FCU for spur to outside socket

Aug 13, 2019 Last reply: 6 years ago 12 Replies
S

I have a 4mm radial (via 32A RCBO) which will have a a 2.5mm spur off to an IP rated exterior socket on the outside wall of the house. I intended to use a 13A fused double pole FCU with the spur off, thereby having isolation to outside, and a fuse on the spur for good measure. These are available and I suppose have fuse on live but double pole isolation.



But, the switch needs to look good and match others nearby which are flat plate screwless designs (BG range from Toolstation). And in that design I can only find single pole FCUs with no isolation to outside (neutral always connected).



So how important is double pole isolation to the exterior socket ?



Thanks, Simon.


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J

To allow you to isolate a neutral to earth fault on the load side of the FCU which is causing your RCBO to trip?

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S

This *says* double pole

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Owain

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S

Well I found one without a neon (which is fine) in the B&Q "Colours" range of all things. The photo on the website has "BG lic no 1015", and you can see on the rear photo that it is definitely DP. So ordered it Click and Collect.

I don't really like relying on things that are not widely available because you can get stuck down the line. But anyway ...

Simon.

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S

Thanks. I don't need the flex outlet, but the way it is done in the picture looks very neat if left unused.

Simon.

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D

Must admit I thought all FCU changed to DP at the same time as 13 amp sockets.

Dunno your BG range - do they have a grid system which matches? 20 amp DP switch plus fuse unit?

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R

The BG Nexus FBS50 has double pole isolation according to the data sheet

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S

Can anyone confirm that FCUs are generally DP even if they do not say so ?

If that is the case I have been wasting energy. I'll remember next time to look for the official data sheets, which are not always available from retailers website.

Simon.

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D

I'd assumed they were. Because of RCDs. No real point in having an isolator that doesn't isolate a neutral/earth fault. Making a DP socket rather overkill - since you could just unplug the faulty appliance.

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P

I recently used a 30+-yo MK SFCU and that's double pole. I've used quite a lot at work and home and never seen a single pole one.

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R

I think the definitive answer is in the regs. In the 17th, Table 53.2

- Guidance on the selection of protective, isolation and switching devices - lists devices and the functions they can perform. A switched fused connection unit to BS 1363-4 has a "Yes" in all 3 columns so can function for Isolation, Emergency Switching and Functional switching.

In short, yes if to BS1363-4.

I learnt to do that the hard way too ;)

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A

I knew it would have, and so did you:-)

Actually there is no reason why it needs to be a FCU. A 20A double pole switch would be allowed.

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