Smart Socket

[RickH]

On good advice here, I am going to add a Smart socket in an outbuilding being used for external LED light string. (Fused spur)
This is protected from rain etc.

Socket I have purchased (double) is IP66, and expects a round cable and has gland to suit supply cable.
The socket will be fixed, and therefore ‘fixed wiring’
Typically I know flex cables are not used for fixed wiring, but circumstances can allow if no risk of physical damage.

Read that that BS 7671 allows flexible cables, it does stipulate that:
A flexible cable shall be used for fixed wiring only where the relevant provisions of the Regulations are met. Flexible cables used for fixed wiring shall be of the heavy duty type unless the risk of damage during installation and service, due to impact or other mechanical stresses, is low or has been minimized or protection against mechanical damage is provided.


The cable will be clipped direct to rafters, and at least 2m above floor level.
Do I need to use an NYY-J cable to meet ‘heavy duty’ requirement.

Or would I be better to use some heavy duty flexible conduit and run normal 3-core flex inside that)
Total length of run is around 3m

Rest of wiring in building is t&e all direct-clipped and visible.

 

[EFLImpudence]

A flexible cable shall be used for fixed wiring only where the relevant provisions of the Regulations are met. Flexible cables used for fixed wiring shall be of the heavy duty type unless the risk of damage during installation and service, due to impact or other mechanical stresses, is low or has been minimized or protection against mechanical damage is provided.

Do you plan on high impact or high mechanical stress damage during installation?

 

[RickH]

No neither during installation nor in use, so I can use ordinary flex? (correctly sized)

Never used a flexible cable on a mains socket before, so want to get it right, I can put the flex in flexy conduit if needed, if not needed, I will just direct clip.

 

[EFLImpudence]

Yes, just treat it the same as T&E.

 

[RickH]

Thanks

Related Q .... this will get its supply from a Wylex enclosure;

Is it OK to run the cable direct to a 6A MCB, providing a dedicated radial cct for this socket, rather than run MCB to a fused spur unit, and then connect new socket to that.
Current limit provided by MCB safety is covered, and is simpler.

The supply to the Wylex enclosure comes from 30mA RCD protected 32A radial circuit.

 

[EFLImpudence]

Is it OK to run the cable direct to a 6A MCB, providing a dedicated radial cct for this socket, rather than run MCB to a fused spur unit, and then connect new socket to that.

Yes, there is no point having an Fused Connector Unit on a 6A circuit.

Current limit provided by MCB safety is covered, and is simpler.

Exactly - and of course from the plug fuse(s)

The supply to the Wylex enclosure comes from 30mA RCD protected 32A radial circuit.

Ok.

You are allowed one (double) socket on a spur(the cable) without the MCB because the plug fuses will do the same job.

 

[EFLImpudence]

You are allowed one (double) socket on a spur(the cable) without the MCB because the plug fuses will do the same job.

That is if the spur cable is 2.5mm² and can handle the current allowed by 2 x 13A plug fuses.

If you want to use smaller cable then the 6A MCB will be the way to go.

 

[EFLImpudence]

Too many options really - what is the rating of the smart socket? Usual 13A?

 

[RickH]

Smart socket is 13A ... I only need it to handle <2A, as the 2 LED strings combined are 40W, even allowing for some conversion loss, still very low current draw.

Hence I thought MCB at 6A is more than adequate .... the strings themselves will be dasiy chained to a single 3A fused plug.

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Using MCB option limits current, and avoids the need for Fused Spur box.

Reason for the WYLEX enclosure is the capacity for a 2nd MCB if I needed to add another light in the future, I'll use 2.5mm t&e to the box.

A picture is supposed to be worth a 1000 words so the attached may help

 

[EFLImpudence]

Smart socket is 13A ... I only need it to handle <2A, as the 2 LED strings combined are 40W, even allowing for some conversion loss, still very low current draw.

Ok. Fair enough.

Hence I thought MCB at 6A is more than adequate .... the strings themselves will be dasiy chained to a single 3A fused plug.

Yes, that would be adequate for what you want.

Using MCB option limits current, and avoids the need for Fused Spur box.

Well, yes, it does but what is the difference?

Reason for the WYLEX enclosure is the capacity for a 2nd MCB if I needed to add another light in the future, I'll use 2.5mm t&e to the box.

Ok. If you want two switches, As you said 6A is plenty for many lights.

A picture is supposed to be worth a 1000 words so the attached may help

Ok.

 

[RickH]

Well, yes, it does but what is the difference?

only that Wylex enclosure is there, so easy to add MCB, saves hacking to buy a Fused Spur, that was only reason.

 

[EFLImpudence]

Fair enough.

 

[winston1]

Reason for the WYLEX enclosure is the capacity for a 2nd MCB if I needed to add another light in the future, I'll use 2.5mm t&e to the box.


View attachment 280959

That would then be 2 spurs off a spur which is not allowed.

 

[EFLImpudence]

That would then be 2 spurs off a spur which is not allowed.

That is not true.

With 2.5mm² cable: if they are limited to 13A by an FCU (it being 13A merely because that is the maximum rating of fuse that will fit in an FCU - 25A would do if there were one).

Do you not think two 6A MCBs (or indeed two 13A MCBs) would have the same effect?

OR of course -

The use of larger cable.

 

[ericmark]

There are many ways to do what you want, I have used smart relays for one of my lights, the consideration is what is the default.

Smart bulb default normally on, smart socket default normally off, the relay seems to be off, not had a power cut to test. I have returned home to find bedroom lights in my flat on after a power cut, at 15 watt not really a problem.