Underfloor Heating Control with Relay

[jf93kf]

Hello all. I have underfloor heating installed in my flat which is controlled by an Ambiente UH8DS-SB (https://ambienteufh.co.uk/app/uploads/2019/03/UH8DS-SB-Wiring-Diagram.pdf). I'm trying to build my own smart thermostat with a Raspberry Pi for fun and so have given myself one of the zones to 'play with'. I've got things working well, but I'd like to confirm if what I've done is safe from an electrical perspective.

Simply put, I'm trying to use the Raspberry Pi connected a relay to turn the zone on or off.

The UH8 has different zones, each with a live, timer 1, timer 2, earth, neutral and switched live cable (see wiring diagram above). Originally these cables went to the thermostat in my zone, but I've removed them so I can control things with a relay instead. I've now got a live cable coming out of the UH8 going into my relay's common terminal hole. I've also got the switched live cable coming out of the UH8 going into my relay's NO (normally open) terminal hole. When I energise the relay, the circuit is closed and the UH8 switches on the power to my zone.

It works perfectly, but my question is: is this safe? The earth and neutral terminal holes on the UH8 are now empty and aren't required for my purposes as far as I'm aware. My thinking is that these are required to power the thermostat when installed traditionally, where the switched live is used to turn the heating on but I can get by with just powering on the switched live with the relay.

Have I made any silly or dangerous assumptions with this setup please?

Before:

After:

 

[jj4091]

To me instead of "I'm trying to build my own smart thermostat " you have just introduced a smart switch unless the circuit you have built into the raspberry pi includes a thermostat that is going to be in the room with the heat source.
" Simply put, I'm trying to use the Raspberry Pi connected a relay to turn the zone on or off." That isn't a thermostat.
Or am I completely misunderstanding what you are saying.

 

[jf93kf]

Ah sorry, perhaps I wasn't clear in my post. I've also used the old thermostat wiring to connect a temperature sensor in the room which is then connected to the Raspberry Pi. The Raspberry Pi then runs a program to turn the relay on when heat is required. I just tried to keep my description simple because all I'm asking is if the way I've wired the wiring centre to my relay is safe and correct? The 'smart thermostat' part was just context but I'm asking about one part of the system. Hopefully that makes sense?

 

[jj4091]

OK so as long as the normally open contacts on the relay have the current carrying capacity for the element it's controlling and preferably a bit extra, it looks ok to me. Presumably the coil voltage for the relay is not 230vac but a low dc. as you do not show an earthing arrangement in your diag.

 

[jf93kf]

Thanks for your reply. Yeah I checked and the relay is rated for 250V and the coil voltage is low dc from the Raspberry Pi. Thanks for your help!

 

[jj4091]

It's not the 250v you need to check it's the current carrying capacity of the contacts

 

[jf93kf]

Oh I see. thanks for pointing that out. So my relay can handle loads up to 5A 250V AC or 5A 30V DC. The UH8DS-SB wiring diagram only mentions 230V AC supply. The existing thermostat that was connected lists the following:
Input: 230VAC 50/60Hz
Output: 230VAC 3A MAX

Given that that thermostat used to be plugged into the contacts that I've now attached my relay to, in my mind that suggests that the existing current was 3A so my relays would be fine.

It seems odd that the wiring diagram doesn't list the max output current. Am I missing something that I need to read up on? Thanks

 

[jj4091]

It seems your relay should be okay, but if it fails prematurely look for one that can handle a higher load

 

[jf93kf]

Excellent, will do. Thanks for your help working through this!