Shelly 1PM Plus 16A Relays on a 20A Circuit

Manion

Hi,

I'm thinking of using Shelly 1PM Plus 16A Relays to smart control two gang sockets in my home. The breaker is rated to 20A and this is giving me pause. The sockets themselves are only rated to 13A (Apparently this is typical?). From reading about, if I make the Live connection via a wago as oppose to using the second (or third) Live terminal on the Shelly as an output to the next socket, it should be fine. Anyone else every do something like this?

https://www.shelly.cloud/knowledge-base/devices/shelly-plus-1pm/

Jonathan

Could you achieve the same thing in a safer manner with smart plugs?

Manion

Not sure smart plugs would be safer, best I've seen are rated to 15Amps and the ones I've used tend to get fairly hot. The Shelly has over power, over voltage and temperature protection.

Manion

I went a head with this, been working away fine for the last week. One flaw in my approach is that I need internet access to activate the relays. I had expected that they could be controlled over lan but that that doesn't seem to be the case. They do have individual access points but I disable those as a matter of course.

emaherx

16Amp devices on a 20Amp circuit should be fine but should be protected with an appropriate size fuse.

Shelly switches do work locally without internet access, via their web interface, also via MQTT and HTTP requests. I don't use the Shelly app or Shelly cloud at all but Home Assistant and Node-Red along with any number of home controllers work with them locally.

Manion

The devices plugged into the outlet are all 13 amp fuses and Ive configured the Shelly itself to have a 13amp max draw so even if two devices are plugged into the socket the max it will provide is 13 Amps.

IMG20221112112423.jpg

I've only been using the Shelly app so far, which doesn't appear to work without an internet connection. I've it on my to-do list to get up and running with home assistant, at which point so hopefully that will solve the control issue.

emaherx

https://www.boards.ie/discussion/comment/119881380#Comment_119881380

I've never used the App, but probably makes sense that you need some kind of broker to manage multiple switches, shelly cloud is the obvious simple solution for their app. Home Assistant is a good choice for a local broker and has the added benefit of being able to add devices from multiple other brands.

Manion

I have a few Shelly EM devices, I noticed that on some of the circuits there can be a very small negative power usage recorded when the appliance is not on. For instance my heat pump is reading at -7 watts. Does anyone know what's causing this? I guess this is due to some inductive components in the appliance?

cromelex

https://www.boards.ie/discussion/comment/119888769#Comment_119888769

I see the same with my Shelly EM, on the heatpump it registers -3 or -4 watts when it's off.

What I'm doing in home assistant is using a template sensor which goes to 0 when the power usage is negative.

2011

https://www.boards.ie/discussion/comment/119880977#Comment_119880977

Yes, it will "work" bu the MCB rated at 20A will no longer provide adaquate protection to the downstream circuit in the event of an overcurrent condition. To comply with the regaultions and more importantly to protect the circuit there are two choices:

1) Change to MCB's with a 16A rating (B type)

2) Get the Shelly to switch a contactor rated at 20A or more.

This is why an instantaneous shower or electric cooker typically uses isolators rated to switch 40A or more.

Manion

I'm unsure I follow you second point. "2) Get the Shelly to switch a contactor rated at 20A or more." the shelly is the relay, it's an internal limit. I do think I'm OK as the Shelly itself does have overcurrent and overvoltage protection and I've configured it to cut out at a lower current value (13amps). I've also connected the new sockets via a Waco.

emaherx

https://www.boards.ie/discussion/comment/119983071#Comment_119983071

Doubt that function is rated as a current limiting safety device, your insurance may be at risk if not adequately protected. Personally I'd put a fuse to protect the Shelly itself.

Manion

What do you meant a fuse to protect the Shelly.

emaherx

I mean it is not designed to be put unprotected on a 20A circuit. All devices on your 20A are usually protected by a fused plug, hardwired devices should also be protected by their own fuse.

The Shelly is not considered a current limiting safety device and should not be used as such. A fault condition in the Shelly itself may not trip the 20A circuit before it bursts into flames, your first post obviously makes you suspect this yourself. Adding in a suitable fuse would not be difficult or expensive and may save you from a fire (or in worst case scenario leave you insured).

Manion

The last bit of your post is the bit that I don't quite follow. There are RCBs in the consumer unit and replacing one of these would require a electrician as it would come under restricted works. Also it would trip all the time. Beyond that anything plugged into the socket has a 13 Amp fuse. So I'm missing where you'd add another fuse.

emaherx

The Shelly itself is not protected, the fuse is needed on its own power supply. You'd use it inline so no need to go near the circuit breakers or reduce them or to effect the rest of the ring main in any way. I'd use one of these at least.

Funny enough Shelly themselves show in the wiring diagram for the 1 pro some fuses for load and PSU, they should have included them in the diagrams for all of their products.

Also bear in mind that 16A rating is for resistive loads, it's only 8A for inductive loads.

I also have serious doubts over it's ability to power large continuous resistive loads for hours at a time and last very long, I wouldn't recommend a shelly without a contactor to switch any heaters or immersions by itself.

Manion

Ok that makes sense. Not sure about the Shelly Pro, those are consumer units modules.

emaherx

Don't worry about the pro bit the point remains the same, the fact is even the Pro Din mounted devices require appropriate fuse or breaker protection. And your device may be slightly different if it shares live/neutral with the relay and its own PSU but it should still be protected by an appropriate size fuse. The reason our plugs have fuses is the 20A breaker is to protect the entire circuit from overload but is too high for the individual devices.