Elzapper:
OK, I now know what you mean. (we call them piggy backs, tandems, twins)
To the best of my knowledge, they are all thermal magnetic.
I believe taht "heat build-up" is a major problem with these units, and there use should be severly limited.
I had an instance recently with a 42 circuit panel, that had 20+ "twins" jammed in.
I also have seen "combo" twins...2-2 pole within the space of two normal cb's. factory handle ties on the two center, and the two outer handles; cute..ha??
John
