13A Socket outlets - SP or DP?

[harryagain]

I think we are just in a transition period. Before long they'll all be double pole switched.

[Kevin]

I see that many suppliers now offer both SP and DP versions of switched sockets, with DP up to 50% dearer for a given make.

What governs which version one should use?

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Kevin

[Caecilius]

I'd prefer DP, as it means the appliance can't trip the RCD when the switch is off.

With SP, an N to E short in the appliance could still cause a trip even if the socket is switched off.

[Tim Watts]

Use what fits the box - unless you are putting in a new backbox, then I prefer doubles. But it depends on your expected use.

[Tim Watts]

Oh sorry - I read that as Single Gang, Double Gang.

Makes not much difference most of the time...

[spuorgelgoog]

You can't use a switched one of any variety for supplying a boiler.

Owain

[charles]

I don't, having made my own decision 26 years ago. Is it now in the regs?

[Mark Carver]

What's the logic behind that directive ?

[charles]

my logic was that removing power to the system, which includes the pump, could result in overheating of the boiler and a consequent shut down, so that when power was restored the boiler wouldn't restart. This could, if I wasn't at home, result in expensive call out charges.

[fred]

I'd guess at safety concerns.

The heating system should be isolated for maintenance and that means double pole isolation. Since switched sockets can be either single or double pole switched then there is a risk that using the switch alone could result in a incomplete isolation.

If an unswitched socket is used then there is no ambiguity, the system is isolated by removing the plug which will always result in double pole isolation. If a switched FCU (Fused Connection Unit) is used instead, these are required to be double pole switched so full isolation is achieved. It would be common to remove the fuse too if working on the system.

I'm sure Adam will pull me up at some point if I've misread the reasons for the rules.

[Mark Carver]

Does you boiler carry on heating with the power removed ? It's no worse (or better) than suffering a power cut surely ?

I can understand the need to isolate fully for maintaince etc. Mine is fed by a DP FCU.

[Roger Mills]

You'd better make sure that you never have a power cut then!

[Tim Watts]

How is a switch different to pulling the plug?

I've also heard the "the switch might not be DP" but I would have though if you really wanted to isolate the system you'd pull the plug out...

[Tim Watts]

In fact that makes no sense at all - I've seen boilers with switched FCUs feeding them.

[Tim Watts]

Well - it is undesirable but power cuts are rare. I would always turn the boiler off at it's own control first, wait for the pump to go quiet then cut external power.

[Kevin]

If a low water content boiler, set at its maximum flow temperature, is running balls-out when the power goes off, the over-temperature trip might pop: but anyone who is competent to arrange an expensive call-out could also be trained to press the tit to reset it.

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Kevin

[Bob Eager]

Indeed. I have one, and I fitted it.

[charles]

For my boiler you need to take the cover off - using a screwdriver - to reset the trip. That is slightly more complex than picking up the phone. At least its to some people.

[A.Lee]

Care to explain why you think that?

[John Rumm]

There is no regulatory requirement that I am aware of, although it makes sense not to use switched sockets for critical appliances (boiler, freezer etc) where one would not like them to be accidentally switched off.