wrote:

The discussion of the device in series with the Cannon XLR jogged
my memories of the Polyswitch, a protective device whose resistance
jumps up when sufficiently heated (via current), but goes back down
when it has cooled off.

http://www.te.com/usa-en/products/ci...e-devices.html

We ended up not using them, but now I am curious if they show up in
damaged equipment.

** Polyswitches are damaged ( blown apart) by overvoltage when in the high resistance mode. The maximum ratings vary from 16V to 250V AC for different devices.

Polyswitches are in fact *temperate operated* so will switch at lower current when the ambient temp is higher than rated, usually 20C.

Another issue is that returning to the original low resistance value after cooling can take some time, days even - meanwhile the trip current will be lower than before.

Good practice is to make the trip current occur at double or more the normal running current and also allow for the effect of a hot environment.



... Phil