Extractor fan from shower isolator

[Pretty Mouth]

I came across this today when changing a shower isolator that was stuck in the on postition.

40A Hager RCBO feeding 10mm² twin + earth to a pull cord shower isolator. On the load side of the isolator there was 10mm² going off to the shower as you would expect, but also from the isolator was 2.5mm² T+E feeding a 3A fused spur in the loft, which then fed an extractor via 1.5mm² T+E.

So the extractor is switched on and off with the isolator, along with power to the shower. Not very good practice IMO, but is it compliant?

I believe so: the 2.5mm² and 1.5mm² T+E should be protected from overload by the 3A fuse. PFC was about 1100A, so the requirements of the adiabatic equation should be met. RCD protection means disconnection times are met.

What do you guys and girls think?

 

[James]

My biggest concern is that the fused spur is in the loft and may not be accessible.

 

[Pretty Mouth]

My biggest concern is that the fused spur is in the loft and may not be accessible.

I hadn't considered that. Actually one of the better lofts I've been in - loft ladder, boarded out, and with a light. But you think it would be a reg breaker had it been under 12" of itchy stuff?

 

[James]

Switches and protective devices should be accessible.
Partly for safety to turn off in emergency
Mainly for convenience though.

 

[Julie.]

Don't see an issue really, just a bit unusual, I have come across this before, my own house has underfloor heating in an en-suite shower that is fcu'd off the shower itself.

Got busy with my calculator when I found out, everything was ok disconnection times, adiabatics etc

There is the issue of circuits not being as independent as I would have liked, but other than that...

 

[Wilko]

If there is an external window in the bathroom then building regs are satisfied too, if I recall correctly.

 

[LastManOnline]

I hadn't considered that. Actually one of the better lofts I've been in - loft ladder, boarded out, and with a light. But you think it would be a reg breaker had it been under 12" of itchy stuff?

The insulation is, nt an issue as both the 2.5 and 1.5 will never be carrying more than the fan load. The 3 amp fuse is well below what the regs allow for cables of those sizes embedded in insulation. In practice however it would be better to connect the fan to the light. I personally like to wire the fan back to the switch and allow the customer the option of switching the fan separately

 

[westward10]

The insulation is, nt an issue as both the 2.5 and 1.5 will never be carrying more than the fan load. The 3 amp fuse is well below what the regs allow for cables of those sizes embedded in insulation. In practice however it would be better to connect the fan to the light. I personally like to wire the fan back to the switch and allow the customer the option of switching the fan separately

They will under fault conditions prior to the spur.

 

[LastManOnline]

They will under fault conditions prior to the spur.

Correct. But is, nt that a "risk" you already accept in practice in the UK?. For instance with your unfused spur outlet and the "3 Mt rule"?

 

[westward10]

Correct. But is, nt that a "risk" you already accept in practice in the UK?. For instance with your unfused spur outlet and the "3 Mt rule"?

No the cable must be able to withstand fault current.

 

[DPG]

The problem I see is that the extractor is being switched on and off, probably every day, by use of the shower isolator. The isolator should not be used like this.

 

[Vortigern]

Separation of circuits as required by BS7671. Put it on the light circuit? How does the three pole isolator work within that for maintenance?

 

[Flanders]

Sounds to me that the prisable is a good idea .The main time you need the fan on is when the shower is on . If there is a window in the room you would not need the light on to have a shower, so if the fan was controlled by the light switch it may not be used. Much better that the fan comes on when the shower is in use. I have seen similar sets up with cooker extract fans connected to the outgoing side of a cooker switch. So the fan comes on when the cooker is turned on.

 

[DPG]

Sounds to me that the prisable is a good idea .The main time you need the fan on is when the shower is on . If there is a window in the room you would not need the light on to have a shower, so if the fan was controlled by the light switch it may not be used. Much better that the fan comes on when the shower is in use. I have seen similar sets up with cooker extract fans connected to the outgoing side of a cooker switch. So the fan comes on when the cooker is turned on.

But the shower isolator shouldn't be used as a functional switch for the fan.

 

[James]

But the shower isolator shouldn't be used as a functional switch for the fan.

Why not?