What cable size and breaker would I need for two extractor fans in a public toilet? 1.5mm 3 core and a 20amp rcbo?

[LastManOnline]

Not according to 4D5

Does it not say 19.5 amps in the table "Tim Howard" posted?

 

[Soi disant]

Does it not say 19.5 amps in the table "Tim Howard" posted?

It does, but that's Table 4D2A, not 4D5

 

[timhoward]

The issue is, is the cable going to be protected properly under overload and short circuit conditions. It is Interesting how unconventional situations (like the OP, s) force us to look at a situation that we all know is instinctively wrong but can't immediately explain why (talking about myself here). Then we end up "going back to the drawing board" and having to figure out again.. "Why is this wrong?". Good exercise though!!

Thank you for talking that through. I was certainly thinking in terms of overload and fault protection. I get that overload protection could technically be omitted. If (as in the case of many fans) the manufacturer advises 3 amp protection it still doesn't sit right with me that that 60 amps could theoretically flow (B curve) before it shuts off.
Is there a remote possibility of more current being drawn if the if the fan jammed or the windings were damaged and it failed to properly start and just hummed I wonder. Probably unlikely and academic.

 

[timhoward]

It does, but that's Table 4D2A, not 4D5

My bad - trouble with using app, too easy to choose wrong table.

 

[LastManOnline]

It does, but that's Table 4D2A, not 4D5

Then I stand corrected. I was, nt aware you had different tables for calculating current capacity.

 

[Soi disant]

Then I stand corrected. I was, nt aware you had different tables for calculating current capacity.

There are different cable types, so there have to be different tables.

 

[LastManOnline]

Is there a remote possibility of more current being drawn if the if the fan jammed or the windings were damaged and it failed to properly start and just hummed I wonder. Probably unlikely and academic.

That's a valid point actually as technically all motors should have overload protection. But the wattage of a standard 4" fan is very low.Should it jam its internal impedence will prevent large currents from flowing and if they did the fan windings would likely burn out long before the supply cable would be troubled. In fact you will sometimes come across fans that have "stuck" and on being released they carry on working. High internal impedence prevents the from burning out

 

[Soi disant]

Do they make special fans for the UK, different from the millions they make for countries where you can't get any overload protection beyond the circuit OPD?

 

[LastManOnline]

There are different cable types, so there have to be different tables.

Interestingly 4D2A conforms exactly with the table we use here (ROI) for pvc insulated cables

 

[Soi disant]

Ah - here they reverse-engineered 4D5 to keep 2.5mm² 32A ring finals workable. ?

 

[LastManOnline]

Do they make special fans for the UK, different from the millions they make for countries where you can't get any overload protection beyond the circuit OPD?

That is a very good question actually. I think it has less to do with the type of fan and a little more to do with the " fuse culture" in UK (and ROI). The only place (usually) you will find fuses in the continent is at the CU. Of course in UK you are obliged to have 13 amp fused plug tops because of the 32 amp ring circuit. But sometimes you also install fuses for convenience. We may for instance install several FCU, s on a circuit for small appliances whose purpose is to ensure one faulty appliance does, nt take the whole circuit out

 

[westward10]

The reason some manufacturers suggest a 3A fuse is for fire protection so should the fan seize then the theory is the fuse will rupture before the windings overheat and catch fire. There was a study I found online but can't find now where this was put to the test and the success of the 3A fuse was dependent on the manufacturer, some worked whilst some did not.

 

[LastManOnline]

The reason some manufacturers suggest a 3A fuse is for fire protection so should the fan seize then the theory is the fuse will rupture before the windings overheat and catch fire. There was a study I found online but can't find now where this was put to the test and the success of the 3A fuse was dependent on the manufacturer, some worked whilst some did not.

Good comment and new information for me. I must be honest and say I have never installed a 4 " fan that required an inline fuse. I have also not come across them over here (yet). However I must also say I have at times replaced fans without rigidly reading every word in the instruction manuel so that is a good reminder for me

 

[Soi disant]

The reason some manufacturers suggest a 3A fuse is for fire protection so should the fan seize then the theory is the fuse will rupture before the windings overheat and catch fire.

So are they selling us different fans to the ones they sell in countries where, short of a dedicated circuit, you can't put them on a 3A fuse?

 

[westward10]

So are they selling us different fans to the ones they sell in countries where, short of a dedicated circuit, you can't put them on a 3A fuse?

No idea what you are getting at.

 

[Soi disant]

No idea what you are getting at.

If I go to Mr.Bricolage and buy a ventilateur de salle de bains, 'cos Iive in France, I'm not going to be able to put it on a 3A fuse, am I?

 

[Mike Johnson]

No under the French regulations you will have to put it on an independent 6amp MCB.

 

[Soi disant]

OK - so it goes on a 6A, like millions of fans here on lighting circuits.

Are the multinational fan makers producing different products for here, such that our 6A circuits won't do, but French ones will?

 

[Mike Johnson]

OK - so it goes on a 6A, like millions of fans here on lighting circuits.

Are the multinational fan makers producing different products for here, such that our 6A circuits won't do, but French ones will?

I have no idea what you are asking?

 

[LastManOnline]

I have no idea what you are asking?

He is asking why would a fan suitable for a 6amp protected circuit in France not be suitable for a 6amp protected circuit in the UK?. Why the requirement for a 3 amp inline fuse in UK?. Unless it is of course a different type of fan being installed in the UK.?