Bathroom Extractor - Wiring ?

clarkyboy · 28 May 2009

Replacing a bathroom extractor fan switched by the bathroom lighting pull cord. Am I right in assuming that the feeds will be:

1 x Neutral
2x Live (1 being the switch)

I'll naturally be having someone Part P qualified to make the connections/check them but I was wondering because standard flex has been used colour coded Live, Neutral and Earth. ie in this case the Earth is live. I'll make sure I sleeve them up correctly.

Cheers

bernardgreen · 28 May 2009

clarkyboy said:
because standard flex has been used colour coded Live, Neutral and Earth. ie in this case the Earth is live. I'll make sure I sleeve them up correctly.

Potentially lethal to have the earth conductor used as live.

Replace that cable with triple and earth.

clarkyboy · 28 May 2009

Yeah that was my feeling.

The Earth coded cable runs at 40V and then full 240V when the switch is activated so am I right in thinking that is switched live ? The Live coded cable is at constant 240v regardless of switching, so permanent live.

Is it normal for the switched live to show 40V even when switched off ?

wingcoax · 28 May 2009

Maybe some capacitance from the electronics in the timer but shouldnt really be anything there.

ban-all-sheds · 28 May 2009

bernardgreen said:
Potentially lethal to have the earth conductor used as live.

And illegal in Sussex.

clarkyboy · 28 May 2009

ban-all-sheds said:
bernardgreen said:

Potentially lethal to have the earth conductor used as live.

Click to expand...

And illegal in Sussex.

Hence the post.

clarkyboy · 28 May 2009

wingcoax said:
Maybe some capacitance from the electronics in the timer but shouldnt really be anything there.

Could you elaborate on what you mean by the timer ? Cheers

ban-all-sheds · 28 May 2009

You said the fan has both permanent and switched live - this indicates that it has a timer which keeps it running for a period after it's been switched off.

clarkyboy · 29 May 2009

ban-all-sheds said:
You said the fan has both permanent and switched live - this indicates that it has a timer which keeps it running for a period after it's been switched off.

Yes I'd assume both old and new extractor have a timer function but I'm just puzzled as to why the switched live still shows 40V with the switch off ? I am only testing the cable at the moment rather than the fan fitted.

bernardgreen · 29 May 2009

but I'm just puzzled as to why the switched live still shows 40V with the switch off

Capacitive coupling between Live wire and Switched Live wire inducing some voltage on the Switched Live. This voltage should disappear if a lamp with a filiment is fitted in the lamp holder.

Taylortwocities · 29 May 2009

Will probably also disappear if 3 core and earth cable was used with the earth (cpc) connected to earth.
This will reduce or iliminate the induced voltage.

clarkyboy · 1 Jun 2009

Cheers all. Appreciate the assistance.

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Bathroom Extractor - Wiring ?

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