A customer had a rant at me, because I installed double pole switches upfront of the Smart switches he had bought for his immersion heaters, I explained they were there for safety to allow plumbers and electricians to work on his hot water tank and immersion heaters safely and refused to remove them, despite him saying they were not required and he didn’t want them.

Bear in mind all of these switches are out of sight in his airing cupboard and I had to run two supplies through off-peak smart switches to get it to work, making it clear to anyone working on it in future what I had done.

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

If its controlling one double socket spured off the ring main then its no different to having a double pole switch in its place. A double socket is only rated at 13A culminative these days anyway so the relay can take that 

It rather depends what upstream protection the relay module is intended to be used with. You have to consider not just normal operation (if that was true we could omit all fuses and breakers back to the substation - I cannot imagine many folk recommending that) but also what happens during any credible failure modes, and if the relay unit is part of the fixed wiring, then that is faults both in the electronics pod of the relay, and up and downstream of it.

I do not think it is clear cut - it may be internally designed to fail safe, but given the costs is less than £20, probably not.

Maybe I'll ask the makers.

M.

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.

The regs get a bit messy with this sort of thing, as there are a lot of different characteristics to consider. Roughly speaking overload and fault current protection may be treated separately, with with the possibility of overload protection being downstream (or even implicit in the nature of the load), so often it's the fault current characteristics that need to be considered - which are often rather different to the simple long duration current rating of an item. It's the kind of consideration that lets us use what's basically 20A cable for an unfused spur from a 32A ring circuit.

In the old days we'd sort of consider a 16A accessory as being roughly equivalent to a 16A conductor and calculate on that basis but that always was a bit of a kludge especially where the device is capable of making onto a fault or attempting to break a fault current - these days there's an entire section (536) demanding we consider all sorts of characteristics, but I think in most cases it boils down to 'ask the manufacturer' - either for stacks of data or just for their requirements for upstream protective devices for fault protection.

   - Andy.

I recently ordered a Shelley Pro 1 https://shelly.cloud/knowledge-base/devices/shelly-pro-1/

for a museum installation and to my dismay discovered that the primary power with this new version module was mains in only not 12V dc earlier version.  I understand from the vendor that this product has UL and FCC  AU/NZ CE approvals. However, I would seriously question the safety of a product that is din rail mounted with a gap of barely 2mm between the metal conductors between the screw terminals. I would leave an air gap of at least 5mm for L-N separation.

Note that I have informed the vendor of my opinion and will definitely not use this module in our current project.

Thoughts, please?

 

can you post a pic of the offending terminals on the new model ? It is non too clear from the weblink, and the risks for clearance (a free air gap) and creepage (the distance electricity would have to flow along the  wiggles of a surface if it was say damp or contaminated) are quite fifferent and depend on the details of the design.

Oddly when this thread was first opened I did contact the suppliers technical folk, who were kind enough to reply by email from Bulgaria, but the response was not exactly unequivocal and as feared they were indeed a bit shaky on UK wiring practice.
Mike.

Hi, 

I think there are many products on the market that have L&N side by side. Look at LED drivers for example.

Can you elaborate more on your meaning? 

So it's the terminals on the bottom of the device. 5mm

pitch. The lower ones are obscured but on the same pitch as the higher level, screw terminal is shown. I've since returned the unit and have not taken any images other than a side profile, unfortunately.   Yes a company based in Sofia

The product compiles with required standards and carries a CE mark. I am also pretty sure Shelly use external labs for the certification of products as many of them are also UL listed for the states. 

Where does this 5mm distance come from?