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Lights Supplied by 30 Amp Ring Final. B.S. 3036 Fuse.

Zoomup
HellOOOoooo All,


I came across a strange one today. I went to change a faulty touch dimmer switch for an ordinary light switch. I discovered that the two lights controlled by the switch did not originate at the lighting circuit, but from a 30 Amp wire fused ring final. The supply was connected to an old metal double socket box below the light switch, in an added conservatory, with a blank plate over it. I can not add a fused connection unit as the box is a double socket box. The blank plate is covered by a small easily removed panel convector heater. I was considering installing an inline fuse holder in the double socket box for the lighting circuit. The lamps are low energy types so overloading is very unlikely, but faults may occur.


Thoughts please.


Z.
  • 0
    Zoomup:

    It is not always possible to easily fuse down before a bathroom or shower room light. I thought that your previous question was about to trick me. 521.8.2 does not apply, as I am only dealing with ONE final circuit, that of the lighting circuit feeding a single timer extractor fan.  No probs. here.




    I think the argument here is that by having separate fuses on the L and SL you have effectively created two final circuits but with a single device connected to both circuits. Which creates all sorts of potential problems. For example even with a fuse removed, the load side of the fuse holder may still be live.


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    Gentlemen, this is not a "borrowed" neutral by any reasonable consideration. Even if you have installed with two fuses, presumably both phase wires and the neutral to the fan are in the same cable? This is not two final circuits, it is only one feeding one appliance. This is a case where correct installation should be followed, one cable to the fan, the phase and switched phase from the switch along with the corresponding circuit neutral (or all together from the light if you want to follow that path of looping in). I really don't see why you want two fuses either, one feeding both fan and light is the obvious route. I really don't understand why the instructions want a fan isolator either, but then they are obviously written by the well-known uninformed author who plagues all the "manufacturers instructions" written to the 16th edition. 521.8.2 does not apply, because the ring is NOT a submain to another DB however many fuses you try to fit.
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    wallywombat:
    Zoomup:

    It is not always possible to easily fuse down before a bathroom or shower room light. I thought that your previous question was about to trick me. 521.8.2 does not apply, as I am only dealing with ONE final circuit, that of the lighting circuit feeding a single timer extractor fan.  No probs. here.




    I think the argument here is that by having separate fuses on the L and SL you have effectively created two final circuits but with a single device connected to both circuits. Which creates all sorts of potential problems. For example even with a fuse removed, the load side of the fuse holder may still be live.




    The fuse holders are all insulated grid type in a suitable insulated enclosure. There is no shock risk as the terminals are recessed.


    Z. 


  • 0
    Zoomup:
    No; F.C.U. with flex outlet that you suggest would not be acceptable to the wife of the house. The single light switch is much neater.



    Z.



    The FCU would be behind the touch controller, The householder would only see the touch controller sticking out a bit by the thickness of the standoff frame.


  • 0
    This fan seems to have an internal fuse mounted on the P.C.B. But not all fans have this fuse.

    https://www.bing.com/videos/search?q=bathroom+fan+isolating+switch&docid=607990116548936697&mid=B859988EEB65CCEAB17CB859988EEB65CCEAB17C&view=detail&FORM=VIRE


    Z.
  • 0
    Zoomup:
    The manufacturers do not supply such a label so obviously consider it unnecessary.


    Z.



    They obviously think that using only one fuse in the way described in the above posts is the correct way to go. There is sometimes a diagram showing this. I have never seen two fuses used for fans. there would be danger if ether fuse blew blew and a lable IMO would be needed, if not within the fan, then on it.


  • 0
    I would certainly not be very comfortable fitting two distinct fuses/breakers to a domestic fan supply. A "fusing down" before the isolator/fan switch split to say the light before the wiring visits the fan would be my way. I would (wrongly) not be over-concerned about not having a 3A fuse to the fan on a 6A B type MCB lighting circuit although it does contravene some manufacturers instructions.


    On a domestic type circuit, although the incompetant should leave well alone, we all know that often they do not.

    In a , hopefully well controlled, commercial setting we might not be as concerned. Although that lack of concern might be a bit misguided .
  • 0
    ebee:

    I would certainly not be very comfortable fitting two distinct fuses/breakers to a domestic fan supply. A "fusing down" before the isolator/fan switch split to say the light before the wiring visits the fan would be my way. I would (wrongly) not be over-concerned about not having a 3A fuse to the fan on a 6A B type MCB lighting circuit although it does contravene some manufacturers instructions.


    On a domestic type circuit, although the incompetant should leave well alone, we all know that often they do not.

    In a , hopefully well controlled, commercial setting we might not be as concerned. Although that lack of concern might be a bit misguided .


    There is no risk as the fan can be completely isolated via the 3 pole fan isolating switch which is made for this purpose. We have three separate fuses in 3 phase supplies to machines and they create no safety problems.


    Z.


  • 0
     There is sometimes a diagram showing this. I have never seen two fuses used for fans. there would be danger if ether fuse blew blew and a lable IMO would be needed, if not within the fan, then on it.


    What danger exactly please?


    Z.


  • 0
    Z, what possible danger can there be requiring a fan isolator switch? You seem to be suggesting that you need to isolate a class 2 fan, which requires tools to dismantle, in case someone starts to fiddle with the wiring? The use of isolators for machinery is because they need maintenance and have exposed moving parts. Fans have finger guards which prevent access to moving parts. Even the most stupid DIYer is not going to disconnect this fan without some reasonable consideration of the power. The danger is of your manufacture because a person might think that they have removed the only fuse when there are actually two to isolate the appliance. Please just fit a single FSU for the light and fan. Job done safely.

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