Question about replacing line voltage thermostat

thinksincode · 01-11-2012, 04:25 PM

Hello DIYers,

I am attempting to replace a line voltage thermostat for my electric baseboard heater. I had a few questions, please bear with me:

The old thermostat has screw terminals where the wires attached (photo #1), but the new thermostat (photo #2) has wires directly attached. How should I attach these wires to the wires in the wall - wire nuts?
The old thermostat had a green grounding screw, but I don't see any such thing in the new thermostat (photo #2). Where does the ground wire from the wall need to go?
I am not sure how the wires match up. In the wall, there are 2 sets of wires - each set has 1 white and 1 black. In the new thermostat, there are 2 sets of wires - but each set has 1 red and 1 black. Does black go to black and red go to white?
There is some green corrosion and some blackening on a few of the wires in the wall. Could this be from moisture? Is the wire still OK to use?
It's hard to see in the photos, but the plastic electrical box in the wall is broken - a piece of the plastic broke off from the main one. Do I need to put a new box in?

Thank you so much - sorry for all the questions, you guys are always so helpful!

// Joe

Doc Holliday · 01-11-2012, 04:30 PM

Yup, cut off the burned and corroded ends of the wires and wire nut the newly stripped ends to the new wires. Might want to 'weather proof' the wire nuts by wrapping them in electrical tape so the nuts stay tight.

Doc Holliday · 01-11-2012, 04:32 PM

You may want to ask in the electrical section of this forum if a junction box or the likes may be needed to contain those wire splices to be up to code. If so that is another can of worms entirely.

biggles · 01-11-2012, 04:59 PM

that looks like 115V in the colors of he wires but that white is taking the same hit as the black and over heating the insulation tell me its 208V/230V total break on power line in.check the amp rating on that new switch vs the old one.taking you into another direction might consider breking that down to 24V with a transformer and regular contactor so you can go with a programmable stat and 24V controlling out of that hole in the wall..just a suggestion

sammy37 · 01-12-2012, 11:23 AM

Yes, put the blacks with the blacks and the reds with the whites. That is a scary mess you got there, I'm curious as to why those wires got so hot, hopefully just a bad connection.
Also from the pic, that junction box doesnt look very deep, would be better if you could replace it with a new deeper one and use proper sized wire nuts on your connections.

sammy37 · 01-12-2012, 11:26 AM

I just looked at your pics again and I can see one reason why the wires got so hot, the wire wasnt really even looped around the screw terminals, just kind of shoved barely into one side.
Make darn sure you clean out the bad section of wire before using it again.