Use of Shelly 1PM plus to control water heater

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PSLog

291 posts

Ultimate Geek

#304656 24-May-2023 16:30

I'm planning to use a Shelly PM1 Plus (wifi relay) to control the on/off times of my water heater to take advantage of off-peak electricity tarifs.
I would like to have the ability to force the heater to be ON (over-riding the relay) in case I have wifi issues.

If I wire the Shelly device in, direct from the switchboard supply, it seems that I can use the existing switch (in a socket made up of a switch/cable out configuration) to provide this over-ride switch.

However, someone has told me that is illegal because the hot water cylinder must have a local isolating switch - and not rely on a switchboard circuit-breaker for this function.

Comments?

As an alternative (to installing a second isolating switch) does the Shelly PM1 - Plus's bluetooth function allow the relay to be forced ON?

I know the work needs to be done by a registered sparky - I'm just scoping the details of the job. It may be that, as yet, not too many sparkies are that familiar with these devised yet.

Thanks in advance

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472 posts

Ultimate Geek

#3079448 24-May-2023 18:03

I stuck one on mine, I was also told not to touch the switchboard end. So I chucked it inside a isolating switch outside the house. But my 3KW hot water box/cylinder is outside the house easy access. It has been working fine for over a year. Works with home assistant perfectly too.

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lloydw

21 posts

Geek

#3079454 24-May-2023 18:57

I looked at doing something similar last year, but then read some stories online about them getting really hot when under load for extended periods of time. It’s ideal to have it outdoors like yours, but I was concerned about putting mine inside my already warm hot water closet 😀

PSLog

291 posts

Ultimate Geek

#3079460 24-May-2023 19:34

cruxis:
I stuck one on mine, I was also told not to touch the switchboard end. So I chucked it inside a isolating switch outside the house. But my 3KW hot water box/cylinder is outside the house easy access/p>

So, is that switch an ON override or an OFF override.

An OFF override is no problem legally - whereas an ON override MAY be a problem.

Re-overheating, the PM1 Plus has thermal overload protection. This is different from the one pictured, which it (I think) the PM1.

MadEngineer

4223 posts

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#3079468 24-May-2023 20:17

Well you’re going to be wiring it in series with the existing switch and not removing it so you will still have the ability to control it.

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hairy1

3330 posts

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#3079469 24-May-2023 20:18

I had a sparky wire one into the circuit prior to the switch next the water cylinder. It was acting as an OFF over-ride and all protections are still in place.

I don't like having the PM in the wall and am shortly replacing it with a PM2 Pro in the switchboard after the circuit breaker. This will also act as an OFF over-ride so I will be able to control when the heater is able to heat. I am not removing any switches.

My views (except when I am looking out their windows) are not those of my employer.

mattenz

190 posts

Master Geek

#3080472 28-May-2023 20:04

I have that setup. It works well, to me it's sufficient override for it to default on after getting power, which can be interrupted either by the isolator or circuit board.

Nate001

630 posts

Ultimate Geek

#3080477 28-May-2023 20:20

I tried this a while ago but strongly advise against it.

Long story short, the device cannot handle a standard hot water heater and I lost confidence regarding its safety in my house so removed it.

I logged the device temperature and it shot over 100c when under a 3kW load after 30minutes of constant load. Looking on the Shelly facebook page many people had similar issues and concerns.

Either use the Shelly to control a contactor, or don’t use it all.

PSLog

291 posts

Ultimate Geek

#3080544 29-May-2023 07:57

Really?
Any comments on this?

Nate001

630 posts

Ultimate Geek

#3082553 30-May-2023 20:09

PSLog: Really?
Any comments on this?

Here are two of many threads on the facebook support page with someone running a hot water cylinder using a shelly.

https://www.facebook.com/groups/ShellyIoTCommunitySupport/permalink/5020988484667142/

https://www.facebook.com/groups/ShellyIoTCommunitySupport/permalink/5677050682394249/

eonsim

387 posts

Ultimate Geek

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#3082565 30-May-2023 20:30

@PSLog For high loads you should ideally be using a Shelly EM or 3EM, you use the CT-clamp for power monitoring (and can use the extra one or two clamps to monitor other key circuits, or whole house load) and you get a suitable contractor installed on the hotwater cylinder circuit and linked to the EM/3EM. The EM then controls the contractor to turn on or off the hotwater cylinder, with out putting any load on the Shelly, much safer and no chance of the shelly melting or shutting down due to over heating with a high load, as all the load is going through the contractor which is designed to handle it.

PSLog

291 posts

Ultimate Geek

#3082570 30-May-2023 20:39

Thanks for the replies.
My element is 2kW, giving only an 8.33 amp load.
That is very close to half the rated load for the Shelly.
I'm going to try it, but stick a temperature sensor to the device and monitor it for the first week or so

hairy1

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#3082575 30-May-2023 21:01

The device is New Zealand AS certified for 16 Amps so there shouldn't be an issue with ruining a 3kW heater.

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Nate001

630 posts

Ultimate Geek

#3082577 30-May-2023 21:04

2kW is a lot more manageable. Truth is you don't need a EM device for a fixed size load, you could control it with a standard shelly and simply multiple by the on time for energy usage. This would eliminate the resistive load shunt which generates extra heat.

Klathman

300 posts

Ultimate Geek

#3082648 31-May-2023 09:24

We have a Shelley 1PM on the spa pool and haven't received any over-temperature warning.

It's a 15amp circuit, and we're regularly hitting 2.7-2.9KW while it's heating.

The plug is outside which I guess will help cool it down over the winter though.

Ge0rge

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#3082685 31-May-2023 11:03

One thing I note with these devices is that the maximum conductor cross-sectional area is limited to between 0.5 to 1.5 mm² (from here).

NZECP 51:2001 states that for storage water heaters up to 3kW, 1.5mm² stranded conductors are the minimum. For storage water heaters between 3kW and 6kW, 2.5mm² is the minimum wire size.

I would argue that, based solely on the above, that a Shelly 1/1PM device should not be used for any load above 3kW, unless it is controlling a contactor.

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