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Discuss fused spur of a fused spur from ring main in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. n180
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    n180 Regular EF Member

    Hi guys,

    whats the regs regarding fused spurs?

    Is it ok to have, from the ring main, a fcu, feeding another fcu, feeding another fcu etc or is it only one fcu per socket like a normal spur?

    I've got a fcu spur from the ring main for a fan in the bathroom. I need to fit in an electric radiator in the bathroom. I'm thinking of taking the feed for the radiator from the FCU spur of the fan. Will that be ok?

    Thanks in advance.
     
  2. Pete999
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    Pete999 Forum Mentor

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    Mate, have a look at APPENDIX 15 in your copy of BS7671, it give you pictorial and written explanation, quite simple to understand and the diagrams are self explanatory. But to answer some of your questions, a spur utilising a FCU is usually used when you need to supply, something that is or has low current requirement, the FCU is designed so that you can fuse down, although it does come with a 13Amp fuse already supplied.
     
  3. n180
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    n180 Regular EF Member

    Thanks pete. I don't have the big one yet as I'm still in college. But I looked at the on site guide and found a note in appendix H, page 183. It basically says the total number of fused spurs is unlimited.

    So I take it, it's absolutley fine to have a fcu fed off a fcu fed of a fcu etc. the Radiator is only 250w so combined with the fan they wont even be pulling 2 amps, so it should all be fine, right?
     
  4. Pete999
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    Pete999 Forum Mentor

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    No a fused spur is what it is what that means is, you can with a fused spur from the RFC as many times as you like, NOT from spur to spur.
     
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  5. Dave OCD
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    Dave OCD Forum Mentor

    Location:
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    Hendry Electrical Services
    Put a 13amp unswitched spur adjacent to the socket, then you can run whatever you like within reason from the outgoing or load side of that.
     
  6. n180
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    n180 Regular EF Member

    Oh right. I totally misunderstood the onsite guide. So basically a spur of a spur is never permitted, even if its fused.

    I'll have to just stick in a juntion box in the ring cables under floorboard and get a fused spur off that.


    Correct me if i'm wrong dave, but what I think your saying here is, I can just stick in the cables for the fan and radiator in the same fcu as they are both low wattage? Is that right?
     
  7. Dave OCD
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    Dave OCD Forum Mentor

    Location:
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    Not really mate as both items should have their own means of isolation with appropriate fuse too. But from the initial FCU you can loop from the SFCU for the heater to another for the fan. If your initial spur from the ring is from under the floor make sure you use a MF connection box rated to at least 32a.
     
  8. rich.250
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    rich.250 Electrician's Arms

    Location:
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    Rich Williams Electrical
    Why 32A??
    Any leg of a RFC only needs to be able to carry 20A.
    So junction boxes can be rated the same.



    Sent from my iPhone using Tapatalk
     
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  9. Dave OCD
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    Dave OCD Forum Mentor

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    I just like to over engineer things when costs are insignificant Rich. :smiley2:
     
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  10. telectrix
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    telectrix Scouser and Proud of It Respected Member

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    think we're going to have to re-christen you Isambard .
     
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  11. rich.250
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    rich.250 Electrician's Arms

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    To be fair Dave,
    The J804 20 amp costs more lol


    Sent from my iPhone using Tapatalk
     
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  12. Flanders
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    Flanders Regular EF Member

    Location:
    Tamworth
    Just a thought but i know the regs says you cant feed more than one point from a ring but what is the difference between two 13 amp fcu and 1 twin socket especially if you are only putting small loads on them and fitting 3 amp fuses
     
  13. Dave OCD
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    Dave OCD Forum Mentor

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    But if you put a 13a unswitched spur straight from the ring you can run 'unlimited' beyond that.
     
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  14. Flanders
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    Flanders Regular EF Member

    Location:
    Tamworth
    Yes i agree with you dave and that would be the way i would do it. It was just a an idea where the regs says you can't run two fsu from one point of a ring (total load 26 amps) but you can fit one twin socket (total load 26 amps)
     
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  15. Lucien Nunes
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    Lucien Nunes Mercury Arc Rectifier Respected Member

    Location:
    London
    You need to be clear how you describe this. If you mean loop in and out of the supply side of a string of FCUs, each supplying one load, then you are constructing a radial branched off a ring which is not permitted. I would tend to accept it where the loads are fixed and small and the FCUs all together, however it would be better to make them part of the ring.

    The other scenario that I don't think you mean, but your description isn't clear, is whether it is acceptable to make a fused spur from a ring and feed the supply side of another FCU from the load side of the first, and so on. This is Dave's suggestion, which doesn't fall foul of the circuit layout as each FCU creates a 'new' circuit with its own characteristics. With 13A fuse in the first one and 3A in the second to fuse a light or fan down from the 13A fused spur, I would think it quite suitable, but you can't really cascade any further as the fuses can't be coordinated.
     
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