Placing the FCU before the ceiling rose would achieve full isolation but then the fan couldn't be isolated independantly and working on the fan without light.
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Double Pole isolator switch for Bathroom Light Pull & Extractor Fan?
- Thread starter Roy22
- Start date
If this is correct, why do I find a (rear left) live wire in the isolator when the FCU is switched off? Surely the desired complete isolation has failed?
As I implied, having just an FCU has obviously got to be cheaper than having an FCU PLUS a 3-pole isolator (the latter seemingly being what most manufacturers 'require'), but that has to be partially offset by the fact that a DP light switch would cost a fair bit more than a bog-standard SP one.
Also "rear left" is not a helpful electrical specification.
Quite so - that's why the approach we're discussing is arguably 'better'. The only (crazy) alternatives would be to have 2 FCUs!
I have no idea what you mean by the 'rear left wire'
I'm also not sure what you mean y 'the isolator'. I was referring to EFLI's diagram, in which the effective 'isolator' is the FCU, and that would obviously still have a live feed (on its 'supply side) even when it was 'witched off'. What 'isolator are ou talking about?
Rear left means looking at the picture I posted, the furthest of the two red wires coming from the left. By isolator I mean the pull switch, as stated it is a 16A isolator.
As the diagram EFLI has posted illustrates, no matter which of those you are talking about, one of the red wires will remain live even when the isolator is switch is 'off' [that's how switches/isolators work - they cannot 'magic away' the incoming live electricity - they merely disconnect it from the outgoing terminals]
Yes but the isolator/pull-switch is supplied by the nearby FCU, and when that is switched off, the isolator/pull-switch still has this single live wire. This is what baffles me.
What don't you understand about the diagram in EFLI's post #24? Per his big red arrows, both the "DP Switch" and the "DP Switched FCU" have a feed (from the ceiling rose) which is always live, regardless of whether either or both of them are switched on or off.
So - you don't understand the diagram nor how the system works.
The pull switch is not being used as an isolator, merely a functional switch, but it would still have a permanent live even if it were an isolator.
Yes I do understand the diagram, thanks. What I don't understand is what this achieves. As you say, the pull switch serves merely as two single pole switches for the two loads, light & fan. No more isolation that a wall switch does a for light bulb. And this arrangement carries the great gift of a permanent live in the pull isolator switch even after disconnection at the FCU, for the unwary. If the FCU had instead fed a simple, single pole switch, the output could have then run to the lights and the fan's switched live input.
A permanent live for the fan could then have been run more safely/obviously from the input to that simple switch. The fan supply (permanent & switched lives) would have benefited from the FCU's 3A fuse along with the fact this is in turn powered from the light circuit, with 6A MCB back at the fuse box.
And when I go to Screwfix and major electrical factors, I find plenty of single pole switches to choose from, whilst these 16A isolator pull switches are either not sold or not in stock. As if few do this. Yes, I found one eventually. Please enlighten me what the benefits of this circuit are.
A permanent live for the fan could then have been run more safely/obviously from the input to that simple switch. The fan supply (permanent & switched lives) would have benefited from the FCU's 3A fuse along with the fact this is in turn powered from the light circuit, with 6A MCB back at the fuse box.
And when I go to Screwfix and major electrical factors, I find plenty of single pole switches to choose from, whilst these 16A isolator pull switches are either not sold or not in stock. As if few do this. Yes, I found one eventually. Please enlighten me what the benefits of this circuit are.
It allows isolation of the three fan conductors with a two-pole switch.
That might not be the most important thing in the universe but that's it.
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