FCU and socket question

tireetim · 21 Apr 2010

Hi, I know the norm for kitchen appliances (Fridge / Dishwasher etc.) is to run a spur with a FCU switch above the worktop and a socket without a switch near to the appliance. I have two questions :

1. Can the fused switch and socket be combined into one? If so, Is a standard swiched socked acceptable?
2. Alternatively, can the appliances be hard wired into the FCU instead of using a plug / socket?

Thanks.
Tim.

PrenticeBoyofDerry · 21 Apr 2010

The reason why a switched FCU is used is so the appliance can be isolated, before removal from under worktop.
So can't see any logic in question one. Even if you could get such an accessory.
Question two, it could but removing the plug top from the appliance would make any warrnties invalid, and also removal of the appliance would not be straight forward.

tireetim · 21 Apr 2010

Yes but I thought the FCU was also for protection (hence the Fuse and not just a switch). So if it's just for isolation purposes can you just use a switch (or a switched socket). In other words, is the fuse necessary?

Steve · 21 Apr 2010

Some sparks use a 20 amp switch above the worktop, relying solely on the 13A fuse in the plugtop below. Its a better design because theres only one fuse.

Spark123 · 21 Apr 2010

Daft as it sounds I don't think a 20A DP switch can be installed on a RFC as it isn't to the required standard.
Fused spurs are to BS1363 which are allowed on a RFC.
If the appliance is fixed then you should have an accessable point of isolation, however if they are free standing you don't need to have the switch above the counter albeit it is imo a good idea anyway.

wingcoax · 21 Apr 2010

Yes, BUT! what if the appliance has become live? without blowing the fuse(can happen) or is on fire? how do you move said appliance to switch off/unplug?

electronicsuk · 21 Apr 2010

wingcoax said:
Yes, BUT! what if the appliance has become live? without blowing the fuse(can happen) or is on fire? how do you move said appliance to switch off/unplug?

For the vast majority of Joe Public, I would assume they would run straight to the consumer unit and switch off the main isolator. I suppose it depends whether the local isolation is supposed to be for functional/maintenance or emergency purposes.

wingcoax · 21 Apr 2010

Also depends on where the main isolator is, how would most people react? i think they would go for a switch if there was one nearby.

LoveRocket · 21 Apr 2010

Spark123 said:
Daft as it sounds I don't think a 20A DP switch can be installed on a RFC as it isn't to the required standard.
Fused spurs are to BS1363 which are allowed on a RFC.
If the appliance is fixed then you should have an accessable point of isolation, however if they are free standing you don't need to have the switch above the counter albeit it is imo a good idea anyway.

Heh heh, that's a great old (or relatively new) chestnut, and one I happen to agree with. Can you connect a 20A accessory on a 32A RFC? None of the accessory manufactures would say 'yes' (see long thread on the IET forum). There's a reason why you get lightswitches rated at 6A or 10A.

"Yeah yeah,, but if it's only feeding a single socket then there will be a fuse in the plugtop"
"Yeah but you're allowed a spur from a 32A RFC on cable that's not rated for 32A..."
"But but but loads of sparks do it!"

PS. There's no requirement whatsoever for non-integrated kitchen appliances to have an isolator above the worktop. The NICEIC might like it, but they don't make the rules.

ban-all-sheds · 21 Apr 2010

LoveRocket said:
Heh heh, that's a great old (or relatively new) chestnut, and one I happen to agree with. Can you connect a 20A accessory on a 32A RFC?

Of course you can. BS 1363 sockets only have to be able to cope with 20A passing along the cable which they are on, and standard unfused twin outlets only have to be able to cope with 20A being drawn from them.

Go figure.

PS. There's no requirement whatsoever for non-integrated kitchen appliances to have an isolator above the worktop.

Or integrated ones.

davelx · 22 Apr 2010

PrenticeBoyofDerry said:
Question two, it could but removing the plug top from the appliance would make any warrnties invalid,

In the vast majority of cases it doesn't, really! In fact they generally provide instructions on how to fit a different plug if the moulded supplied one is not suitable.

LoveRocket · 22 Apr 2010

ban-all-sheds said:
Of course you can. BS 1363 sockets only have to be able to cope with 20A passing along the cable which they are on, and standard unfused twin outlets only have to be able to cope with 20A being drawn from them.

Go figure.

I agree that it's a bizarre standard, but why would none of the manufacturers state that their 20A DP switches could be fitted on a 32A RFC.

What about a 32A radial, would you consider it acceptable to use a 20A switch on such a circuit if there was a plugtop fuse downstream?

ban-all-sheds · 22 Apr 2010

LoveRocket said:
I agree that it's a bizarre standard, but why would none of the manufacturers state that their 20A DP switches could be fitted on a 32A RFC.

Maybe they fear that the switches might be used in a way that has a load of more than 20A going through the contacts, rather than just in and out of the terminals?

Ditto 32A radials, of course.

I wonder why, if they don't believe they can be used on >20A circuits they make them with terminals which can take 2 x 6mm² cables?

What about a 32A radial, would you consider it acceptable to use a 20A switch on such a circuit if there was a plugtop fuse downstream?

Define "acceptable"....

IMO it would be perfectly safe, as the load on the switch is limited to 13A.

Would it contravene the regulations because it's not what the manufacturers say you can do? I'm not so sure that the manufacturers do say that you can't use them that way. Look at the technical specs for MK Logic, for example:

Current rating:
Connection units – 13 amp
DP switches – 20 amp
Flex outlets – 20 amp

If the 20A in the switch spec means that you can't put it on a 32A circuit to switch a load of ≤ 20A, what does the 13A in the FCU spec mean?

If someone did not explicitly ask the manufacturer about putting a switch on a 32A circuit, and instead just read their specifications, what interpretation would he place on a specification like that, reading it with reasonable skill and care?

As I have often said, if there are two ways to interpret something, and one of them introduces illogical conclusions and inconsistencies where the other does not then you ought to seriously consider if that one is wrong.

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FCU and socket question

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