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

Weirdbeard:

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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.

The faulty touch dimmer switch was probably originally a switched fuse spur? Replace faulty dimmer with a switch fuse spur, job done no heaters need removing! :)

 

I think not as it has a 1.0mm2 T&E as a supply in from the socket below and a 1.0mm2 T&E out also travelling downwards on what was an outside wall before the extension/conservatory was built. Probably a builder's bodge.


Z.

 

Also the label reg i was thinking of is 514.11.1 it does say not capable of being isolated by a single device, and you could argue the 6A mcb does this, but then so does the main switch and cut out. I think the intention is that it warns of a possible danger of live parts if one of the fuses blows and the fan dont work. 

 

The notice "shall be fixed in each position where there are live parts which are not capable of being isolated by a single device."


The fan can be isolated by the single lighting M.C.B.


or  the 3 pole fan isolator.


Also there are no live parts accessible to cause danger. Everything is enclosed and/or insulated.


So 514.11.1 does not apply.


It might apply to say a night storage heater with a normal on peak heater build in as well as the off peak,  where there are two distinct supplies with two different supply switches.


Z.

Zoomup:

Treat bathroom fans with respect, they can and do catch fire.

Extractor fan causes fire in Chester (cheshirefire.gov.uk)

Faulty extractor fan fire in Limehouse | London Fire Brigade (london-fire.gov.uk)


Z.

Further reading on extractor fans and fusing :

https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=44616

mapj1:

The traditional inside out squirrel cage induction motor ones actually draw less current when stalled than when spinning ...

That's reassuring given that one of my tasks this afternoon was to get the kitchen heater going. It's a sort of central heating-powered fan heater. There are clear instructions inside to insert a BS1362 fuse in the supply. The motor, all 20-odd watts of it, had fallen apart again. I am now reassured to know that next time it falls apart, the kitchen will not be engulfed in flames.


The same cannot be said when my Mrs P is cooking. ???

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Thanks Weirdbeard that link was enlightening. There's nothing new under the sun.


Z.

You are welcome best wishes x :)


 

Indeed - the circuit goes all the way back to the sub-station after all. So your one of your circuits is protected by one fuse, a B6, maybe a submain protective device, the DNO's fuse etc (perhaps some of those devices rely on an upstream device for backup protection). While the other circuit is protected a different fuse, then the same B6 etc. Hence the two circuits aren't entirely protected by the same devices.

   - Andy.

We are talking about a simple domestic situation. The fan L and switched L both originate from one B6 or B10. There are not two separate supplies. I am only concerned with matters within the installation not without it, such as the final circuit and not beyond. 110.2 (1).


Z.


 

Weirdbeard:

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Thanks Weirdbeard that link was enlightening. There's nothing new under the sun.


Z.

You are welcome best wishes x :)


 

The video clip that I posted details of previously in this thread showed a P.C.B. fuse inside the fan unit. That is good. I think that 250mA ceramic fuses could be used which would operated more efficiently under fault conditions. That and a thermal fuse in the motor windings  as well. A 3 Amp fuse will not prevent a fire even if it is asked for by the manufacturers.


Z.


Z.

Zoomup:

We are talking about a simple domestic situation. The fan L and switched L both originate from one B6 or B10. . . 

As you have two fuses supplying your fan via its supply cable, you have dual supplies to the unit. The definition of a “circuit” will apply to each of your fuses. This would be considered dangerous in a commercial environment as it would not be expected, and would be labelled as being fed from two supplies. In a domestic environment it is equally dangerous, perhaps more so. It should be labelled as having dual supplies, or fed from a single fuse located before the light & switch as others have said. 


Regards,


Alan.