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#137152 - 06/02/03 03:07 PM isolation arrangements
james S Offline
Member
Registered: 05/13/03
Posts: 102
Loc: West England
1. when installing a ceiling fan is it a requirement to fuse down the feed of the lighting circuit if not is double pole isolation required?

--------------------------------

2. when installing extractor fans ( the type that run on after the light has been switched off) in toilets/bathrooms, is it a requirement to isolate all three live conductors L , switch L AND NEUTRAL . and does this also need to be fused down from the lighting circuit?

ps i do have a copy of BS 7671 and on site guide, but sometimes find it so hard to come to any kind of conclusion as to what are the correct requirements .


[This message has been edited by james S (edited 06-02-2003).]
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#137153 - 06/03/03 04:00 PM Re: isolation arrangements
David UK Offline
Member
Registered: 10/03/02
Posts: 134
Loc: Inverness, Scotland
Hi James,
1) I can see no requirement to install any further fuses if your protection is a 5A fuse or 6A mcb. These OCPD's should provide adequate short circuit protection for the fan & wiring. In other countries these fans are installed on 10/16A circuits without further fusing down.
I am not certain about DP switching being a requirement if you do not have a timer circuit.

2) Extract fans with run-on timer are required to have 3 pole fan isolation switches installed for maintenance purposes.
As regards fusing down, if 5/6A mcb, I would not say so.
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#137154 - 06/04/03 02:47 PM Re: isolation arrangements
lyledunn Offline
Member
Registered: 06/30/02
Posts: 159
Loc: N.Ireland
David,
Please detail reg nos which requires 3pole switching.
I see no requirement for double pole or 3-pole isolation in such circumstances.
_________________________
regards

lyle dunn
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#137155 - 06/05/03 12:44 PM Re: isolation arrangements
james S Offline
Member
Registered: 05/13/03
Posts: 102
Loc: West England
The reason i ask is because of the specifications on the manufactures instructions, if i find them i will post them on.
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#137156 - 06/06/03 01:20 PM Re: isolation arrangements
pauluk Offline
Member
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
One practical advantage of a 3-pole isolator is where the system uses TT earthing. Opening the permanent-live and switched-live feeds makes it safe to work on the fan, but if during maintenance you accidentally short neutral to earth you can still trip out the main RCD.

As for the fusing, I find it somewhat amusing that the instructions for many devices here make a big point about how a "3-amp fuse MUST be fitted" or whatever, yet the exact same device is considered perfectly acceptable on the Continent wired on a 16A circuit with no such warnings.
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#137157 - 06/06/03 03:47 PM Re: isolation arrangements
james S Offline
Member
Registered: 05/13/03
Posts: 102
Loc: West England
I agree i don't think there is any problem with the fusing arrangement off a lighting circuit, i think the manufactures are just trying to cover themselves.thinking about it the only way to fuse the timer type fan, is to install two fuse spares which is a pain in th arse and will look stupid!


ps thanks all for your views
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#137158 - 06/08/03 10:38 AM Re: isolation arrangements
PaulCornwall Offline
Member
Registered: 06/02/03
Posts: 112
Loc: England
i was always taught that the purpose of the fuse was to protect the cable..
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#137159 - 06/09/03 02:41 PM Re: isolation arrangements
pauluk Offline
Member
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Quote:
thinking about it the only way to fuse the timer type fan, is to install two fuse spares

Not quite. You could use a single fuse which feeds both the fan and its associated light.
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#137160 - 06/12/03 11:10 AM Re: isolation arrangements
james S Offline
Member
Registered: 05/13/03
Posts: 102
Loc: West England
I SEE WHAT YOUR SAYING WHICH IS POSSIBLE IF NEW INSTALLATION BUT I WAS THINKING MORE ALONG THE LINES OF INSTALLING ADDITIONAL FANS TO EXSISTING LIGHTING CIRCUITS.

TAKE YOUR POINT THOUGH
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