Blew The Fuse Connecting NEST to Mains

[Michael Simons]

Hello.

Hopefully someone can help.

My underfloor heating died recently (due to the heating mesh rather than the wiring) and I can't fix it without lifting the floor in the bathroom.

So I have a useless control panel on the wall that I no longer can use and wanted to mount my Nest there instead as its been running on USB since I bought it in the kitchen.

So I took the two wires marked in the photo out the back of the underfloor heating control unit and put them into T1 and T2 as shown in the Nest back ring photo.

When I flicked the switch on, the circuit blew, black electrical dust all over the Nest unit (which appears to now be dead) and the main fuse switched off too.

I am buying a new back ring but wondered if someone could tell me a) why it blew and b) what wires I should use to power the nest from mains? Hoping to not blow up the second unit when it arrives!

Thanks!

 

[davesparks]

agreed and I will. However if there is a simple elegant solution whilst lockdown is happening then I am happy to explore it. Yes I may have f***ed up with the voltages, but I am capable of rewiring a plug and a transformer in if thats all it is. I am all for professional help but no need to pay if its a really simple thing to do. And all I am doing now is ascertaining whether it is a simple thing to do or not.

Appreciate the advice. Ty

It is only simple if you know how to do it.

 

[hasel5]

Just reread the post and I am out

 

[Michael Simons]

The wiring to your under floor heating has no way of controlling your heating end of

who said it did?

i just want to run the nest off the main circuit that the underfloor heating used to use.

 

[hasel5]

Think you should read manufactures instructions and installation advice that come with the nest and then decide on way forward.

The nest comes with a set of instructions to correct ways to connect and set up. if you decide to ignore this this and go your own route then you will void warranty and also your house insurance if something goes wrong with what you do.

 

[Ziggie]

Lets document connections for power.


Connector marked N neutral 230Volts from mains fuse.
Connector marked L LIve 230Volts from mains fuse

Connector marked 2 Live 230 Volts taken from connector marked L
Connector marked 5 live 230 Volts taken from connector marked L or 2

These connectors are all live at all times Nest is working.

Connectors T1 and T2 are to allow the existing cables to your room thermostat to provide power to the Nest Room Thermostat.
BUT BUT they provide power at 12 Volts. Do NOT use the wiring to the existing thermostat without disconnecting the wires from the existing connections in the control box as they will provide power at 230 Volts and the Nest Thermostat will go Bang.

The Nest Thermostat can also be powered from the USB power supply independently of the wiring.

Hint you can run the system without disconnecting the existing thermostat provided:

• you use the USB adapter to power the Nest room thermostat
• you turn up the existing thermostat to a high termperature so that it demands heating all the time.

Hope this helps.