Shower/Fan Ceiling Switch

[alanellicott]

I have just replaced a 9.5kw shower with another 9.5 KW shower (triton) and I initially noticed that the pull switch on the ceiling was having difficulty "engaging". By this I mean that I had to pull the switch a few times before the red light would come on even though the bathroom fan would come on.
After using the shower for about 10 minutes something overheated in the switch and it blew quite dramatically and also caused the main fuse on this single curcuit to go as well.
Clearly the new shower plus the fan is taking more current than the switch can cope with so I need to upgrade.
As I have lost the rather complicated wiring diagram for the fan, I have decided to wire the shower and fan separately on two separate pull switches.
Can anyone tell me what ampage ceiling switch would be suitable for a 9.6kw shower? I am sure the existing one was 45 amp and also what main fuse size would be required for a 9.5kw shower plus small domestic ceiling fan. Yes we are still on fuse wire here!

 

[PrenticeBoyofDerry]

45A pull cord isolator for shower

The shower will demand 41A, so ideally 45A or 50A MCB.
Showers should be on an independent circuits, without other equipment installed.
So I suggest the fan is connected to the light circuit.

 

[alanellicott]

Many thanks. Makes a lot of sense.
I guess the ceiling fan would be quite low wattage so it must have been the shower that pushed the switch over the edge. I think the fan will be happy on a 5 amp circuit.

 

[PrenticeBoyofDerry]

Many thanks. Makes a lot of sense.
I guess the ceiling fan would be quite low wattage so it must have been the shower that pushed the switch over the edge. I think the fan will be happy on a 5 amp circuit.

Ex-fans normally 20W, so draw a lot less than 1A, it's possible that a loose connection caused your problem. But showers should run on dedicated circuits without any other current drawing equipment connected.
I suggest when you install new pull cord, that you seal cable entry hole to prevent dust and debris falling from ceiling, this in my experience often leads to the switch mechanism jamming. Silicon will do the job.
Link to wiring fan to light //www.diynot.com/wiki/electrics:lighting:fan

 

[ban-all-sheds]

The shower will demand 41A

I can pretty much guarantee that the 9.5kW rating is at 240V, not 230.

Showers should be on an independent circuits, without other equipment installed.

That's not the issue - there's no intrinsic reason why any radial circuit should not supply any collection of equipment. The problem here would have been that (again another 99.9999% guarantee) the cable from the switch to the fan would not have been the correct size.

 

[alanellicott]

I have now purchased a new 45 amp ceiling switch and wired it up without the fan for the moment and I have a problem.
I switched the shower on and ran it at full heat (This is a 9.7 kw) shower and after about 5 minutes the supply side wiring (both live and neutral) both started getting hot - but not too hot to touch. I ran it for about 10 minutes and it didn't seem to get any hotter.
I am 100% sure the cable is 6 mm as it is very much heavier than 2.5 mm and I don't think there is a size in between. Comparing it to 2.5 mm it is almost double the short width and one and a half times the long width and both red and black being made of 7 strands which are only marginally smaller than the single strand of a 2.5 cable.
Do you expect wiring on showers to get warm? None of it is in conduit but I am a little worried. Why just the supply and not the load side. Should I perhaps upgrade to a 50 watt switch?

 

[alanellicott]

Sorry meant amps not watts re 50 amp switch

 

[AdamCH]

I am 100% sure the cable is 6 mm as it is very much heavier than 2.5 mm and I don't think there is a size in between.

You can get 4mm. Personally I'd get someone to take a look at the shower & see what's wrong. You don't want a fire.

 

[EFLImpudence]

The shower will demand 41A, so ideally 45A or 50A MCB.

Naughty PBoD.

The 9.5kW will be quoted by the manufacturer at 240V and so is 39.6A

At 230V it will be 8.74kW and so 38A.

 

[EFLImpudence]

Cable sizes

 

[alanellicott]

Thanks for the link to the cable sizes chart.
Definitely 6mm2 as outer cover is over 13mm * 7mm +

I have read elsewhere that shower cables can get warm so could they be OK?

 

[alanellicott]

I'm getting the hang of this forum now and my problem is evidently not unique and there are lots of discussions.
I realise I am only trying to convince myself that I don't need to replace the 6mm with 10mm as that would require re-tiling part of the bathroom!!!
But........ I have now run the shower for a good 20 minutes and the cables get hot but not burning hot. I have read that <70C is OK but that sounds VERY hot so not sure about that. Most of the run is exposed to the air - either surface mounted or clear of rockwool. None is in conduit.
If you go back to the beginning of this thread you will see that I have always had a 9.7kw shower on this circuit and I may have had warm cables and not known it for years. I believe the original problem with the pull switch melting was because of a loose terminal connection.
So.... I have a 45 amp fuse in place. Would that go before the wiring caught fire.
I'm risking some flack here aren't I?

 

[EFLImpudence]

As long as the 6mm² cable runs through NO thermal insulation or conduit it will be fine.

Also a 40A mcb IS adequate although if you already have a 45A fitted that will be alright.

That is presumably why the shower is made to 9.5kW @ 240V - just under 40A.

 

[alanellicott]

As long as the 6mm² cable runs through NO thermal insulation or conduit it will be fine.

Also a 40A mcb IS adequate although if you already have a 45A fitted that will be alright.

That is presumably why the shower is made to 9.5kW @ 240V - just under 40A.

Am happy now. I have just redone the terminal connections and done another test running it at 9.7kw for 20 minutes and have hardly (if anything) warming taking place. I reckon I had a bad (reduced) connection before. But just as an extra precaution I am going to invest in a 40amp MCB tomorrow as we are still on fuse wire here. Thanks to everyone for their advice

 

[EFLImpudence]

Ah. That would be advisable. Do you mean the plug-in ones like THIS ?

If a rewirable fuse is used the cable's current carrying capacity should have been derated by 0.725 which would result in it not being suitable.
It will be alright with the mcb.