Advice Needed Re Shower Cabling

Discussion in 'Electricians' Talk' started by Capt. Cabbage, Feb 10, 2004.

  1. Capt. Cabbage

    Capt. Cabbage New Member

    Can anyone give me some advice on the following...

    I am in the process of installing an electric shower at home and I have had a couple of conflicting opinions about what earth cabling is needed.

    The shower is a 9.8Kw model and I have run some 10mm T+E to the bathroom already (Mostly surface clipped / under floorboards, with the last metre to be run down the wall underneath the tiles if that makes any difference?)

    While searching the forums so far, I cannot find a definate answer to the following...

    Do I need (Or is it strongly recommended) to run a seperate earth cable back to the fusebox and if so, what size should the cable be?

    So far 1 electrician has informed me that I should run a seperate earth cable back, while another says that the earth in the T+E will be suitable.

    As you can probably tell, I am not an electrician, so plain worded (And simple to understand!) replies would be most appreciated!

    Thanks in advance.
  2. The Trician

    The Trician New Member

    I would suggest that you proceed as you previously planned. Connect the 10.00mm single earth cable to both the shower and the main earth terminal in your consumer unit. Some people just bond to the nearest earth terminal in a bathroom/hallway, but since this is just usually a 1.00mm earth cable in a light fitting or ceiling rose, then the potential earth fault current would be too big for the cable. Others rely upon the earth (cpc) in the 10.00mm twin+earth cable. Basically its all about whether or not the earth fault loop impedence value is low enough to meet the disconnection time in BS7671. By running a seperate 10.00mm earth back you should not experience any problems with this.
  3. Damocles

    Damocles New Member

    Answer to your question should already be on here somewhere.try using search for bathroom and the magic word 'bonding'.

    All exposed earthed metalwork in a bathroom should be connected by earth wires somewhere in or near the bathroom. For example, behind the basin. The important thing is that everything is connected so that there can not be a different voltage between anything, so you can't ever end up holding one thing which is live and another which is earthed. Once this is done, the earths which are already connected with any supply wires should be enough to blow fuses or switch things off if their is a fault.

    You dont have to earth metal which is not connected to anything,like toilet roll holders or towel rails. But you do radiators, because they are earthed by the pipes.

    But they like you to have an RCD so things get switched off double fast, if anything does go wrong.
  4. The Trician

    The Trician New Member

    Yes, forgot to mention the RCD. If you're stuck for room in your consumer unit you'll find that an RCBO might be a better bet, these can be obtained in a '1-way' configuration, i.e. they only take up one 'way' in your CU. Something like a 45A 30ma one should do.
  5. unphased

    unphased Screwfix Select

    Just a couple of points to add. The Regs. require that supplementary bonding is provided in a bathroom. This means that you must not rely solely on the cpc in the 10mm T&E cable alone. The sparky who told you that you could should know better! I always use a 6mm2 earth bond from the terminal in the shower back to the board. It is easier to do this at the same time as pulling in the main 10mm2 T&E. If you havent done this it is acceptable in the regs to use another cpc as supplementary bonding. Take a bond from your shower in to say a nearby earth point in a ceiling rose.

    Second point is the RCD. I would recommend that you use one on the circuit. If not all ready in your fuseboard either a replacemnt fuse with RCBO or on a separate one way CU. You would need a 60A/30mA rated RCD. 40A not quite enough on 9.8kW.

  6. gerrin2owd

    gerrin2owd New Member

    The way I see this is that if you have 10mm T&E cable feeding a shower use the earth (cpc)to connect to the shower earth terminal, then take a 4mm single bonding cable to anything that requires bonding (for explanation follow link)

    No need for "another" bonding cable back to board if the main water and gas services have been bonded correctly and definitely no need to bond to lighting.
  7. Capt. Cabbage

    Capt. Cabbage New Member

    Many thanks for all your answers everyone! Looks like I will be adding a seperate 10mm earth cable back to the CU as I am unsure of the exact state of the bonding in the bathroom currently!

    As per usual, answering one question has led to another...

    As my existing (At a guess, fairly old) CU is currently full (even without making space for the shower) at the moment. I am guessing that maybe it is time for a replacement?

    Taking into acount the fact that all of you recommend the adding of an RCD, would the folowing spec of CU provide everything I need, or would I need anything else, or am I just being a muppet and not understanding?

    12 WAY KIT BOX C/W 10 MCBS (SF Item No 82204)

    Pre-assembled 6+6 split load Consumer unit C/W 10 Type B 6kA SP MCB's. Comprises 100A DP Isolator, 63A 30mA RCD; 1 x 40A, 4 x 32A, 2 x 16A, 3 x 6A, 2 x Blanks. BS EN 60439-3;1991.

    How big a job is it to replace the CU? (For a qualified spark - not me!). Will I be looking at a bill for 1hour of work or 20?

    Thanks again.
  8. unphased

    unphased Screwfix Select

    Hi capt

    Your choice of board would be okay. However, I am reluctant to say go ahead and fit one. Best left to a sparky as unless you know exactly what your doing you could get into a lot of trouble. Takes a good couple of hours to do well!

    Anyway, to help you with the choice of fuses the 16A ones might not be of much use. Use 40A on your shower, use 32A on cooker and socket rings, use 6A on your lighting. If you have an immersion use 16A. If you tell me what circuits you have or desire to have I can be more specific.

  9. unphased

    unphased Screwfix Select

    btw Put the lighting on non RCD side and the rest on the RCD
  10. ban-all-sheds

    ban-all-sheds New Member

    Err - can't make it out in the photo - does that little label in the top LH corner say Volex?

    Put the fridge/freezer on a non-RCD circuit as well.

    40A for a 9.8kW shower? If that's 9.8kW at 230V, then it'll draw 42.6A, and if the supply voltage rises to 240V, 44.5A...

    And finally, let your electrician supply the CU.

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