Wiring New Cooktop

Putting in new counter tops and also put in new electric cooktop in a early 70's house. The old cooktop had red, black, & white wires. I understand the white wires are for 110. I think the old cooktop was a 120/240 top.

The new cooktop has red, black, and green wires. It is 240/208 V, 60 hertz.

The wire coming in from the wall is a 220 with red, black, and bare. The bare does not appear to be copper. It is a thick stranded type wire, kind of twisted, appears to be aluminum???

The advice I got was to go with red/red, black/black, and green/bare. I used the previous wire nuts, which are blue. I have read that there are special wire nuts for aluminum to copper. Not even real sure if that is the wiring type I have. I assume since that is what was on the stove previously, more than likely it is safe.

Everything seems to be working okay. But am still a little worried that it wasn't wired properly. Does everything sound okay to you guys? Any additional advice?

The thick twisted (stranded) stuff might be tinned copper. I don't know which would be more unusual -- tinned copper or stranded aluminum. Try scraping it with a knife and see if copper is exposed. You should also look at the other end of the cable (in the circuit breaker box) to confirm where the mystery wire is connected -- ground or neutral. Sounds like it should be grounded, but it may have been connected to the neutral before. If you can find an exposed piece of cable long enough to read the labelling on it, it will tell you exactly what it is.

The OP mentioned that the house was built in the 1970 era. More then likely the house may have AL wiring in it.

wire

The sheath on entrance cable was always aluminum. What color was the metal in the red and black cables? Even now, high amperage units can have aluminum feeds.

It is likely that the wire is tinned copper. The wire you have is from the days when a 240 volt range circuit could be powered by two hot (uncgounded) conductors and a grounded neutral.

That circuit is still legal for replacement ranges or cooktops if the range ground is connected to the neutral, and the neutral is connected to the ground at the service panel.

If you require a new circuit then it needs a ground in addition to the neutral.

The neutral/ground conducts the small unbalanced current associated with lights and controls in a range.

You will need #6 or #8 copper, depending on the kW rating on the nameplate of the range, and depending on whether the circuit also serves an oven.