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Smart relays on ring mains

vantech

Hi, 

I have installed plenty of these devices, as well as their dimmer range. 

https://shelly.cloud/products/shelly-1pm-smart-home-automation-relay/

What I am seeing however, is a number of people within online forums, installing these smart relays on ring mains. What they are doing is spurring from a ring, in 2.5mm and then switching this spur with the relay (without any form of fusing down, via means of an FCU). 

I do not believe this is compliant, for the following reason: 

  • The relay is rated at 16A, and although it has overload protection, this is electronic and if the contact welds, the overload would not be broken by the relay itself.

If installed after a 13A fused connection unit, the device is not only protected by a 13A fuse (less than the contact rating) it is also then seen as some sort of appliance. 

Is there anything else to add to this? 

Would anyone here actually install these relays in-line with a ring main and if so, why/how does this comply with BS7671? 

A few people have stated that the likes of Click Smart have a similar setup in a double socket: 

https://click-smart.com/products/mode-smart-sockets

However these are covered by a product standard and not BS7671, so the application is very different. 

Thoughts? 

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  • 0

    It would certainly be cleaner with a 13A fuse on the supply side - not least because you can make it safe without killing power to the whole ring by taking that fuse out.

    The correct thing to do of course is to Email the makers, but it may be worth explaining what a ring final actually is - the company has offices in Bulgaria, Germany and the US, none of which expect sockets to be fed from 32A B type breakers.

    How it fails and if it is actually dangerous is unclear - it certainly should never be relied on as the means of safe isolation to work on something, and I can imagine the relay may either weld up as a dead short or blow open after an overload, so it can only be used for loads where that would be a nuisance but not a disaster.

    I'm not seeing CE marks in the photos, but they may be on the paperwork, or it may be  up to the end user to test and certify - which would be out of scope for most electricians.

    If the odd home enthusiast wants to try it on known low power loads, the real risk is low. I'd be surprised if any responsible sparks would be keen to adopt the responsibility however.

    Mike

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  • 0

    It would certainly be cleaner with a 13A fuse on the supply side - not least because you can make it safe without killing power to the whole ring by taking that fuse out.

    The correct thing to do of course is to Email the makers, but it may be worth explaining what a ring final actually is - the company has offices in Bulgaria, Germany and the US, none of which expect sockets to be fed from 32A B type breakers.

    How it fails and if it is actually dangerous is unclear - it certainly should never be relied on as the means of safe isolation to work on something, and I can imagine the relay may either weld up as a dead short or blow open after an overload, so it can only be used for loads where that would be a nuisance but not a disaster.

    I'm not seeing CE marks in the photos, but they may be on the paperwork, or it may be  up to the end user to test and certify - which would be out of scope for most electricians.

    If the odd home enthusiast wants to try it on known low power loads, the real risk is low. I'd be surprised if any responsible sparks would be keen to adopt the responsibility however.

    Mike

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