Over-run extractor to come on same time as shower

[mattthespark]

Gents,

I want an over-run extractor fan to come on when the shower pull cord is pulled on, then run on for a timed period after the shower pull cord is 'pulled off' (snigger snigger).

My solution:

The shower circuit is currently run in 10mm t&e. Take a 10mm t&e feed off the permanent live & permanent neutral (ie the feed to the shower isolator), plus a 10mm feed off the switched live (ie the load live at the shower isolator). Bring these three conductors to a db, and fuse down the lives to 6a via two mcb's (one each for the perm live and the switched live). Then take a 1mm 3 core out of the db (two lives via the breakers, the neutral connected directly to the incoming 10mm neutral) to the over-run extractor fan - first stopping off at a triple pole isolator.

Sound safe / within regs?

Any advice would be greatly appreciated. Many thanks.

 

[ban-all-sheds]

Sounds like a lot of faffing about with junction boxes for all those 10mm² conductors, because you'll not get 2 into each shower switch terminal.

Why not put a flow switch in the water supply to the shower?

Or use a pull switch to control the fan and a contactor which switches the shower supply?

Or use a fan with a humdistat?

 

[mattthespark]

Thanks - useful comments and ideas. All three solutions easier than mine to lesser or greater extent!

Will suggest a remote humidistat to my client. Cheers.


Out of interest, was my original solution safe / to the regs? Just out of interest.

 

[LoveRocket]

Yes, it is safe and compliant, just incredibly impractical - there is no way on earth that you'd get two 10mm2 cores in to a terminal on a shower or DP switch.

You could have taken the 1mm cable straight from the DP switch terminals, you are allowed a couple of meters before fusing down when changing cable size (I think)

PS. Great use of the phrase "pulled off"!

 

[Lectrician]

I like the flow switch in the water line - we have connected many of these up on commercial sites.

 

[ColJack]

nevermind, just noticed BAS already suggested the contactor idea..

 

[Spark123]

Out of interest, was my original solution safe / to the regs? Just out of interest.

No it isn't as you have the fan fed from two separate overcurrent protective devices and a shared neutral.

 

[ban-all-sheds]

1) If the fan was on a lighting circuit in traditional style, and the MI to fuse it at 3A was done with 2 FCUs, one in the permanent live and one in the switched, would you object? Which regulation would be broken?

2) It's not a shared neutral.

 

[Spark123]

I have never done it like that, nor have I seen an MI allowing that hence imo it will not comply with 134.1.1.
Last time I had this problem I fused the lighting circuit down to 3A for the bathroom with a FCU above the door and a 3 pole isolator adjacent for the fan.

My solution:

The shower circuit is currently run in 10mm t&e. Take a 10mm t&e feed off the permanent live & permanent neutral (ie the feed to the shower isolator), plus a 10mm feed off the switched live (ie the load live at the shower isolator). Bring these three conductors to a db, and fuse down the lives to 6a via two mcb's (one each for the perm live and the switched live). Then take a 1mm 3 core out of the db (two lives via the breakers, the neutral connected directly to the incoming 10mm neutral) to the over-run extractor fan - first stopping off at a triple pole isolator.

The way I am reading it will result in having a 3 core 1mm cable fed from a pair of 6A breakers. The neutral is shared between the two circuits hence a shared neutral.

 

[GaryMo]

1) If the fan was on a lighting circuit in traditional style, and the MI to fuse it at 3A was done with 2 FCUs, one in the permanent live and one in the switched, would you object? Which regulation would be broken?

The installation of a FCU is a new distribution point and it's not unreasonable for the outgoing circuit to have a separate schedule of test results from the rest of the circuits being fed from the main consumer unit.
When you have two overcurrent protective devices supplying a single piece of equipment then you know yourself that it's just plain wrong and rough as a badgers backside.

Look at THIS for an example of a Vent Axia VA100 and note where they expect the overcurrent protection to be placed.

 

[Spark123]

I also imagine that bridging the shower isolator with an electrical appliance will mean it is no longer an effective means of isolation.

 

[ColJack]

1) If the fan was on a lighting circuit in traditional style, and the MI to fuse it at 3A was done with 2 FCUs, one in the permanent live and one in the switched, would you object?

yes.. the FCU should be placed in the permanent live before it reaches the switch, thus protecting the permanent live and the switched live.

Which regulation would be broken?

I've an incling that 431.1.1 applies.
It mentions 3 phase motors as ONE example where danger can arise from the disconnection of just one line conductor, but I put it to you that if one fuse or breaker operates on one conductor ( or is switched off ) then it's dangerous in as much as a general DIYer might think that it's safe to start fiddling in there without realising that the other line may still be live.
simplest solution since we're talking breakers is to use a 2 pole breaker.

2) It's not a shared neutral.

2 line conductors exit 2 different OCPD's and return on only one neutral..
that is the very definition of a shared neutral..

 

[LoveRocket]

Feeding the bathroom lights AND a fan from an FCU on the lighting circuit? The whole point of the FCU is so that a knackered fan doesn't take out the lighting circuit (although in reality a 3a 1361 ain't gonna discriminate well against a B6)

So you've got the lights and the fan both on the FCU, the fan seizes and the lights go out. Brilliant.

There is absolutely no need whatsoever to fuse down a switched line from a lighting circuit.

 

[GaryMo]

There is absolutely no need whatsoever to fuse down a switched line from a lighting circuit.

There is if you want to comply with the Manufacturers Instructions and in turn, BS7671.

A knackered fan may well take out the local lighting circuit whether there's a 3A BS1362 fuse protecting the fan and local lighting circuit or not.

 

[ColJack]

never said there was a need..
it's the MI instructions that do, and it's nothing to do with keeping the lights on..
they don't know if you're feeding the fan from the lights or a spur of a ringmain.. so they want it fused suitably to protect the fan.. 6A should do fine..