Pete Verdon wrote:
John Rumm wrote:
Pete Verdon wrote:

Simplest way would be with a timber fan such as you already have -

oops make that a "timer fan" rather than a wood one!

however disconnected from the light switch. Plus an additional
external humidistat. That way you can trigger it either from the push
button (which will cause it to run for the timer duration) or from the
humidistat which will cause it to run until the RH falls below
threshold + an extra timer duration.

Yep, that's almost exactly what I have in mind, except for using a flow
switch on the shower rather than a humidity sensor. Fan would be on
while showering, and for a timer-duration thereafter.

The problem with that, is that the timer duration will probably not be
long enough to reduce the humidity completely. With a humidistat it may
need to run the fan for 40 mins or so to dry the room to normal levels.

The main problem with a push button of inappropriate rating for the
location will be what effect the ingress of moisture will have on the
switch - regardless of any voltage exposure risk.

In this case I don't think it's likely to get water on it, and in any
case its design would discourage entry even though it hasn't actually
been certified.

A momentary action pull switch may be better for the manual activation.

Probably, from a practical purpose, but I really don't like the things.
One of them (for the light) is just about acceptable since it's so
common, but multiple dangling strings (a mate's bathroom has three)
drive me nuts.

Alternatively, I could buy an IP-66 button (eg MP0031,
http://is.gd/fdko ) and wire it directly. Would this be OK? The back
of the button would be inside a substantial piece of boxing-in,
effectively a stud wall. This would have access points in it, but not
routinely openable (ie require cutting sealant).

You can get momentary action rocker switches as well that look like
ordinary electrical accessories. These may prove somewhat more
maintainable.

I'm not worried about maintainability, more whether the inside of the
boxing-in counts as part of the bathroom, since this alternative
approach would mean it contains mains equipment (and the connections to
the back of the button aren't IP-sealed). I know that the space under a
bath is non-zoned only if there is a panel whose removal requires tools
- to have my studwork treated the same way I want access to be more
difficult, not less :-)

Yup panels that need tools to get past count as if they are out of the
room. Obviously you don't want water getting under panels for all sorts
of reasons, so not getting your electrics wet is just another on the list.


--
Cheers,

John.

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