Earth required or not on heat call wiring center

[RuraidhBoy]

I was setting up a heatmiser UH8 wiring centre tonight and the boiler has a 230v output terminal for connecting to ac devices. The call for heat on the boiler is L/SW Live on another terminal and is volt frree

My plan was to use a 5 core from the boiler to the wiring centre, but when I looked at the heatmiser wiring diagram, its showing an earth between the boiler and wiring centre for the heat enable connection.

Is this earth necessary for the boiler enable? I've seen other wiring centres don't have this - even other heatmiser wiring centres dont.

Cheers

 

[newfutile]

Even if its not used every point should have a cpc

 

[Avo Mk8]

If the boiler and the Heatmiser UH8 both have their own solid connections to your installation earth, which they should through their mains leads, then I don't see that the heat enable earth is essential.
I have two UH8 in service here. There is no terminal for a 'Boiler Enable' earth, so to implement it, you would be adding an extra wire to the UH8 incoming earth terminal, only to run it back to the boiler which already has (the same) earth connection already.
Maybe the earth for 'Boiler Enable' is illustrated to cover some specific situation that Heatmiser have identified, like when a stand alone accessory, e.g. RF module, is providing the boiler enable switching.

 

[RuraidhBoy]

If the boiler and the Heatmiser UH8 both have their own solid connections to your installation earth, which they should through their mains leads, then I don't see that the heat enable earth is essential.
I have two UH8 in service here. There is no terminal for a 'Boiler Enable' earth, so to implement it, you would be adding an extra wire to the UH8 incoming earth terminal, only to run it back to the boiler which already has (the same) earth connection already.
Maybe the earth for 'Boiler Enable' is illustrated to cover some specific situation that Heatmiser have identified, like when a stand alone accessory, e.g. RF module, is providing the boiler enable switching.

Correct and agree with you. This is a newer iteration of the standard UH8 wiring centre but they never mentioned why the earth is there in their installers manual. I had a good look around the pcb it looked like nothing more than a placeholder connection. I contacted heatmiser to ask if there was some fault with the PCB but they confirmed the earth is in fact a placeholder connection. They said they added the earth connector because a lot of sparks and heating engineers were running a 2 core and earth between the heat enable and boiler and terminating the trailing earth into a wago or similar. So, to make life easier for installers they added it to the PCB, but it essentially isn't required. They said it's caused confusion and a lot of calls and they will update asap.

Personally, I don't see the point of adding an extra earth terminal to the volt free side. It's not something I would have designed in. I would have specified a 5 core cable and shown this in the wiring diagram. They also said the LR-LS labelling has caused confusion and they're looking at labelling everything as COM/NO/NC in future models.

 

[littlespark]

The earth wire is classed as a “cpc”…. In other words, the Circuit Protective Conductor.

Every cable that runs mains voltage should have an earth cable in it, to protect the cable if someone inadvertently cuts through it.

Many heating sensors and actuators may run on extra low voltage nowadays and do not require an earth, but the majority of existing systems do.


One reason could be that because heating controls tend to need 4 or 5 core flexes between, by using the earth core as an earth, it takes away the temptation of using it as a switchwire, and paying for a core less than you need.

 

[RuraidhBoy]

Every cable that runs mains voltage should have an earth cable in it, to protect the cable if someone inadvertently cuts through it.

The manufacturer's have confirmed it's not required see above. Also, watch the sequencing in this video -

View: https://www.youtube.com/watch?v=nOQ8ZEhSLDI