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

[PaulDun41]

What size cable for 2 extractor fans in a public toilet?

 

[buzzlightyear]

are you a spark?

 

[PaulDun41]

are you a spark?

Yes, just asking the question

 

[James]

Total circuit load in amps?

 

[westward10]

Your opening question is somewhat bizarre if you are a qualified electrician.

 

[MJPD29]

Yes, just asking the question

It seems rather basic

 

[Soi disant]

What size cable for 2 extractor fans in a public toilet?

One with a current carrying capacity greater than or equal to the rating of the breaker, with low enough impedance to ensure disconnection times are met and voltage drop is not too high, and greater than or equal to the load, which in turn should be less than or equal to the rating of the breaker.

Of a type suitable for the conditions where installed.

 

[James]

One with a current carrying capacity greater than or equal to the rating of the breaker, with low enough impedance to ensure disconnection times are met and voltage drop is not too high, and greater than or equal to the load, which in turn should be less than or equal to the rating of the breaker.

Of a type suitable for the conditions where installed.

Technically correct but somewhat unhelpful

 

[timhoward]

What size cable for 2 extractor fans in a public toilet?

Be careful mate. This is a public environment where literally anyone can come into contact with this work, and your neck is on the line as the bloke that installed it.
In the nicest way possible, if you need to ask this you shouldn't put yourself in the firing line.

 

[PaulDun41]

Be careful mate. This is a public environment where literally anyone can come into contact with this work, and your neck is on the line as the bloke that installed it.
In the nicest way possible, if you need to ask this you shouldn't put yourself in the firing line.

Thanks mate, I was just asking as someone’s done it and debating if they had installed the correct cable?

 

[timhoward]

Thanks mate, I was just asking as someone’s done it and debating if they had installed the correct cable?

That wasn't very clear from the question!
So you are saying it's currently 20 amp RCBO with 1.5mm 3 core.
Are there any fused isolators for the fans or are they connected directly?

 

[Mike Johnson]

Total circuit load in amps?

Most domestic fan manufacturers require a 3amp inline fuse for their extractors and its normal to have a three pole isolation switch, one assumes this is in a work environment, therefore industrial/commercial?

 

[timhoward]

At the moment my only answer is that no installation method of 3 core flat PVC 1.5mm cable is rated for 20 amps. I was wondering if there were FCU's by the fans and that overload protection was provided that way.
It's likely the RCBO is oversized but can't be sure without knowing more about the fans who knows.
If the OP has a clamp meter it would be interesting to know the current draw with both fans on.

 

[Soi disant]

At the moment my only answer is that no installation method of 3 core flat PVC 1.5mm cable is rated for 20 amps.

Method C.

 

[LastManOnline]

Method C.

Strictly speaking method C is 19.5 amps. But we won't haggle over 0.5 of an amp. In fact running a 1.5mm directly to the 2 fans is also perfectly safe on a 20amp rcbo. But is it conventional, good practice or advisable? No

 

[timhoward]

Strictly speaking method C is 19.5 amps. But we won't haggle over 0.5 of an amp. In fact running a 1.5mm directly to the 2 fans is also perfectly safe on a 20amp rcbo. But is it conventional, good practice or advisable? No

Is it not 17.5 amps for a 3 core or am I losing plot again?!

Table 4D2A:

 

[Soi disant]

Strictly speaking method C is 19.5 amps.

Not according to 4D5

 

[LastManOnline]

I was wondering if there were FCU's by the fans and that overload protection was provided that way.

If the rcbo feeds the fans directly than they can be treated like any "End of line" appliance and overload protection omitted. Short circuit protection only required and the 20 amp RCBO covers that

It's likely the RCBO is oversized but can't be sure without knowing more about the fans who knows.

It would be oversized if the 1.5mm was connected to a circuit where the loading can't be controlled directly, like a socket circuit socket

If the OP has a clamp meter it would be interesting to know the current draw with both fans on.

In principle that's not an issue. Both fans won't take more than an amp or 2.Well under the capacity of the cable and the rcbo. 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!!

 

[Soi disant]

Is it not 17.5 amps for a 3 core or am I losing plot again?!

That's 3-core as in 3 phase conductors, not as in T&E.

 

[LastManOnline]

Is it not 17.5 amps for a 3 core or am I losing plot again?!

Table 4D2A:

View attachment 84376

You are most definately not losing the plot. It's there in black and white (or purple and white). But I think the key is that that 3 core is referring to 3 "loaded" conductors, as in 3 phase, whereas the 3 core referred to by the OP is containing just 2 loaded conductors

 

[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.?

 

[Mike Johnson]

The requirement for a 3amp inline fuse in the UK is generally from the manufacturer, not a regulation.

 

[Soi disant]

The requirement for a 3amp inline fuse in the UK is generally from the manufacturer, not a regulation.

Indeed.

So why do they require that in the UK when they don't require it in other countries?

As I said

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?

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?