Will have to come up with a new topic other than on MOV's, but it is certainly interesting.
Funny, you think you understand something, a bit, and then realize how you really don't.

Anyway -

As I mentioned in my previous post, will be putting in a "secondary" wired-in surge protector (an Intermatic AG 2401 IND )
to try and protect a new furnace circuit board that is apparently susceptible
to lightning induced transients. It fried during last lightning storm.

Eventually, the electrical service box will be replaced with a new one. When it is, will install a whole-house variety. But for now, will have to settle for the point-of-use, wired in variety.

There is the typical on/off AC power furnace switch located in an EMT tubing run, about a foot or so from the furnace proper. This seems like a good place to wire it in, and install it.

Have been thinking about whether it makes more sense to wire it in on the upstream side of the switch, or whether it should be placed on the downstream side (the end closer to the furnace) ?

Seems to me that it probably doesn't matter at all, but thought I'd ask.

Any thoughts on ?