Question for electricians about shower size and cable capacity

Discussion in 'General Chat' started by Stuart Wright, Jan 2, 2012.

  1. Stuart Wright

    Stuart Wright
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    Hello folks,
    we have a shower which has an Opus 4 electric unit on the wall.
    It went bang the other day (literally) and tripped the dedicated 30 amp circuit breaker for the shower.

    There is no information on the Opus 4 on the 'net so I emailed the manufacturers who mailed back today (impressively promptly) with the specs. 7kw, 1 bar minimum. The shower hasn't been made for several years.
    The cold water supply is from a pipe which is about 10mm in diameter. There is no sign of an electrical cable as it's been tiled in, but there is a separate pull chord in the ceiling with an amber light which, after the circuit breaker was reset, does come back on. The shower also still pumps water out, but doesn't heat it any more.
    The closest source for the electricity supply is a next-door-but one boiler room which has a dark grey rectangular cable, about 9mm x 5mm which disappears into the wall up high in the direction of the shower.

    The water pressure is good.

    So my question is whether a 7.5kw replacement shower (don't seem to be able to get lower than 7.5) would be ok, or whether we could even step up to a higher powered one.
    I would want a decent shower as it's used daily by the family. I do want a thermostatic shower.

    Thanks for any advice you can give.
     
  2. noiseboy72

    noiseboy72
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    Watts is calcualted as volts x amps, so if you know the power in watts, you can work out the current required. 7500W / 230V = 32A.

    The cable to your shower should be a minimum of 6mm (The diameter of the live and neutral conductor.

    From the sounds of it, your current installation will be fine for a 7.5KW shower, but insufficent for a 9.4-10Kw type.

    As this is a bathroom installation, it will need to be carried out or at least signed off by an electrician in any case.
     
  3. Stuart Wright

    Stuart Wright
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    So I'd need to upgrade the trip to higher than 30A to get a bigger than 7kw shower?
    It's a dedicated shower, not a bathroom. Does that make any difference?

    [Edit : The rooms in question are in a separate part of the house. The photo of the fuse box serving those rooms is attached. I can't read the writing above the left 20a fuse. The 15a fuse says plugs (there is just a double socket in the boiler room), the 20a fuse second from right says sauna (it has a 4.5kw heater), and the 30a fuse says shower. That one had tripped. An electrician will recognise the cables and know their rating, I'm sure.]
     

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  4. noiseboy72

    noiseboy72
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    It looks like you will need to upgrade the trip and cable, but an electrician would need to advise as the picture is not totally clear. You might also want to upgrade to a more modern fuse box with built in RCDs.

    But in answer to your question, a direct swap out will limit you to a 7KW shower.

    Any "Wet Room" electrical install needs to be carried out or signed off by an electrician. Failure to do so will invalidate your household insurance and could make your home unsaleable.
     
  5. Berties

    Berties
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    Apparently they can't do any electrical work until the fuse box is changed to meet latest standard.

    That includes the shower socket? And fan extractor? We did those ourselves (dad is an electrician)
     
  6. noiseboy72

    noiseboy72
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    Part P states the following as notifiable and not notifiable. Put simply a qualified electrician must carry out the work.

    Areas within a kitchen, bathroom, garden or special location
    NOTIFIABLE:
    A complete new installation or rewiring
    Installing a new circuit (eg, for socket outlets, lighting or shower)
    Fitting and connecting a shower to an existing point
    Replacing a fuse board
    Adding a socket outlet to an existing circuit
    Adding a lighting point to an existing circuit
    Fitting a storage heater to an existing adjacent point
    Installing a supply to a garden shed, garage or other outbuilding
    Installing a lighting point or socket outlet in a garden shed, garage or other outbuilding
    Installing a garden pond pump including the supply
    Installing electric under floor or ceiling heating
    Installing an electricity generator

    NOT NOTIFIABLE:
    Connecting a cooker to an existing connection unit
    Replacing a damaged cable for a single circuit (cable to be the same size and type and installed as original)
    Replacing a damaged accessory such as a light switch or socket outlet
    Replacing a light fitting
    Connecting an item of equipment to an existing adjacent connection point
    Fitting a storage heater to an existing adjacent point
    Replacing an immersion heater

    Areas not in a kitchen, bathroom, garden or special location
    NOTIFIABLE:
    A complete new installation or rewiring
    Installing a new circuit e.g. for socket outlets, lighting or shower
    Replacing a fuse board
    Installing a lighting point or socket outlet outdoors
    Installing and fitting a storage heater including the circuit
    Installing electric under floor or ceiling heating
    Installing an electricity generator

    NOT NOTIFIABLE:
    Adding a socket outlet to an existing circuit
    Adding a lighting point to an existing circuit
    Connecting a cooker to an existing connection unit
    Replacing a damaged cable for a single circuit (cable to be the same size and type and installed as original)
    Replacing a damaged accessory such as a light switch or socket outlet
    Replacing a light fitting
    Connecting an item of equipment to an existing adjacent connection point
    Fitting a storage heater to an existing adjacent point
    Replacing an immersion heater

    I incorrectly stated above that you can carry out the work and ask an electrician to sign it off. By the book, the electrician must carry out the work. In reality, most electricians will sign off a simple installation if all parts of the work are visible.
     
  7. Stuart Wright

    Stuart Wright
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    Changing the fuse box is not a problem. We have an electrician. However, changing the cable is not an option as it travels too far through non-accessible roof spaces and walls. Is the existing cable not good enough for a 9.5kw shower?
     
  8. nheather

    nheather
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    Are you sure that you have a dedicated circuit for the shower at the moment.

    I can see

    2x 20A - lighting circuits, I guess
    1x 30A - ring main sockets
    1x 45A - what is this for

    Are you sure the 45A is for shower and not for an electric oven outlet?

    Also looking at the picture, I can't see any 45A size cable leaving that consumer unit.

    I guess the question I'm asking is "has the shower been installed on a dedicated high amp circuit or has it been taken off the normal ring mains".

    You can get away with the latter electrically, but it wouldn't pass inspection.

    Cheers,

    Nigel

    Actually, the more I read it the more the fuses look like 15, 20, 20, 30.

    On my consumer unit the two ring main socket circuits are on 32A, the lights are on 6A, the imersion heater on 20A and the cooker on 40A. I don't have an electric heated shower because it was going to be a real pain putting a 50A fuse in and routing the massive cable upto the bathroom.
     
    Last edited: Jan 2, 2012
  9. lynx

    lynx
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    Stuart, your board is a little dated and could benefit from an update...Dual RCD 17th Edition Consumer Units

    Ask your electrician his thoughts on this.

    Is there another board not shown in the image?
     
  10. noiseboy72

    noiseboy72
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    For 9.4KW, you need 10mm diameter cable and a 45A fuse. Your electictrician will be able to tell in an instant if its up to the job.

    6mm cable is simply not up to the job and could / will get hot in use. This is dangerous and will also limit the amount of power getting to the shower. If you cannot pull in a new cable, go for a 7KW shower.
     
  11. niceguy235uk

    niceguy235uk
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    Glad to see voltage drop has been mentioned.

    And 6mm is NOT the diameter of the cable, it is the cross sectional area of the conductors.

    Moving on... The new shower WILL need 30ma RCD protection if it states it in the instruction manual.

    You DO NOT need to touch your existing consumer unit, as a stand alone unit can be installed alongside, however, main earthing and bonding will need to be upgraded if needed.

    You DO NOT need to upgrade anything else in bathroom, if all you are renewing is the shower.

    You CAN just swap out the shower for a new one of similar rating and you DO NOT need to notify, however, as stated above, if it requires an RCD then it will.

    If you install a new shower and supply cable, it WILL need to installed and certified by a registered competent electrician.

    If you have an electrician, why are you asking on here?
     
    Last edited: Jan 2, 2012
  12. Stuart Wright

    Stuart Wright
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    As I mentioned above, it's 20,15,20,30 supplying the electrics in the far section of the house.

    Yes there is the main fusebox which has 16 or so trips in it.

    I wanted to get other opinions and suggestions.
    Most showers for sale are 7.5kw which I guess is in keeping with 32A fuses.
    Thanks for your input.
     
  13. noiseboy72

    noiseboy72
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    I would only disagree on the fitting of the shower. My understanding of the regs is that swapping out of a shower qualifies as fitting a new one to an existing cable.

    And yes, my use of the phrase diameter for the cable was in error. It should of course be cross sectional area.
     
  14. Digital Tench

    Digital Tench
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    Rubbish, the regs do not cover what has been installed previously. The sparky involved would simply have to ensure any new installation was up to regs and that can be achieved by installing a seperate RCD or RCBO circuit and ensuring all bonding requirements are met.

    Edit:- beaten by niceguy
     
  15. niceguy235uk

    niceguy235uk
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    Have a read of Approved Doc P, Page 9, Sec m.
     
  16. IronGiant

    IronGiant
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    Would I be correct that swapping like for like is not notifiable, but fitting a shower to an existing point, where there previously was no shower would? Even if the point was installed with a future shower in mind?

    And in similar vein, upgrading is notifiable? And how flexible is like for like? My shower is getting a bit clogged internally, if I swap it for an identical wattage is that good enough?
     
    Last edited: Jan 3, 2012
  17. niceguy235uk

    niceguy235uk
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    Jesus Dave, you dont half make things complicated.:p

    Allow me..

    Quote..

    "m. The fitting and replacement of cookers and electric showers is not notifiable unless a new circuit is needed."

    Edit:

    And after your edit and in answer to your final question, yes, providing the circuit has RCD protection if the manufacturers specify it.

    Assuming you were happy with the previous shower rating.
     
    Last edited: Jan 3, 2012
  18. IronGiant

    IronGiant
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    Thanks :D
     
  19. Stuart Wright

    Stuart Wright
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    Anyone know whether there is a 7.5kw thermostatic shower? Mira and Triton don't do them. 8.5kw is the minimum power with those brands.
     
  20. lynx

    lynx
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    Last edited: Jan 4, 2012
  21. IronGiant

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  22. its_all_Greek

    its_all_Greek
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    Mira Sport 7.5KW shower a tad expensive but i found it after only a quick search although there doesn't seem to be that many about

    Edit: I see others have beat me to it
     
  23. IronGiant

    IronGiant
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    You get used to that in GC :laugh:

    Which I think is a good thing, just goes to show how many helpful people there are on here :thumbsup:
     
  24. its_all_Greek

    its_all_Greek
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    or people with to much time on their hands:D
     
  25. noiseboy72

    noiseboy72
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  26. niceguy235uk

    niceguy235uk
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    Last edited: Jan 4, 2012
  27. Stuart Wright

    Stuart Wright
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    Thanks everyone. I did the same google search and found the same pages.
    If thermostatic means it keeps a constant temperature despite changing water pressure/temperature, then I don't think the Triton does that.
    On the Mira website, when choosing a model, if you click 'thermostatic', the 7.5kw option becomes unavailable, so I assumed the Mira Sport 7.5kw was not thermostatic. It's also three times the price. I would normally go for a Miele rather than a Hotpoint, but does anyone know whether the higher price is worth it?
    We'll be using the shower between 2 and 8 times a day.
     
  28. IronGiant

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    Aha, it's me again :D my one is a Mira, do you think it's worth me looking for a replacement heater unit on an 8 year old unit?

    Dave
     
  29. IronGiant

    IronGiant
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    What does the Opus 4 do? or did :), otherwise we are in the dark...
     
  30. RottenFox

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    We've got a Sport, my parent's have a Zest(coming up for 2 years old, they haven't changed anything I think), not much in it TBH, they get you wet, you wash, switch off.
    Both never missed a beat.
    Both good showers, not had to try out the Sport's extra features such as Optiflow, or Sensiflow.
     

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