Bathroom downlighters

or that a S/L-N fault may occur upstream of the resistor.
That won't result in an overload, though, will it?
Well, it would certainly result in an over-current! - are you talking about the terminology?
No, we normally assume that a 3A fuse is required to save the fan or its wiring should the motor jam - overload - because it is (poorly made and) not fitted with an integral fuse.

A SL-N fault upstream of the resistor, as you have suggested, would result in a short-circuit resulting in ADS of the (6A?) MCB.
 
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No, we normally assume that a 3A fuse is required to save the fan or its wiring should the motor jam - overload - because it is (poorly made and) not fitted with an integral fuse.
Well, I think we assume that it is 'required' to protect the fan or its wiring should 'something' (less than a 'dead short') happen within the unit to increase current drawn. A jammed motor is undoubtedly the most likely cause of that. Having said that, I've had a good few 4" extractors 'jam up' over the years - and no OPD has ever operated, and nor has there been any smoke or flames - IIRC, they just 'get a bit warm'!
A SL-N fault upstream of the resistor, as you have suggested, would result in a short-circuit resulting in ADS of the (6A?) MCB.
If it's a full-blown 'negligible impedance' fault, then yes, but 'they' may be thinking of a lesser degree of S/L-N 'fault' than that. It's obviously all silly - in sensible terms, the S/L does not need fusing (and, come to that, nor probably does the permanent L!).

Kind Regards, John
 
I'm under no illusion that they'll be gas-tight, but I simply can't see that there will be a significant moist-air flow through them. Should I be worrying?
Water vapour is a gas.


There is no insulation above the bathroom ceiling because the cold water tanks are above it.
You've got cold water tanks the size of the bathroom?
 
The light fittings have very strong springs which pull them tightly against the ceiling when released, although I'm sure the seal is not airtight.
Then you'll get warm moist air entering the loft where it will cause condensation.

Maybe not enough to cause you problems - how long do you plan to stay there?


Should I use an additional bead of fire retardant sealant to ensure a good seal?
It doesn't need to be fire retardant, and if it's an intumescent substance it won't swell up and seal anything unless there's a fire.
 
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As he said, because of their history, BAS still tends to think of downlights as 'spotlights' (i.e. narrow beam angle)
Actually I said they are often known as spotlights. Which they are.


and seems to overlook the fact that bulbs/lamps with wide beam angles are now available.
As you observe, if these lights were designed to provide general room illumination then the OP would not need 8 of them.


If your bulbs really do give a 120° beam angle (with the fittings you are using) then, assuming the ceiling is at about 2.4m, just one of those would illuminate a circular area of about 8.3m diameter at floor level,
Would that circle be uniformly lit?
 
As he said, because of their history, BAS still tends to think of downlights as 'spotlights' (i.e. narrow beam angle)
Actually I said they are often known as spotlights.
You did - but it was indicative of your ongoing way of thinking.
Which they are.
I don't think any sensible person would describe a light with a beam angle of 120° as a 'spotlight' (at any significant distance, it would be a mighty big 'spot'!).
As you observe, if these lights were designed to provide general room illumination then the OP would not need 8 of them.
I don't believe that he does need 8.
If your bulbs really do give a 120° beam angle (with the fittings you are using) then, assuming the ceiling is at about 2.4m, just one of those would illuminate a circular area of about 8.3m diameter at floor level,
Would that circle be uniformly lit?
I don't know. Obviously not 'perfectly uniform', with "100% illumination" at 8.300000m and "zero illumination" at 8.300001m, but I suspect it's not appreciably less uniform than any other light source with a 120° beam angle.

Kind Regards, John
 
I'm under no illusion that they'll be gas-tight, but I simply can't see that there will be a significant moist-air flow through them. Should I be worrying?
Water vapour is a gas.
Well of course it is. However I can't see that there would be any more moist air flow through/past these fittings than there would through a traditional bathroom light (and its wiring hole).

There is no insulation above the bathroom ceiling because the cold water tanks are above it.
You've got cold water tanks the size of the bathroom?
It is a small bathroom, and a low loft, so there are three cold water tanks and the hot water expansion tank all above the bathroom. Strictly they are only half the width of the bathroom, but that width includes all the places lighting would sensibly go.
 
I've re-read the fan installation instructions. Interestingly (?) they show the switched live taken off after the downfuse/isolater. So that effectively leaves the switched live also downfused.

But, it also means that if, as seems to be the norm, the fan is switched with the light then the fan isolator would also have to isolate the light. If so, for fans fitted in the bathroom, there isn't the convenience of being able to maintain the fan with the light on, making the isolator pointless - you may as well switch off the entire lighting circuit.

Or, if the switched live and lighting are not after the isolator, then the isolator gives a false sense of security as the switched live at the fan will be live if the light is on, even if the isolator is used.

Or is there something wrong with my logic here?
 
I've re-read the fan installation instructions. Interestingly (?) they show the switched live taken off after the downfuse/isolater. So that effectively leaves the switched live also downfused. ... But, it also means that if, as seems to be the norm, the fan is switched with the light then the fan isolator would also have to isolate the light. If so, for fans fitted in the bathroom, there isn't the convenience of being able to maintain the fan with the light on, making the isolator pointless - you may as well switch off the entire lighting circuit.
Indeed - which is why that is not a very common way of doing it. There is an alternative approach which uses a double pole light switch - one pole then switches the ('fused') live to provide the S/L for the fan, whereas the other pole just switches the usual 'unfused' live for the light. You may be getting confused by talking about the "downfuse/isolator" - if one wants 3-pole isolation, they will inevitably be two different things.
Or, if the switched live and lighting are not after the isolator, then the isolator gives a false sense of security as the switched live at the fan will be live if the light is on, even if the isolator is used.
See above. To be useful/safe, the (3-pole) isolator obviously has to isolate all conductors going to the fan, regardless of which are and are not fused.

Kind Regards, John
 

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