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Correct wiring for 8.5kw Mira Electric Shower.

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  • 18-12-2011 2:41am
    #1
    CorkHarbour
    Registered Users Posts: 26 ✭


    Hello Everyone,

    I have searched through all the older posts on this subject and have just a few questions that you all that you may be able to answer and or confirm.

    This is a new install of a 8.5kw Mira Electric mains feed shower.

    This house is old but was rewired by a Sparks in the last 10 years approx.
    The main consumer unit is a modern two rail box.
    It has a 63a RCD on top rail feeding Lighing circuits ans the cooker and the immersion is also in this top rail.
    The bottom rail has the 63a Main Fuse Switch and the sockets.

    My questions are please:
    1. A shower CANNOT? or SHOULD NOT? be fitted on the same rail as the cooker?

    2. A 40a RCBO would be the best way to fit to the bottom rail.

    3. A 40a RCBO negates the use of a seprate 32a RCD and a 40a MCB on the shower circuit? Right or Wrong?

    4. Why is it ok to fit a 45a double pole isolator into the circuit? Wouldnt this mean the 40a RCBo would trip first and not the isolator?

    5. A spur can be taken from the bathroom lighting ring to wire a electirc timable extractor fan? Correct?

    Any links, diagrams or advice would be greatly appreciated.

    Thanks in advance!


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    #2
    pieface_ie
    Closed Accounts Posts: 301 ✭✭pieface_ie


    1. A shower CANNOT? or SHOULD NOT? be fitted on the same rail as the cooker?
    Do not take take the distribution board layout as you see it. Just because you see the shower and cooker protective device on the same rail/row it by does not mean they are connected in anyway. There is nothing wrong with this.
    A 40a RCBO would be the best way to fit to the bottom rail.
    ???? You will need to supply more information than this. As above there is no real chronological order that the protective devices should be in. You may see different arrangements/layouts depending on the individual electrician.
    3. A 40a RCBO negates the use of a seprate 32a RCD and a 40a MCB on the shower circuit? Right or Wrong?
    Yes, a MCB+RCB combined into one unit = RCBO.
    Why is it ok to fit a 45a double pole isolator into the circuit? Wouldnt this mean the 40a RCBo would trip first and not the isolator?
    An isolator is not a protective device "mcb type" it can be viewed as a switch in simple terms, just on & off. The 45A isolator = the "switch" is rated to safely carry a current of 45A.
    5. A spur can be taken from the bathroom lighting ring to wire a electirc timable extractor fan? Correct?
    I am not up to speed on the latest regulations concerning domestic installations but I cannot see a problem with it.


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    #3
    maxfresh
    Registered Users Posts: 688 ✭✭✭maxfresh


    1 Shower can be on same rail as cooker as rcbo is fed off non rcd protected phase and neutral

    2 yes

    3 A rcbo is rcd and mcb combined so is neater way and takes up less space in db

    4 isolator is not a protective device it is only to kill power for working on shower

    5 yes .but should be wired through a fan isolator


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    #4
    uncle betty
    Registered Users Posts: 129 ✭✭uncle betty


    CorkHarbour wrote: »
    The main consumer unit is a modern two rail box.

    It has a 63a RCD on top rail feeding Lighing circuits ans the cooker and the immersion is also in this top rail.

    The bottom rail has the 63a Main Fuse Switch and the sockets.

    You sure about all this ?

    Because there's no real need to have lighting circuits protected by an RCD, but there's every need to have the sockets protected by it.

    Maybe it's just the way it reads, but if you're not an electrician maybe you should get one in...


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    #5
    CorkHarbour
    Registered Users Posts: 26 ✭CorkHarbour


    First of all, thank you all so much for the really fast replies, you have cleared some of the doubts from the auld noggin.

    You know how it is when you are on your tod and have no one to bounce an idea off.

    Thanks for reminding me about the rails, I was looking at the MCU without it's front panel off.
    And then I was over thinking the isolator as something more than a manual switch for safety.

    If I didnt use an rcbo, the correct sequence would be 63a 30ma RCD and then a 40 amp MCB then a 45a double pole isolator then shower unit. Correct?

    Uncle Betty:
    I do not have access to the MCU until tomorrow but I will double check the unit but I think i am remembering it right.

    The MCU wiring in the attic is a bit of a mess really, It took me half an hour to identify all the different MCBs and what they did, the begger who fitted is didn't even write down the address of each point.

    I was wandering around the house with lamps on and a power too in hand to plug into sockets.

    You are dead right about safety though, I am NOT an electician and will be getting all my work checked and certified by a registered installer but I am doing this job for my elderly uncle and he has been ripped off time and time again, so he is loath to let anyone do work in the house anymore.

    Thank again for your replies.


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    #6
    uncle betty
    Registered Users Posts: 129 ✭✭uncle betty


    CorkHarbour wrote: »
    If I didnt use an rcbo, the correct sequence would be 32ma RCD and then a 40 amp MCB then a 45a double pole isolator then shower unit. Correct?

    Uncle Betty:
    I do not have access to the MCU until tomorrow but I will double check the unit but I thin i am remembering it right.

    No problem, it'll be interesting to see what you find.

    I just wanted to highlight what you put there as 32ma. As far as I know, the sensitivity of an RCD is 30ma.

    You may be referring to the rating of the RCD as 32 Amp - ie the amount of current it can carry.

    The lads who do domestic work will be able to give you a more practical everyday answer than I can, but I wonder if 32 amp will be enough for an 8.5 kw shower ?

    8500 watts / 240 volts = 35.4 amp

    I don't know if you are allowed diversity for a shower supply. I don't think there'd be any problem with having a 40A RCD.

    Maybe wait and see what other posters think ?

    Best of luck.


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    #7
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    CorkHarbour wrote: »
    First of all, thank you all so much for the really fast replies, you have cleared some of the doubts from the auld noggin.

    You know how it is when you are on your tod and have no one to bounce an idea of.

    Thanks for reminding me about the rails, i was looking at the MCU without itys front panel off.
    And the I was over thinking the isolator as something more than a manual switch for safety.

    If I didnt use an rcbo, the correct sequence would be 32ma RCD and then a 40 amp MCB then a 45a double pole isolator then shower unit. Correct?

    Uncle Betty:
    I do not have access to the MCU until tomorrow but I will double check the unit but I thin i am remembering it right.

    The MCU wiring in the attic is a bit of a mess really, It took me half an hour to identify all the different MCBs and what they did, the begger who fitted is didnt even write down the address of each point.

    I was wandering around the house with lamps on and a power too in hand to plug into sockets.

    You are dead right about safety though, I am NOT an electician and will be getting all my work checked and certified by a registered installer but I am doing this job for my elderly uncle and he has been ripped off time and time again, so he is loath to let anyone do work in the house anymore.

    Thank again for your replies.

    you should hire an electrician if you're concerned about your uncle


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    #8
    maxfresh
    Registered Users Posts: 688 ✭✭✭maxfresh


    If your going to use a separate rcd and mcb ,the rcd would be rated for 63 amps with a tripping current of 30 ma

    and a mcb of 40 amps

    easier to get a 40 amp rcbo

    make sure all connection are good and tight


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    #9
    CorkHarbour
    Registered Users Posts: 26 ✭CorkHarbour


    Hello All,

    I've edited my mistake in spelling on the above post.

    I meant a 63a 30ma RCD and then a 40 amp MCB.

    I have gotten a RCBO that is up to the task.
    you should hire an electrician if you're concerned about your uncle

    I have an a registered quailified electrician doing me a favor and coming to check the work fully, I want to help my uncle and I want to find out how to do the work but I dont want to kill him.
    Dont worry I am a tradesmen myself, so I know my limits and try not to exceed them.

    Thanks for all your help guys, I'll post afterwards to let you know how I got on.


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    #10
    liveandnetural
    Registered Users Posts: 270 ✭✭liveandnetural


    http://www.examiner.ie/ireland/tributes-for-gaa-player-electrocuted-in-shower-177085.html


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    #11
    CorkHarbour
    Registered Users Posts: 26 ✭CorkHarbour


    Hello All,

    Uncle Betty:
    Your right, my memory was faulty, the RCD was protecting the sockets.
    liveandnetural wrote: »
    http://www.examiner.ie/ireland/tributes-for-gaa-player-electrocuted-in-shower-177085.html

    Thank you Liveandnetural! The poor guy, I wont even power on the shower until an electrician checks it.


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    #12
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    I wouldnt like to be checking it after you


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    #13
    .G.
    Registered Users Posts: 5,415 ✭✭✭.G.


    Agree with M cebee.

    OP,not being funny but judging by your descriptions and observations in this thread your electrical knowledge is flaky at best and most likely to get you into some bother while undertaking this job.If you really want to help your uncle you should hire a registered electrical contractor and let them do the work.


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    #14
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    I wouldnt like to be checking it after you

    just jump in and try it, or hobble in in my case:D


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    #15
    cast_iron
    Registered Users Posts: 2,454 ✭✭✭cast_iron


    robbie7730 wrote: »
    just jump in and try it, or hobble in in my case:D
    Bit of a shock might just the tonic for that leg. :)


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    #16
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    cast_iron wrote: »
    Bit of a shock might just the tonic for that leg. :)

    I know, had a look at one of xrays yesterday, im changing my story to a parachute failing to open:D.


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    #17
    uncle betty
    Registered Users Posts: 129 ✭✭uncle betty


    M cebee wrote: »
    I wouldnt like to be checking it after you

    Fair play to you for knowing your limitations.


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    #18
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    You will be doing well to find many limitations there in my opinion.


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    #19
    uncle betty
    Registered Users Posts: 129 ✭✭uncle betty


    robbie7730 wrote: »
    You will be doing well to find many limitations there in my opinion.

    I was being sarcastic. In response to a pointlessly smartass post.


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    #20
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    uncle betty wrote: »
    I was being sarcastic.

    I realise that, i just think the general message in the thread is to get it done properly. They are a simple install in electrical terms, for a competent electrician. As indeed is the plumbing aspect of it for anyone experienced in that.

    But for the non electrician, sound proper connections are not all that simple, particularly at the DB. If it works, that wont mean its properly installed to a good standard.


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    #21
    CorkHarbour
    Registered Users Posts: 26 ✭CorkHarbour


    Just wanted to say thanks you to everyone for ALL your comments, bath room retiled and shower installed and checked by quailified competent sparks, I even bonded the pipes in the bathroom which the amazed me didnt have a strap anywhere.

    Happy Christmas to you all.

    Cheers CorkHarbour


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    #22
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    Not to be recommended the giant leap you have taken from asking basic questions to wiring a shower and bathroom bonding

    Everybodys happy til someone gets electrocuted with bathroom diy


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    #23
    CorkHarbour
    Registered Users Posts: 26 ✭CorkHarbour


    That's very true mcb, but I am not novice diyer, i'm a tradesman of 15 years in the marine and maritime industry, I hold a engineering officer of the watch ticket meaning on alot of coastal vessels I am the electrician, how scary is that. I do the very basic sparky stuff like change fuses, wire motors and pumps every other week, i'm well used to earthing requirements and electrical safety onboard vessels. Which is why I was confirming a questions that i had in head at the time because i'm not used to domestic arrangements, there its no such thing a stupid question, i think you will agree. If you don't know or are not sure, ask ! But I will whole heartedly agree the average diyer shouldn't do what I just did. Oh and I genuinely thank you for your concern and level headed advice, alot of people would have just bigged themselves up or gone on a rant. Have a good christmas kid!


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