Quick question, instead of replacing like-for-like, I'd like to upgrade a 7.5kW shower to 9.5kW, obviously got to change the cable from 6mm to
10mm so this then becomes a "new" install. Is RCD/RCBO protection now mandatory?Lee
Depending on the length, and how the cable is routed, there are circumstances where the 6mm^2 cable will still be adequate. It will depend on the details, but the current carrying capacity of 6mm^2 can be as much as 47A (and your load is 41A)
Not because its a shower as such[1], although fitting one for a shower is very common. However if the cable run is "unprotected" (i.e. cables not enclosed in an earthed metal screen, and its buried in a wall at a depth of less than 50mm), then it would need an RCD to comply with the requirements for cable protection.
[1] Although main and supplementary equipotential bonding will need to be present and to an adequate standard, and you will need to verify the circuit design by calculation.The run of 6mm is roughly 10m, just seems a bit too near its limit for me, iyswim.
Main reason for asking was that it's currently protected by a fuse rather than MCB and I was a little concerned by the possible disconnect time in case of a fault. Have to check the cable route before going further. If a wanted to add an RCBO in an enclosure, is there a way it is permissible to do it from the existing fuseway in the CU or does it
*have* to be done as an additional CU with Henley blocks? If the latter, I think I'd prefer to get someone else to do it and sign it off.Lee
Ok, so having read through the links I can fit an enclosed RCBO via an existing fuseway and on balance this seems an eminently sensible thing to do. Now, assuming the routing of the cable is ok and the thermal rating is not exceeded, does using an RCBO mean that 6mm cable would have a sufficient disconnect time? I still think I'd be happier uprating the cable to 10mm though :)
Lee
If hanging off an existing fuse, then there is no need for a RCBO (i.e. combined RCD and fuse in effect), and an additional RCD would be enough.
An RCD will limit the disconnect time in the event of an earth fault. However is preferable to design where you can such that it would comply even without it. You sometimes also need to consider the disconnect time in the case of a L to N fault, but generally, if its ok on L to E faults then it will be ok on that as well.
If you can furnish some details, we can work through the checks and see...
To start with we need to know:
Details of how the cable is routed - i.e. in a chase plastered into a wall etc?
The total length of cable.
What type of fuse is there currently - rewireable or cartridge fuse?
And if you know it, your earth loop impedance (if your metre has been changed in the last few years this may be written onto a label near or on it - it would say something like "ELI: 0.3 ohms"). If you don't know that, then what type of earthing[1] arrangement have you got? (so we can assume the nominal worst case values).
[1] You can use the details and pictures here to work out which:
I believe that is wrong now.
If you replace the cable with a larger one then the work you have done has to comply with the current regulations which require an rcd for every circuit in a room with a bath or shower.
It is regulation 701.411.3.3
Sorry typo, meant RCD ;)
Thanks, I'll report back when I've had a proper look.
Lee
Even if it to replace a (cough) damaged (/cough) cable?
Regs 510.2 and 134.1.1 apply and I have never seen a shower installation manual that does not require the use of an RCD for the shower.
I disagree. An electric shower could be fitted to a 16th edition regs bathroom if the new shower is integrated with the existing supplementary bonding.
Can you say why you think that and give an authority. All new work has to comply with *current* regulations. I cannot see how this long after the introduction of the 17th edition you can elect to use the 16th (or
15th, 14th, 13th etc) edition.However I would agree with you if you were just changing the shower unit, but not if you are doing any work on the circuit.
Yes, sorry I was not clear. The cable protection issue would only apply if also changing the cable or installing a new circuit. If just changing the shower, on the same cable (assuming the circuit as a whole is adequate) then you would not necessarily need to add the RCD for that reason. Note however that many shower manufacturers instructions will mandate the use of a RCD anyway.
I would have to agree with that - my interpretation would be that an uprated cable/circuit would consitute a new circuit - meaning the current regs apply.
In any case, RCD protection for bathroom circuits is an eminently sensible idea - and there are ways to do this even if the CU cannot conveniently take an RCBO for that "way" - eg add a 30mA RCD in a little box after the CU at a convenient location.
I have not followed the whole thread - but is the OP uprating the protective device (fuse/MCB) to a higher current? If so, that is no longer replacing like with like.
the shower, then its not a new circuit, only a new appliance, and thus doesn't need 'up'grading to the 17th edition requirements.
NT
Regardless of the legal issue you would be very stupid not to have the appropriate protection.
Peter Crosland
But Bruce is a knowledgeable and intelligent bloke. I prefer not to fight with them but debate. It's bellends like dennis that I abuse.
I'm ringing the RSPCD...
;->
Just to update, I was obviously having brain fade because I totally failed to notice the RCD that was already sitting there.
Since the existing 6mm was clipped to surface for it's entire 10m length (runs up the dividing wall then straight in behind the shower unit) and was already protected by a 40A fuse and 45A DP switch I just thought it was easier put a 8.5Kw unit in as a "like for like" replacement.
Lee
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