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!

 

[Strima]

The NEST ring IIRC is extra low voltage around 12 volts.

I would recommend you get an electrician in who's competent with NEST to install it for you.

 

[littlespark]

Oops
I don’t know nest completely, but I think you put 230v across something that’s designed for extra low voltage.

As @Strima beat me to it.... 12v

you’ve cooked the Nest.

 

[Michael Simons]

Oops
I don’t know nest completely, but I think you put 230v across something that’s designed for extra low voltage.

As @Strima beat me to it.... 12v

you’ve cooked the Nest.

Thanks! I thought as much. So the unit that is currently there also has a 16A blue and brown wire - is that the 12v supply I am after?
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Thanks! I thought as much. So the unit that is currently there also has a 16A blue and brown wire - is that the 12v supply I am after?

No thats the output. Just going to faceplate the wall and move on with my life I think. Cant get an electrician round at the moment anyway.

Thanks anyway chaps

 

[littlespark]

Your old controller would have a live and neutral feed, at 230v mains, and a switched live and neutral going to the heating.. (marked at 16A there) There’s also connections there for sensor... which would be a thermostat to turn the heating on and off.

Best advice I can give right now is for you to connect each of those wires into individual connectors, and leave the circuit turned off until an electrician can come look at it.
Throw the nest in the bin. It’ll still smell of burned electronics for a few weeks.

 

[freddo]

The old heating mat appears not to be earthed which is also not good.
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I am buying a new back ring

If the nest controller was plugged into the back plate it will also need replacing.

 

[Michael Simons]

The old heating mat appears not to be earthed which is also not good.
[automerge]1587989879[/automerge]

If the nest controller was plugged into the back plate it will also need replacing.

It still functions but says it needs "reconnecting". Cant buy the back ring on its own anyway so have to buy a whole new unit.

No surprise it isnt earthed - bought the house off a cowboy!
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Your old controller would have a live and neutral feed, at 230v mains, and a switched live and neutral going to the heating.. (marked at 16A there) There’s also connections there for sensor... which would be a thermostat to turn the heating on and off.

Best advice I can give right now is for you to connect each of those wires into individual connectors, and leave the circuit turned off until an electrician can come look at it.
Throw the nest in the bin. It’ll still smell of burned electronics for a few weeks.

Thanks for this.

I am ordering in the parts so that my sparky can sort once lock down is over.

Is this what he will need to step down the 230v to 12v?

https://www.NoLinkingToThis/p/aurora-12-240v-constant-voltage-led-driver-16w/2107t

Thanks

 

[Strima]

It still functions but says it needs "reconnecting". Cant buy the back ring on its own anyway so have to buy a whole new unit.

No surprise it isnt earthed - bought the house off a cowboy!
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Thanks for this.

I am ordering in the parts so that my sparky can sort once lock down is over.

Is this what he will need to step down the 230v to 12v?

https://www.NoLinkingToThis/p/aurora-12-240v-constant-voltage-led-driver-16w/2107t

Thanks

No, the Nest thermostat will either gets its power from a 5 volts USB supply or direct from the Nest heatlink system of you want it hard wired.

 

[Michael Simons]

No, the Nest thermostat will either gets its power from a 5 volts USB supply or direct from the Nest heatlink system of you want it hard wired.

Ok understood.

SO I have the heatlink in the boiler cupboard and theres no point putting the thermostat there hard wired into the heat link as theres no radiator in that room so itll never know when to turn the heating off.

Ideally the thermostat will go in the hall but there is no plug to plug it into - seeing as I have an open cavity with the wires there is there really no way to step down the 240v to 12v? Would I be better finding a USB unit that I can connect to the 240 and then just bury it in the wall? There is plenty of space.

Thanks

edit: something like this?

5 720 78 | Legrand White 1 Gang USB Socket, 2.4A, Indoor Use | RS

uk.rs-online.com

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The old heating mat appears not to be earthed which is also not good.
[automerge]1587989879[/automerge]

If the nest controller was plugged into the back plate it will also need replacing.

Is the controller definitely going to be dead as well? It is powered on but keeps saying "disconnect from back plate". Surely if it was dead the screen wouldnt work?

Nest have kindly sent me a free back ring - just trying to make sure I dont need a whole new unit otherwise will just order one now rather than wait for new ring to find out its beat.

thanks!

 

[freddo]

I'm surprised it is doing anything at all! You might be lucky. You can power the nest from the T1 and T2 terminals, you need a 12V DC power supply. You can buy 12V power supplies that will fit inside UK back boxes. I have a similar one powering my Evohome heating controller.

 

[Michael Simons]

I'm surprised it is doing anything at all! You might be lucky. You can power the nest from the T1 and T2 terminals, you need a 12V DC power supply. You can buy 12V power supplies that will fit inside UK back boxes. I have a similar one powering my Evohome heating controller.

Great thanks. Will try to find one small enough to sit back there.

Thanks freddo

 

[Strima]

The Nest thermostat doesn't need to go where the existing controller was. You can buy a stand so it can sit on a shelf or desk in any room you want.

 

[hasel5]

as said before think you should employ a electrician

 

[Michael Simons]

The Nest thermostat doesn't need to go where the existing controller was. You can buy a stand so it can sit on a shelf or desk in any room you want.

I know. I have the stand. But due to the config of the house (and amount of open windows and closed doors) the best place to have the thermostat is coincidentally in the hall where the old one was. It seems to keep the house at a constant temp rather than in any of the other rooms.

Thanks
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as said before think you should employ a electrician

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 messed 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

 

[hasel5]

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

 

[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.