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Does adding a 16A MCB to a spur meet regs, or do I need a 13A fuse?

Discussion in 'Electrics UK' started by Justin0, 10 Mar 2019.

  1. Justin0

    Justin0

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    Hi,

    I have a new-build with (just about) attached garage which has one double socket and one light socket installed.

    The double socket is connected via a spur from the ring main for the downstairs sockets using a single 2.5mm T&E cable through the wall to the main house. Downstairs sockets are on 32A breaker in CU.

    Likewise the light socket is connected via a spur from the downstairs lighting circuit, through the wall on a single 1mm T&E cable. Downstairs lights are on 6A breaker in CU.

    It's challenging to get any more cable from the main house into the garage.

    I am adding a bunch of extra sockets (using more 2.5mm cable) and lights (using more 1mm cable) in the garage. HOWEVER I am adding the sockets for convenience and I won't be using more than 13A (or maybe 16A) in total at any one time in the garage.

    So I have bought a small garage Consumer Unit with 16A and 6A MCBs (also an RCD which I won't be using, there are two RCDs in the main house CU already). My plan is to add this little CU where the two sets of T&A cable come into the garage. Then, I believe I can safely add as many sockets and lights as I like despite them connecting via spurs.

    I'm pretty happy this is safe. What I don't know is whether it meets regs.

    My understanding regarding the regs is that if I were adding a 13A fuse where the spur comes into the garage, my setup would comply (conceptually all the sockets are then like a fused 13A extension lead).

    Firstly, am I right about that?

    Secondly, can I use the CU I've bought with its 16A MCB instead of the 13A fuse? If not, would a 13A MCB do the job, or would it have to be a fuse for some reason?

    Thirdly, same question for the lights and the 6A MCB. Valid/too high/needs to be a fuse?

    I really appreciate any guidance.

    Oh and when I say "comply" I mean "comply after a qualified electrician has signed off on it", but I'd like to get the installation right myself first.

    Thanks in advance
     
  2. flameport

    flameport

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    13A FCU for the sockets.
    Lights connected directly (they are already on a 6A circuit).
    Consumer unit not required.

    What exactly do you mean by that, and what do you expect to get once this person has done whatever you expect them to do?
     
  3. Justin0

    Justin0

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    Thanks Flameport,

    I take it the 16A MCB is no good then?

    I want to use a breaker rather than a fuse, so that it can be reset easily if tripped. The FCUs I've seen are fuses - can they be breakers too (despite the name)?

    For me, the consumer unit is just a box to hold some MCBs. Is there something more suitable I could buy? Could I use a 13A MCB?

    My understanding is that these days any electrical work should be done or approved by a qualified electrician. I'm thinking for home insurance mainly. I'm not sure what I would ask for, I imagined there would be some bit of paper.
     
  4. AndyPRK

    AndyPRK

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    I would just leave the lights alone, as its a much better setup the way it is.

    Personally I would be fitting a B20 or B25 MCB to the garage sockets which would allow a decent current draw and protect the cable. As to what the regulations think of this, well, they didn't consider this option I guess.

    Ok the B25 maybe pushing things, but at least if you have a 16 or 20 in the garage its easy to reset.

    A 13A fuse would be more difficult to blow, but would probably get hot!
     
  5. JohnW2

    JohnW2

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    Yes, that is correct. If there were a 13A fuse in the feed to all of the sockets (i.e. a 'fused spur') then you could have as many sockets as you wanted.
    If you could find a 13A MCB, then that would be the same as above - so fine. However, you almost certainly won't be able to find a 13A MCB (10A is likely to be 'the next one down').

    I would personally say that feeding the sockets from a 16A MCB (or probably 20A, maybe even 25A) would be fine, and reg-compliant, even though it's not one of the examples given in the regs. 2.5mm² cable is adequately protected by a 16A (or 20A) MCB and, as far as the 'loading at a point on the ring circuit' is concerned, it's not even as high a potential load as one double socket on the ring.
    As has been said, you don't really need a fuse or MCB at all - you could just connect the garage lights to the existing house lights circuit.

    Pragmatically, since you have bought the garage CU, I suppose that you might as well use it as you propose. It's totally redundant as far as the lights are concerned, but does no harm. Using the CU gives you the small advantage of a potential 16A (or 20A) total to sockets in the garage, as compared with 13A if you used a 13A fuse in an FCU.

    Some people will probably argue that using a CU turns the exercise into work which has to be notified (at great cost) to your local authority. Whilst that may be strictly true, I have to say that, as you've said yourself, you intend to use the CU as little more than a junction box.

    Kind Regards, John
     
  6. AndyPRK

    AndyPRK

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    The lights are best left connect to the house lights circuit.

    Should an RCD or MCB trip that supply garage sockets, the garage lights should remain on. A good safety feature.
    There is no point in touching the garage light circuit
     
  7. JohnW2

    JohnW2

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    I don't disagree with that. As I said, there's no reason not to have all garage lights run from the existing (house) lights circuit.

    Kind Regards, John
     
  8. securespark

    securespark

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  9. JohnW2

    JohnW2

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  10. securespark

    securespark

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    I'm sure Moeller still make them. And ABB too, IIRC.
     
  11. JohnW2

    JohnW2

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    Fair enough. I wonder when they would be used?

    In the OP's case, it's obviously moot - because a 16A or 20A (or maybe even 25A) would probably serve his purpose.

    Kind Regards, John
     
  12. Justin0

    Justin0

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    Great point that the spur load for a double socket could actually be 26A anyway, so in fact 20A would be well within this.

    I think what I'd like to do then is get a 20A MCB for the sockets, and a 3A for the lights (connected to the house lighting spur which is 6A in the main house CU). The 3A lighting one should ensure that if there is a fault in the garage lighting, it will trip without the house lights going.

    The notification thing is a bit worrying.

    Is there something that would do the same job (20A and 3A breakers) but would clearly not need notification?

    Thanks for these links - it's good to know if it becomes necessary to replace the MCB with a 13A there is a way.

    It's a good question... what would an electrician give me that could prove my setup was compliant?
     
  13. JohnW2

    JohnW2

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    That's probably what I would do.
    As has been said, the most sensible approach is to simply run the garage lights off the house (6A) lighting circuit, without any additional fuse/MCB. I imagiune that's the present situation - so I'd just keep it at that (extending the present setup if I wanted more lights)
    That 's wishful thinking. In the (very rare) event of a fault in the garage lighting, it's very possible that the 6A MCB would trip before a 3A fuse (or MCB) blew.
    There might be a misunderstanding there, since you wrote ...
    If it is your intention to employ an electrician to do this work, , then, if you employed a 'registered' ('self-certifying') one, then notification is essentially a non-issue. Whilst is could cost you "a few hundred pounds" to notify yourself, it costs almost nothing if a 'registered' electrician does it.
    Little about the regulations is totally "clear" :) Let us know whether you intend to get an electrician to do this work and, if not, we can discuss this aspect further!

    Kind Regards, John
     
  14. Justin0

    Justin0

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    Ah well okay, that's a fair point. I suppose in which case I may be using the MCB solely as a switch for the whole garage lighting circuit.

    Sorry for not being clear enough. My intention is to do the work myself, then a little later get an electrician to inspect it and either say its okay, or do what work is required to make it compliant. This is partly in order to keep costs low (by saving them time doing the grunt work).

    I assumed that if the electrician had inspected the work thoroughly it would be as if they had done it themselves. But to be honest I'm still not entirely clear on when/if a qualified electrician is required, particularly from a home insurance perspective.
     
  15. JohnW2

    JohnW2

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    If you want "a switch for the whole garage lighting circuit" (which isn't a bad idea, so that you could isolate the garage part if it developed a fault), then I would advise you to use just a switch - and would advise a double pole one, to provide total isolation if/when necessary.
    I can't answer for your insurance company. You would have to ask them whether they would accept an 'after-the-event' inspection by an electrician.

    Legally, the only requirements are (a) that whoever does the work (even if DIY) is competent to do it safely and (b) that, if the work is 'notifiable', it is notified (which, as I've said, can cost £000). If you are in England (not Wales), then very little is now notifiable - only (1) "replacing a CU", (2) "installing a new circuit" and (3) work in certain zones of a bathroom. As you can see, in terms of the actual wording of the law, even installing a new CU (rather than 'replacing' one) is strictly not notifiable (presumably a mistake on the part of whoever wrote the law) - but the catch then is that some would argue that anything downstream of a new CU is 'a new circuit' (hence notifiable)!

    In common sense terms, you will just be 'extending' existing circuits which (in England) would not be notifiable. However, silly though it might be, when you start involving a mini-CU and MCBs, some people would probably start wondering about that in terms of the first two of those three 'notifiability' criterion.

    I know what I would do (and I'm not an electrician), but, ultimately, it is for you to decide. Your concerns about insurance may be valid but as far as the law is concerned, if it's any consolation, no-one here is aware of any instance in which anyone has ever been prosecuted for failing to notify notifiable electrical work, per se.

    Kind Regards, John
     
    Last edited: 11 Mar 2019
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