Measuring the thermal trip point of the low limit snap disc

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Don2222

Minister of Fire
Hearth Supporter
Feb 1, 2010
9,192
Salem NH
In the lab checking out this Magnum CountrySide low limit. This is not the switch that turns the convection blower on, it is the one that shuts down the auger if it does not close at approx 110 - 20 degrees F
See test setup.
Meter set for the lowest 200 ohm scale and reads 1 that shows an open circuit before heat is applied.
After applying heat, when the temp hits approx 117 degrees f the contacts close and the meter reads 0.3 which is essentially a closed circuit and well within the specification of this unit.
Note: If the screws that mount the snap switch are loose then the switch may not trip. Even though this is an air stream mount which has the round protrusion that mounts in the 3/4” hole, most of the heat needed to trip the bimetallic disc comes from conduction and not convection. :)
Anyone else try that?

[Hearth.com] Measuring the thermal trip point of the low limit snap disc [Hearth.com] Measuring the thermal trip point of the low limit snap disc [Hearth.com] Measuring the thermal trip point of the low limit snap disc
 
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Good tip! I haven't had to do that with the pellet stove yet, but I've tested that way on my campers water heater switches before.

Ray
 
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