Using a 13 amp socket on a 5 amp circuit

[#1]

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@Mustrum wrote:

Whilst not yet as bad as the USA for regs, the ones we do have demand that any gas or electrical work is signed of by suitably qualified "professionals".

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Can you be more specific? If you're referring to the notification requirement of Part P then that only applies to new circuits, replacement consumer units and any electrical work in a 'special' location (a room containing a bath/shower, swimming pool or sauna heater). There is no need to have the addition of a socket to an existing circuit 'signed off', but it is required to be compliant to the regs.

With regards to the regs, and BS7671 in particular, there is no black-and-white rule either way regarding adding a 13A socket to a lighting circuit. It does go near the subject though, for example it says that a 'lighting' circuit can have a BS1363-compliant socket (which a reputable 13A socket would be) attached to it although elsewhere it states that a 'power' circuit must use a minimum conductor size of 1.5mm²and so if plugging a non-light into a lighting circuit does that therefore make it a power circuit in which case the commonplace 1.0mm² 'lighting' wiring might therefore be deemed inadequate? The regs remain silent on that point.

As always the regs are often open to a certain amount of interpretation - intentionally - because often there is no one size fits all rule. Hence, deviation from the regs is not automatically deemed a contravention. There is room for pragmatic judgement, and in the case of 13A sockets on lighting circuits this is frequently exercised - there are thousands of houses across the country with TV distribution and masthead amplifiers plugged into 13A sockets on lighting circuits because often that is the only power source available in lofts. Likewise with undercupboard lighting using plug-in lighting but where wall switch control is still desired. Professional electricians will usually mark up the socket to advise against plugging anything else in and some (along with perfectionist amateur DIYers, usually) will also add in an 3A FCU for belt and braces protection against such a situation occurring and in doing so helps uphold the regulatory requirement to minimise the risk of long-term small-overload (i.e. non fault) situations occuring.

An alternative, albeit bulky, approach would be to stick with the round pin 5A socket and make up a 5A plug to 13A socket adapter lead through which to power the new radio. This requires no modification to the fixed wiring whatsoever, although the risk of plugging something else in would persist for as long as the adapter lead remains in existence.

Personally, I'd go with a 3A FCU and marked-up 13A socket. I'd possibly ditch the 3A FCU if there were practical or significant aesthetic issues and not lose any sleep whatsoever.

[#2]

Thanks for all the contributions and sorry it has "sparked" such indignation ! 

I prefer to go with common sense.  Life's too short for Pythonesque heel-clicking.  My old radio has been plugged into the lighting circuit for thirty years and it will continue to be but with a 13 amp socket and 3 amp inline fuse.  I can easily secure the transformer to ensure it cannot be removed.

If I were to buy an inline transformer, I would run the risk of invalidating the guarantee on the radio, although I am grateful for the suggestion. 

A 13 amp fuse in the plug, tamper-proofing the transformer, a 3 amp inline fuse in the wall box and an RCD terminating the lighting circuit is enough belt and braces for me, especially as there are only two of us in the house and no-one is even likely to know that the socket is there, so little risk of anyone tampering with it.

I live in the real World, and believe it is always best not to be too proud to ask, but to seek information and then to weigh up the answers on the back of knowledge and practicality.  The trouble with feigned indignation is that it discourages people from seeking advice in the first place !  Some of you may care to bear that in mind in future.

Once again, I am most grateful for the sensible input.

[#3 · Accepted solution]

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@MJN wrote:

With regards to the regs, and BS7671 in particular, there is no black-and-white rule either way regarding adding a 13A socket to a lighting circuit. It does go near the subject though, for example it says that a 'lighting' circuit can have a BS1363-compliant socket (which a reputable 13A socket would be) attached to it although elsewhere it states that a 'power' circuit must use a minimum conductor size of 1.5mm²and so if plugging a non-light into a lighting circuit does that therefore make it a power circuit in which case the commonplace 1.0mm² 'lighting' wiring might therefore be deemed inadequate? The regs remain silent on that point.

Personally, I'd go with a 3A FCU and marked-up 13A socket. I'd possibly ditch the 3A FCU if there were practical or significant aesthetic issues and not lose any sleep whatsoever

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Thank you for an opinion based on facts.

[#4]

As a closing comment, following MJN's sensible suggestion, I have decided to keep the original 5 amp socket to which I will plug in a short extension lead, at the end of which will be a 13 amp socket and enclosure with an inline 3 amp fuse, into which the transformer will be plugged; the power cable will then exit the void and run back up the cupboard to the new radio.

I have discovered that the floor cupboard fixed to the wall in question (a standard kitchen cupboard, but to avoid Mustrum raising another hare, I hasten to add this is NOT in a kitchen of any sort) of course has the usual kickboard hiding the adjustable plastic feet.  By removing the kickboard, I will hide the transformer in the void underneath out of sight, strapped firmly to the 13 amp socket to prevent the socket from being used for anything else, and then simply replace the kickboard.

This solution ticks all the boxes.

So thanks to everyone for an entertaining but nevertheless instructive discussion.  It has been most helpful.

Moderators Note: Needlessly insulting paragraph removed. 

[#5]

It still doesn't stop anyone unplugging your radio and running an electric fire on the lighting circuit.

Do it properly and use a 13A circuit!

Your lighting socket should have a blanking plate installed.

[#6]

Not sure if I am following this thread correctly.... but am assuming you have a "wall wart" psu for the new radio with a 13amp type square pin plug moulded to it... and you want to be able to "convert" that to a 5amp round pin  to use the existing location of power from a lighting circuit,by making up some sort of extension lead 

so... instead of what has been suggested... ( which.. as Mustrum and others have pointed out.. "could" prove to be dangerous to someone who does not know, or understand, what you have done at that particular point ..) .

would one of these be a viable option...

https://www.ebay.co.uk/itm/112493170886?hash=item1a311d90c6:g:F2EAAOSwy79ZdSe6

[#7]

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@shutter wrote:

would one of these be a viable option...

https://www.ebay.co.uk/itm/112493170886?hash=item1a311d90c6:g:F2EAAOSwy79ZdSe6

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No, as 5A sockets are 3-pin... (and the pin diameters and separation are different just in case someone suggests shoving it in anyway!) 

[#8]

@MJN  Yeah.. I know 5 amp sockets have three pins...  but only two carry power... ( as in the 3 pin wall wart ) . the third pin is (probably) not even wired up on the wall wart. but just there to facilitate the plug part being able to access shuttered 13 amp wall sockets. 

[#9]

@shutter , @VileReynard 

I am quite aware that this practice is undesirable but from a quick check, 1sq mm cable, as used in lighting circuits, is rated to carry 11A continuously in a 30 degree ambient rempersture. A standard 6A B curve MCB as used on lighting circuits will trip within 4 seconds at 9A worst case. The higher the current the faster it will trip.

So I repeat, Where is the risk with modern wiring protected with a MCB? I agree if it’s an old building with wired fuses then that’s potentially dangerous if an idiot plugs in a high power consumption device.

[#10]

Searches would suggest that 13A to 5A round pin adaptors don't exist, which is reassuring.  😉

[#11]

The MCB is the single point of failure.

I'm betting you never test it.

[#12]

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@VileReynard wrote:

The MCB is the single point of failure.

I'm betting you never test it.

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How do you do that? 

[#13]

A) Check that the MCB actually includes your power point by switching it off.

B) Plug a high current device in and hope the lights go out quickly...

[#14]

High current testing is not an accepted method of in-circuit testing in domestic environments given the potential risks. MCBs are assumed to be working within spec unless symptoms exists to suggest otherwise (eg below-rating trips, mechanical issues etc). You're really just limited to checking they manually turn on and off. (Ref: IET Guidance Note 3)

[#15]

So why bother with a consumer unit with RCD's and MCB's supplying internal sockets?