how to connect a Nest 3rd Generation

stem · 12 Jan 2020

OK thanks, good job I checked. In that case

To remove the old thermostat find the origin of the black and grey wires in this cable that you have highlighted...

...where they terminate at the wiring centre on the left in your photo. Note where they go, and then remove the old thermostat cable and the old thermostat receiver completely. Then join together the two terminals where you have just removed the black and grey wires from.

The brown and blue L & N wires are just disconnected.

RSW2020 · 14 Jan 2020

Can I just check if this is correct before I switch my electric back on? Im not wiring the Nest thermostat to the existing thermostat, it will be freestanding and plugged into the mains. I have run 2 small wires. One from L to 2 and the other from L to 5.
Where I have removed L1 and LX from the wiring centre, now has nothing there, but wires running into it?

RSW2020 · 14 Jan 2020

I forgot you said to link the 2 terminal where I removed the wires, I did that and it's all fully functional! I can not thank you enough for all your help!!! You're an absolute star!!!

stem · 14 Jan 2020

Excellent and well done for working that out.

Just a couple of small observations, to avoid the potential for a short circuit, there shouldn't be quite so much copper sticking out of the terminals, (the L in particular is a bit exposed, perhaps running L to 2 and then a separate link from 2 to 5 would have made it easier that inserting all 3 wires into L) and the outer sheath of the cable should be secured under the cable clamp not the individual wires.

RSW2020 · 14 Jan 2020

Thank you! I'll isolate the power for tonight and rewire it properly tomorrow. Thanks again for the help, you've saved me a small fortune!!!

stem · 14 Jan 2020

Excellent. Here's an example that's shows good terminations, and the L-2 and 2-5 link.

Don't go to the other extreme though and have the insulation inserted into the terminal otherwise it might not make a good electrical connection. Heat links can be tricky, those of us that have done a few still sometimes find the connections fiddly.

RSW2020 · 14 Jan 2020

I've just changed that now, thank you. They certainly dont leave any room! I see on your pic, the cable has been fed through the back of the heat link. I'm unable to do that (I dont think) as all the cables from the wiring centre are external and I assume those are internal?

stem · 15 Jan 2020

That's an alternative method of installation. Where cables come through the back of the Heat link they are concealed, are out of the way and there is no danger of them being pulled.

On the other hand, when a cable is external and exposed like yours, there is a danger that it could get caught and the wires pulled out of the terminals. The clamps at the bottom are provided by Nest to secure the cable's outer sheath and stop that happening.

I went to a house a bit back where the owner had caught an unsecured cable in the airing cupboard with a coat hanger hook and ripped the live wires completely out of their terminals. On another occasion a guy did a similar thing in a understairs cupboard when he pulled out some tools and a cable at the same time.

RSW2020 · 15 Jan 2020

Thank you for all your advice, you've been amazing! Now I know that every thing is wired correctly, I'll shorten some of the wires and rewire it, so the cable is tucked inside.

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