How It Works
Bimetallic Disc Creep-Action Switching
Series 11 temperature switches use a PEPI creep-action bimetallic disc — two metals with different thermal expansion coefficients bonded together — that deforms progressively as temperature changes, opening or closing an electrical contact at a factory-set trip point. The mechanism is entirely mechanical and requires no external power source.
- ✓16 factory-set setpoints — codes A through P covering 0°C to 100°C. Opens-on-rise and closes-on-rise. No field adjustment required.
- ✓Close-on-rise & open-on-rise — both contact forms available. COR activates a circuit on overtemperature; OOR breaks a circuit.
- ✓Built-in hysteresis — the disc resets at a lower temperature than the trip point, preventing rapid cycling near the setpoint.
- ✓Series 10 compatible — same 1/8″ NPT thread. Substitutes into any level position on multi-level extended stem sets.
Creep-Action vs Snap-Action — Which One Your Application Needs
Bimetallic switches come in two mechanisms, and they are not
interchangeable. Series 11 is creep-action. The disc
deflects progressively with temperature and the contact transitions
gradually, giving ±5°C typical accuracy and a slow response.
A snap-action disc stores mechanical energy and snaps
over abruptly at its trip point, giving a faster transition and a
tighter, more sharply defined hysteresis band.
| |
Creep-action (Series 11) |
Snap-action (snap-disc thermostats) |
| Contact transition | Progressive — the disc deforms with temperature | Abrupt — the disc snaps over |
| Response | Slow. ±5°C typical accuracy | Fast, tightly defined |
| Setpoint | 16 factory-set codes A–P, 0–100°C. No field adjustment | Often fixed; adjustable versions exist |
| Contact wear | Slower interruption — more vulnerable to inductive kickback | Faster interruption reduces arc dwell |
| Suits | Overtemperature alarm and shutdown, cooling activation, wetted OEM assemblies in PP/Acetal/Kynar | Tight cycling control where a few degrees matter |
If you need a snap-disc thermostat, Series 11 is not it.
We build creep-action switches. Where the application needs fast,
sharply defined switching within a few degrees, a snap-action device is
the correct choice and we would rather tell you now than after you
specify one. Where a wetted, chemically resistant switch in
Polypropylene, Acetal or Kynar PVDF matters more than transition speed,
Series 11 is built for exactly that.
Creep-action changes how you wire it. Because the
contact interrupts slowly, an inductive load — a solenoid,
contactor or relay coil — sustains an arc across the contacts for
longer than a snap-action device would. Series 11 is rated
6A at 120 VAC resistive and 5A at 120 VAC
inductive, but beyond that, isolate the load with a
Series 50 relay.
See the tech note
Why Bimetallic Temperature Switches Need Contact
Protection in the
Engineering Library.
See Series 10 Integration →
