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