Wiring a relay?...................

HappyHippyDad · Mar 8, 2023

Hello all..

I have been asked to wire a relay into a FCU for a 3kW immersion.

The plan is for the customer to be able to access the immersion over WIFI.

The relay is a Shelly 1pm WIFI relay, 16A 110V - 240V.

I have not wired a relay before, hence asking on here.

The wiring diagrams on the MI (see pic) show it being used for a light, which will include a light switch. Therefore do I just make a link between the L and SW as seen in my written diagram? Do I need the link, or are these terminals purely so the light could still be used from the switch?

I don't see how I can wire this directly into the FCU for the immersion as the relay has a common neutral, I would therefore loose the double pole function of the FCU. So, I'm assuming the relay would get wired into the load cable coming from the FCU going to the immersion?

Thanks in advance.

[ElectriciansForums.net] Wiring a relay?...................

pc1966 · Mar 8, 2023

What you suggest looks fine to me.

I would put it on the load side of the FCU as you propose as handier for anyone to isolate later, also just to flick off/on if it needs a hardware reset to get connection going again.

snowhead · Mar 8, 2023

If you fit the relay on the load side of the FCU as per your sketchy sketch, then you still have D.P isolation by the FCU.

Do the Shelly relays come with a box, the website appears to show them being hidden inside a continental socket?

HappyHippyDad · Mar 8, 2023

pc1966 said:
What you suggest looks fine to me.

I would put it on the load side of the FCU as you propose as handier for anyone to isolate later, also just to flick off/on if it needs a hardware reset to get connection going again.

snowhead said:
If you fit the relay on the load side of the FCU as per your sketchy sketch, then you still have D.P isolation by the FCU.

Do the Shelly relays come with a box, the website appears to show them being hidden inside a continental socket?

Thankyou both

What do you think about the link between L and SW? Does this look like it is needed? I'm a little worried that this just means the immersion is 'on' all the time?

@snowhead The customer seemed to think they are designed to go into the back box of the switch/socket. This is corroborated by some internet sites. I would rather have it in a separate box as it'll be a bit of a squeeze in the FCU.

DPG · Mar 8, 2023

I don't think you should link L and SL - I think that is to allow an external switch input to control the output.

And I think I'd definitely be putting it in a separate box.

pc1966 · Mar 8, 2023

DPG said:
I don't think you should link L and SL - I think that is to allow an external switch input to control the output.

Looking at the instructions here:

https://shellystore.co.uk/wp-content/uploads/2021/05/Shelly1PM-UserGuide-EN-web.pdf

It seems the L1 to L internal path is for power measurement, and then the L to SW link is for the relay that comes out on the 'O' pin (i.e. SW-O is the relay contacts and L1-L the measurement CT or similar). So it is linked up as it should be.

DPG said:
And I think I'd definitely be putting it in a separate box.

Yes, definitely!

The dimensions of 41 x 36 x 17 mm suggest it could go in a 25mm deep back-box with a blanking plate as a cover, maybe even a 1+1 back-box so FCU through the the relay unit all in the one area?

Rockingit · Mar 8, 2023

DPG said:
I don't think you should link L and SL - I think that is to allow an external switch input to control the output.

And I think I'd definitely be putting it in a separate box.

That's also my take on it - it's basically a manual override so needs to be kept unconnected (or connected to any old normal switch for use as a manual override, of course.). It's not the clearest of instructions! L1 may need linking to L, too, as I suspect that may be the internal power??

LEGEND:
N - Neutral input (Zero)/( + )
L - Line input (110-240V)/( - )
L1 - Line input for relay power
SW - Switch (input) controlling O
O - Output

HappyHippyDad · Mar 8, 2023

Rockingit said:
That's also my take on it - it's basically a manual override so needs to be kept unconnected (or connected to any old normal switch for use as a manual override, of course.). It's not the clearest of instructions! L1 may need linking to L, too, as I suspect that may be the internal power??

LEGEND:
N - Neutral input (Zero)/( + )
L - Line input (110-240V)/( - )
L1 - Line input for relay power
SW - Switch (input) controlling O
O - Output

I think you may be right.

Other diagrams on the net showed a link between L and L1, this was when it was used to supply a socket.

pc1966 · Mar 8, 2023

Yes, looking at it again maybe that link is not needed. Probably best to play with it before you try to install at a customers site!

I do wonder what will happen when the related 'cloud' service is eventually discontinued?

HappyHippyDad · Mar 8, 2023

Thanks all for the posts.

I did feel a little silly posting as I assumed this was just really obvious. It proves not to be quite so straight forward which I feel a tad pleased about

I shall endeavour to update, although it's not exactly the most exciting of threads.

Dave OCD · Mar 8, 2023

I think I'd have talked her into a simple 24 hour timer, instant wifi access to something that needs a good hour to warm up seems a bit ott.

DPG · Mar 8, 2023

Dave OCD said:
I think I'd have talked her into a simple 24 hour timer, instant wifi access to something that needs a good hour to warm up seems a bit ott.

A good hour to warm up? Ah , wrong thread sorry.

Taylortwocities · Mar 8, 2023

Dave OCD said:
I think I'd have talked her into a simple 24 hour timer, instant wifi access to something that needs a good hour to warm up seems a bit ott.

I agree, Shelly plus relay plus all your time is a hard way to do this.
Buy one of these. Job done

Timeguard Wi-Fi Controlled Fused Spur (Tuya Edition) - FSTWIFITU

(other similar products are available)

pc1966 · Mar 8, 2023

Related to this thread, I looked at there other products and this looks jolly useful:

Shelly Pro 4PM | Shelly Store UK | Smart Home Automation

Purchase Shelly Pro 4PM from the only Shelly authorised reseller in the UK. Shop Wi-Fi smart home automation now!

shellystore.co.uk

I think it can be used with wired networking and no need for "the cloud" so might be handy for small projects needing a degree of automation or power reporting. At £100 or so it is almost worth getting on just to play with!

Dave OCD · Mar 8, 2023

That looks like a very useful product ! Not keen on fused spurs on Immersions though with the full 13 amps being drawn for longish periods. 20 DP switches are better, fed from 16a OCPD.

Wiring a relay?...................

HappyHippyDad

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pc1966

snowhead

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HappyHippyDad

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DPG

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pc1966

Rockingit

-

HappyHippyDad

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pc1966

HappyHippyDad

-

Dave OCD

-

DPG

-

Taylortwocities

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Timeguard Wi-Fi Controlled Fused Spur (Tuya Edition) - FSTWIFITU

pc1966

Shelly Pro 4PM | Shelly Store UK | Smart Home Automation

Dave OCD

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