Electrical and ventilation questions for cloakroom

[Andy Hall]

For my cloakroom project, I am pondering on a few electrical and other questions:

At present there is a central ceiling rose which has a lighting circuit looping through it. In the conventional way, a pull cord switch is connected to this and there is a separate feed of permanent and switched phase, neutral and earth going to the ventilation fan.

To provide a little detail, the room is rectangular with the door at one end of the long side. The ceiling joists run parallel to the long dimension. The ventilation fan is towards one end of the room and central and has a duct to deliver the exhaust air a few metres to the edge of the house.

There is not easy access from above, so work will have to be done from below. I would prefer to minimise repair work on the ceiling plasterboard.

At one end of the room, further from the door, the throne will be installed with concealed cistern covered with small granite shelf. Above this, with a space for whatever, will be a wall cupboard which will go to a height of about 200mm below the ceiling.

The intention is to do away with the ceiling rose and pull switch and re-route the wiring to run on the walls. There will be a plate switch inside the door, from which cable will run horizontally to the corner. From there it will run vertically in the 150mm allowed space, behind the cupboard, to the space above it.

Ideally, I would like to run a new cable from the existing ceiling rose position, across the ceiling, above the plasterboard, drop it down above the cupboard and make connections there.

This raises two questions:

1) In effect, this creates a spur - i.e. the daisy chain of the lighting circuit comes to the ceiling rose position and the cable to feed the lighting circuit to the edge of the room above the cupboard would be teed from it. I suppose that I could run two cables and effectively maintain the daisy chain. I can't find any rules on this in BS7671 one way or the other.

2) I need a solution for jointing the cables at the ceiling rose position. Crimps are the obvious choice since the hole will be repaired and covered. However, I could do with a solution to provide the second required level of insulation etc. Conventional junction boxes don't seem very suitable because of the screw terminals, although I suppose those could be removed; but also I don't really want to make the ceiling hole larger if I can help it. Is heat shrink tube permissible in this application to provide the second layer of insulation? Any other ideas?

Ventilation:

3) I want to move the fan from its current ceiling mount position to being fitted above the cupboard. There would then be a removable grille above the cupboard. The idea is to make the ceiling clear, and I should be able to reduce the noise of the already quiet Vent Axia fan even further. I can't find any Building Regulations objection to so doing. Anybody know different?

4) I believe the Buiding Regulations specify that the fan comes on when the light is switched on and should run for a period of time after it has been switched off. However, I am intending to have two sets of lights; one being under-cupboard and the other some downlighters on the long wall or wall lights. So the question arises of whether the fan should come on when the "main" light is switched on or when either is switched on. Obviously I could do the latter with relays.

Comments?

[John Rumm]

Since the lighting circuit is a radial there is no actual requirement for it to follow a linear progression from one light to the next. You can split it any which way you find convenient - taking "spurs" or adding branches when you need.

IIUC heat shrink is acceptable in this case (it would be acceptable for jointing a cable that you then buried in plaster, so entombing it in the ceiling void should not be a problem).

Can't think of any reason why not.

I would go with the "main" light only. The also gives you an easy option for circumventing the starting of the fan on any occasion that you wish to so do. (which building reg were you thinking about BTW?)

[Andy Hall]

That was my thought as well. I couldn't think of any reason to follow a particular pattern - the lighting circuits are protected by 6A MCB. However, the information about radial circuits is written in terms of power circuits.

Initially I was concerned about lack of mechanical support as well, but realised that this isn't provided in screw terminal junction boxes anyway.

There's some rather waffly stuff on this in the Approved Doc. to Part F. Looking again, I just found a relevant comment that the fan "could be controlled" by the main light switch. Good enough. The one for the downlighters will do.

[Andy Wade]

That's why junction boxes should always be screwed to something and the cables clipped or otherwise secured near the entry points. It this case if you use adhesive-lined heatshrink for the outer sleeving you should be able to make a secure joint.

[Andy Hall]

Thanks.

Didn't realise that heatshrink was available with adhesive lining. Presumably this is like hot melt glue....

[Andy Wade]

It's readily available - RS, Farnell etc. Sticks like shit to ...

[Andy Hall]

I need to do an RS order this weekend, so it can go on that.

[Owain]

Not a problem on a radial circuit, which lighting is.

I would flush in a 2" conduit box (in fact you might already have one behind the rose) and use a screw-on cover (as used for plastic conduit systems). If you then paint over that it becomes "almost" invisible, yet remains accessible

Or you could keep the ceiling rose location and use a PIR detector to trigger the fan timer?

I'm not /quite/ sure about what you want. Are you talking about having

______ | | [] V - R O O M =====duct=====[] O - [] I - 4) I believe the Buiding Regulations specify that the fan comes on when

I suggest not using relays - use double-pole switches, one pole on each switch can switch the lights, the 2nd pole is paralled and switches the fan. This may necessitate gridswitch.

I suggest you also put in a 13A fused power spur adjacent to the WC so you can upgrade to one of those Japanese bottom-washing toilets at a later date without having to disturb the tiling.

Owain

[Owain]

Ah, I thought this had been discussed before.

how to rewire bathroom pull switch to regular light switch thread starts

's the diagram I did:

LIVE -------------- SWa Pole 1----------- LIGHT -- Neutral | |-- SWa Pole 2----- | | -- SHARED -- Neutral -- FAN | | |-- SWb Pole 2----- | LIVE -------------- SWb Pole 1 ---------- LIGHT -- Neutral

The two wires doing into SHARED FAN go to the trigger and you would also need a PermanentLive. You would also need a triple-pole isolator, of course.

Owain

[The Natural Philosopher]

Make it far bigger than you think you need, then, and use a more powerful fan, and if its hidden in the roof space, a really good quality QUIET one that won't need replacing in 6 months...;)

Not legal unless the bathroom is very big. Outside with an isolator up near the ceiling is conventional.

All lighting is spur wired.

Solder and heatshrink is allowed as is crimping. Those can be permanently boxed in and meet regs. Unless you are an avid soldere ger some crimps and a tool.

No, its fine. regs merely say you need a given airflow. How you achieve it is up to you BUT fans in long tubes are very ineffective. IIRC centrifugal fans are better than acxial.

Best of all, use a humidity controlled fan with a manual override.

[Andy Hall]

That's a thought if I could get a flush one. I want to avoid projecting pieces.

Something like that. Apart from noise reduction, I want to remove the fan from the ceiling area. I was thinking of making a compartmented area for the fan so that any dust is confined to it.

Yes of course. Simple OR function. Extra cable to the switch, but that doesn't matter.

Well actually there's just the collar for the soil pipe in the floor at the moment. I was thinking that another possibility would be to create one of those French deals where there's just a hole in the floor and a place either side to put each foot.

[John Rumm]

You can also improvise I have found.... slice slivers off a glue stick off with a sharp knife, and slide them into the heatshrink assembly before heating. The whole lot should end up nicely sealed once heated.

[Andy Hall]

Now that is creative. Excellent idea. Thanks.

[Andy Hall]

It's a ground floor cloakroom. The duct runs in the space between floor above and ceiling. The fan is OK - a Vent Axia - so no need to change. There isn't any way to get access to the duct along any of its length so hence the plan to conceal it.

It's a cloakroom - no bath or shower - so OK.

I have and can do both easily enough. I was more concerned about how to achieve a sensible second layer of insulation and a mechanically sound joint.

They are, but a lot noiser as well.

The fan is adequate so I'm not concerned about that aspect.

No shower or bath so no extra humidity...

[Owain]

Elkay 374A

What, a S*n*f*o??? ;-)

Owain

[Andy Hall]

Oh good grief no.

a look at the Japanese one. I imagine that the cistern is made by Rinnai and doubles as a combi to save space. It seems to have a flue....