Information required about fused switch-boxes and alternatives to these.

[Lucky Luke]

Now I'm confused. I understood you wanted a backbox you could screw to the wall, feed the flex in at the top & out at the bottom and onwards to the fan. You don't have to have a metal backbox set in the wall, a plastic surface box is perfectly acceptable. The glands are to provide strain relief to the flex ( you wouldn't usually use them with installation cable since the cables are held in place by clips or plaster)- you remove the knockouts top and bottom of the backbox, insert the gland and then thread the cable through the gland.
In all this, we've all ignored the fact that you're in a bathroom so zones apply- your new FCU would have to be at least 600mm from the bath/shower OR more than 2250 above floor level

O.b.n.d. Sorry — I didn't know that there were such things as plastic surface boxes, to back the switch pattress that you alerted me to. If these back-boxes are of universal size, I suppose the problem would be solved. I shall now investigate, and decide whether Terry's solution, or yours, is the way to go. Thanks very much, friend, and to all who have contributed. Well, this is a great relief to me! It's surprising how ignorant one can be.
A.W.

 

[oldbutnotdead]

O.b.n.d. Sorry — I didn't know that there were such things as plastic surface boxes, to back the switch pattress that you alerted me to. If these back-boxes are of universal size, I suppose the problem would be solved. I shall now investigate, and decide whether Terry's solution, or yours, is the way to go. Thanks very much, friend, and to all who have contributed. Well, this is a great relief to me! It's surprising how ignorant one can be.
A.W.

Think we've both given you the same solution. Have fun

 

[Lucky Luke]

I understood you wanted a backbox you could screw to the wall, feed the flex in at the top & out at the bottom and onwards to the fan. You don't have to have a metal backbox set in the wall, a plastic surface box is perfectly acceptable.

I'm sorry, my friend — I didn't know that plastic back-boxes could be bought to fit the switched pattress on. I thought they needed a metal box sunk in the wall. It seems, then, that my problem is solved! Thanks to everyone that replied. It's all greatly appreciated. I posted this reply (or one very much like it) about five hours ago. I don't know why it was not posted.
A.W.

 

[DetlefSchmitz]

It was!

 

[SimonH2]

If these back-boxes are of universal size ...

They are, and "mostly" any (single) accessory from any manufacturer will fit any (single) back box from any manufacturer - but there are some oddballs where it can be tricky.
But while they are a standard size, there are differences in styling - mostly in corner radius - and fitting an accessory that doesn't match the backbox (or vice-versa) can look a bit cack. Ie, if you have a backbox with nice rounded corners and the accessory has "sharp square" corners, then the accessory will stick out a little on the four corners.

 

[ericmark]

You can get in line fuses and fuse boxes, but most are designed for extra low voltage not 230 volt, there are rules on clipping cables and ensuring cables can't be pulled out of the box so be it a stuffing gland or a clamp you need some thing to secure the cable, so a Fuse connection unit in a back box could in theory be left free but I would always fix it to some thing. Odd there are loads of in-line RCD's

But you can't seem to get a MCB or fuse to use in line which is 230 volt rated.

 

[ban-all-sheds]

I'm sorry, my friend — I didn't know that plastic back-boxes could be bought to fit the switched pattress on.

Box Ξ pattress, pattress Ξ box.

https://www.bing.com/images/search?q=pattress

 

[EFLImpudence]

Yes, isn't that what the OP must have seen, and had in mind, when repeatedly talking about a "standard fused switch-box", thinking they were one piece?

Pattress

Switched Fused Connection Unit

Ceiling Roses