Need help wiring new baseboard thermostat (Line/Load/Common)?

Question

Hope someone can help out with this. It should be fairly simple. My house is outfitted with very old baseboard thermostats that are functional, but very ugly. I am trying to replace them with new ones, but I'm running into an unexpected problem with a few of them. The old thermostats have 3 wires which are labeled LINE LOAD and COMMON. Some only have 2 wires (which were easy to replace).

The new thermostats I bought have either 2 or 4 wires, so I'm confused as to how to wire these. Is Common just an old term for ground?

Answer 1

A 2 wire t'stat is used for 120 VAC (stat breaks the hot line).
A 4 wire stat is used for 240 VAC (stat breaks both lines-both are hot).
Not sure why your old stats would have a common. Usually only digital or programmable stats have a common. If your new stats are just standard mechanical non-digital or non programmable, you don't need the common-just put a Wire-nut on it.
I haven't seen a standard mechanical non-digital that needs a common.

Answer 2

First you need to KNOW the thermostat specifications - 120VAC or 240VAC operation. This is KEY.

120VAC - load (line), neutral & common (ground), 2 wire & ground

240VAC - 2 load (line) & common, 3 wire

Answer 3

chances are the wires were pulled in series your line wire is the wire that will have power the load wire is the one that will send the power to the unit common is ground /neutral