Line voltage thermostat puzzle

[mdshunk]

Line voltage thermostats (baseboard heat), have their terminals marked "LINE" and "LOAD". While I always observe this instruction, I know that the unit functions either way you hook it up. What's so particular about a set of contacts that close that LINE and LOAD needs observed? I asked several learned coworkers, and the answers ranged from "urban legend", "life of the thermostat may be reduced", and "I don't know. Quit asking so many questions about stuff that don't matter." I have half a notion to tear a thermostat apart, but I figured I'd ask first, to see if someone knows already.

[Wgoodrich]

Look at that thermostat temperature markings. This dictates top of thermostat. Look at line. This line is also placed at the top. Line is supposed to enter at the top of the device to ensure uniformity same as switch on is up not down being uniformity.

Does that hit what you seek?

Wg

[mdshunk]

I generally use White/Rogers or Marley thermostats. On the White/Rogers, all the pigtails come out of the bottom. The outside two are the line, and the inside two are the load. On the Marley stats two pigtails are on the top and two pigtails are on the bottom. However, the left two (facing rear of device) are the line, and the right two are the load. It doesn't really follow any other sort of standard like the top to bottom (as you suggest) like disconnects and switches do. I know it really doesn't matter why, but I wonder about such things.

[Wgoodrich]

Only other engineering design implication that I can think of is the solid unmoving part should be line and the moving part making contact should be load. Don't know this to be a rule but an accepted practice.

Can't think of any other reasoning now that you blew up my last idea. Ha Ha.

Wg

[mdshunk]

Hmmm.... sounds logical. Time to take a hammer to the next bad line voltage thermostat that I replace. Should be soon, since it's winter. I've replaced a couple a week for a while. I seem to get alot of these 10 minute "on your way home, stop here" jobs. I don't mind. I've gotten a few suppers at folks houses when a 10 minute, on the way home job, turns out to be more work than the dispatcher thought it would be. I've always felt that as long as I'm being fed, I can stay and finish. ;)