. The RCD unit 'Test' button can not now be pressed in at all! Pressing the 'ON' button does nothing as well

Can anybody think of what I may have done wrong ? I am cluless with these RCD spur units.

Cheers !!

 

[notb665]

Your FCU/3a is before the shower pump and the light. So the FCU/5a is redundant.

I think Brown Nought meant the 6mm goes in and out of the supply terminals in the 1st FCU, or to use a junction box:

--6mm----JB-------6mm
...............|.............|
...............|.............|
.............FCU.........FCU
...............|.............|
..............etc..........etc

 

[fannybaws]

notb665, of course it is redundant. I am a muppet.

What was I thinking
Thanks

 

[mapj1]

However, if you cant turn the RCD on, it usually means it has decided there is a fault. It is possible there really is a fault, but if the parts are new, and dry and correctly wired, it is more likely you have swapped the source and load sides of the RCD part - the RCD actually detects the difference in live current going to the fitting, and neutral coming back - if equal and opposite curents don't cancel, it trips, as this normally means electrons leaving the live, and coming back via earth, or the plumbing or something that is not neutral, which normaly means its time to cut the power off...
However, if you wire the neutrals through the trip in the opposite way to the live, or indead there if is a 'sneak round' path (load side neutral joining up to another circuits neutral, or to the earth is surprisingly common) then this cancellation does not occur properly, the trip will 'trip' as it were and keep doing so until the 'fault' is removed. Best to check the wiring very carefully - are you using the live in-live out, neutral in-neutral out as the makers intended?.
Should be fine as drawn apart from that.
Regards M.