Earth to insulated box

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I'm building a project that will open the circuit from my thermostat from the boiler when noone is home and the temperature is above 8°C using some 3.3v and 5v electronics connected to a 240v 10A rated relay board.

I've got some heat resistant 5 core (so I can expand to control hot water in future) and have choc blocks at either end to connect to the boiler and the receiver/timer. There's an earth on the boiler and I thought it would be a good idea to connect this to the 5 core and run it to the project box so if the cable was cut and live and earth connected, the rcd would trip.

I'm installing the project in a surface mount double box like you'd use for a double socket, with a blanking plate on the front and plastic rocker switch mounted on the plate so I can bypass the whole project.

I'm not sure what to do with the earth at the plastic box end, if it was a metal box I'd just be bonding to the box, but this seems pointless with an insulating box...at the moment the earth cable will just terminate in the choc block. All the 230V stuff is insulated inside the box, then the box insulates again, does it count as class II?

Thanks in advance!
 
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You have an earth on the input side. If your device has a 230v output, to anything, then the earth must be extended to the device that is being controlled.
 
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You have an earth on the input side. If your device has a 230v output, to anything, then the earth must be extended to the device that is being controlled.
If I'm understanding the description correctly, there's just the single multi-core flex running from the boiler control panel to this unit which is being used to intercept the thermostat wiring to allow the relay in the device to control the boiler, so everything which is being controlled is already in the boiler (or connected directly to it) and earthed that way.

But what is powering this new unit? Is it battery powered, taking a 240V feed to its own internal power supply from the connection to the boiler, or perhaps fed by a separate plug-in power supply?
 
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I'm building a project that will open the circuit from my thermostat from the boiler when noone is home and the temperature is above 8°C using some 3.3v and 5v electronics connected to a 240v 10A rated relay board.
Plan B - buy a programmer which does that sort of thing out of the box..
 

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