Shelly 1 - Immersion control
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01-12-2022 12:26pm#1
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I've plenty of experience installing immersion heaters in the dairy industry and have first hand experience of seeing all kinds of switches failing most rated well over 16A.
Not sure how these relays get the rating they do but very much doubt they are actually rated to carry a constant 16A or even 12A for hours at a time like an immersion heater requires.
I'm a big fan of Shelly devices but having disassembled them I'm totally unconvinced of their safety for this application even the screw terminal are too light duty for the both the load and the physical cable size.
Personally I'd use the Shelly and a decent contactor, it won't be that much more expensive or complicated to install but could well save you from a fire.
Just look at the size of the Shelly and consider the size of the terminals in your standard switches that failed, which were probably rated at least 20A. Most of these fail due to cables being too loose or contacts not closing tightly enough.
Post edited by emaherx on2 -
The above is right, especially regarding the terminal sizes etc. Funnily the relay is probably fine. The reason I say that is because I was researching this exact thing a while ago when I was looking up an immersion module I had in an old apartment - fairly conventional. I found a teardown on youtube and the relays used for the boost are the same manufacturer as that Shelly relay. https://www.youtube.com/watch?v=JJ6Chd9GjpY
Granted the terminals, spacing and other components are probably all better and not packed in like the shelly.
A DIN contactor controlled by the shelly on the consumer unit would probably be the best bet, although that would make the physical switch redundant. I second the above and would not put in the Shelly alone!
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There are loads of suitable contactors, I don't have any particular model to recommend.
But I'd look for at least a 20AMP 2 Pole NO contactor with 230V coil voltage. You could go for even higher Amps for longer life but there will be a louder clunk noise from switching.
Wiring is simple, wire the contactor in series with the switch, the coil terminals marked A1 and A2 are connected to the load of the shelly.
Another thing to bare in mind if Shelly and contactor coil are being powered from same circuit as the Immersion then they should be protected by a separate circuit breaker or fuse as your immersion is likely protected by a 20A breaker and these are not rated for 20A, a fault condition in the Shellys own circuit would likely cause a fire before tripping a 20A CB.
For neatest installation a small enclosure with din rail and space for a Din mounted Shelly, the contactor and a 10Amp CB would be best.
DO NOT remove the existing Immersion Switch, it should be left in place for isolation.
Also, be careful undertightening terminals leads to early failure due to overheating and over tightening will damage them leading to the same situation. If in doubt get your electrician back.
A quick Google brings up this 25A one. I'm linking it as it has a simple wiring diagram. (Shelly is the control equipment)
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