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3MP

Motor Protector / Thermal Cut-Out

Design and Operating Principles

Introduction

Applications

The 3MP consists of a metal housing with an integrated terminal. The

housing holds the pre-set Klixon® snap action bimetal disc. The split

plate carries a resistive S-shaped wire which provides additional current

sensitivity. The advanced contact system - one on the bimetal disc and

one on the plate - in combination with the strong disc guarantees a

long life and reliable cycling. The combination of a variety of standard

terminal configurations and carefully selected materials provides easy

handling and mounting. Customized terminal configurations are available

on request. Wires including connectors can be automatically attached

to the standard crimp terminal. Sensata Technologies supplies a range

of standard lead configurations; customized solutions are available on

request. In construction where the 3MP device is contacting conductive

parts of the motor assembly, Sensata Technologies can deliver the devices

with a Mylar™ insulation sleeve. Customized coding and colouring of the

coding tape is an option on request.

The operating principle of the 3MP is both simple and effective. The

protector is actuated by current passing through it and by the heat

received from the surrounding parts. The electrical circuit is interrupted

when the disc reaches its pre-set temperature. As the device cools

down to a safe temperature, the contacts will automatically reset. The

bimetal disc provides excellent thermal and current sensitivity in an

overload situation. Under locked rotor conditions the integrated heater

in combination with the bimetal disc provide very accurate trip times for

maximum protection.

As world leader in appliance motor protection, Sensata Technologies has developed the 3MP for 120 and 250 Vac applications to operate in wider

temperatures and current ranges than offered by existing protection solutions. In providing consistent performance characteristics and excellent

reliability, its features anticipate future technical protection requirements on the AC motor market.

The 3MP is widely used throughout the world in electric motors for washing machines, dishwashers, dryers, vacuum cleaners and industrial applications in the

120 and 250 Vac applications. 3MP features permit to move the motor protector location outside the winding, providing the motor manufacturer extra flexibility

during the manufacturing process. The recent certification as a thermal cut-out device combined with its unique current sensitivity, positions the 3MP as an

advanced and cost effective solution to protect toroidal transformers.