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3MP SELF-HOLD

MOTOR PROTECTOR

Design & Operating Principles

Applications

Recent history has seen a growing demand for a non-self resetting motor protection device to ensure a high level of safety. Sensata Technologies has

developed the self hold motor protector for both 120 & 250 Vac applications in a wide current range.

The 3MP self hold is used in domestic and industrial electric motors for washers, vacuum cleaners, chain saws, trimmers, lawn mowers and pumps in the 120

and 250 Vac applications.

The heart of the 3MP self hold consists of the pre-set Klixon® snap action bimetallic disc welded into a metal housing with integrated terminal. The

housing is covered by the plate on which a heater can be welded to increase the current sensitivity of the device. A PTC pill is mounted on top of the

metal housing by a clip to meet the requirements for self hold.The combination of a variety of standard terminal configurations and carefully select-

ed materials provides easy handling and mounting. Customized terminal configura-tions are available on request. Wires includ-ing connectors can be

automatically attached to the standard crimp terminals. Sensata Technologies supplies a range of standard leads configurations; customized solutions

are available on request. In construction where the 3MP self hold device is contacting conductive parts of the motor assembly, Sensata Technologies

can deliver the self hold devices with a Mylar™ insulation sleeve. Customized coding and coloring is an option on request.

The operating principle of the 3MP self hold is both simple and effective. The protector is actuated by current passing through it and by the heat

received from surrounding parts.

Standard operating temperature range

from 80°C - 170°C (Increments 5K)

Tolerance on open temperature

± 8K

Peak Temperature (5 Min)

200°C

Ambient Temperature to Guarantee

Stable Self Hold function

0°C

Max. Ambient Temperature

T-Open +20°C

Time Check at T-Ambient 25°C

4 to 10 Seconds Depending on Current Level

Contact Rating

18 A @ cos 0.6 / 250Vac / 300 cycles

SPECIFICATIONS

The electrical circuit is interrupted when the disc reaches its pre-set open

temperature. Due to the heat supply from the PTC pill, the bimetal disc

does not cool down below the close temperature. The contacts will remain

open untill the appliance is switched off by the user, assuring a higher level

of safety. The self-hold condition immediately after the first trip cannot

be guaranteed by the protector itself. This depends on the application in

combination with the selected 3MP self-hold and must be checked during

application verification tests. (same as for winding temperatures). When

switched off the device cools down to a safe temperature again and the

contacts will automatically reset. The bimetal disc provides excellent

thermal and current sensitivity in overload situation. Under locked rotor

conditions the integrated heater in combination with the bimetal disc

provide very accurate trip times for maximum protection.