Motor Protection

CT8 Thermal Overload Relays


Overload Protection

CT8 Thermal Overload Relays

Simple and effective motor protection for applications to 12 Amps

Consistent and reliable protection

The CT8 is an economical thermal overload relay that includes standard features like "Differential tripping", Automatic/Manual reset modes, and isolated alarm circuit contacts.

The consistent high quality of Sprecher + Schuh thermal overload relays is ensured by a complex current calibration procedure performed after each unit is at full operating temperature. Calibration is performed at the largest and smallest current the overload can handle. The accurate time/current characteristic curve obtained in this manner guarantees reliable motor protection every time.

Superior Class 10 characteristics

Today's T-Frame motors have less copper and iron than the old U-Frame motors that were popular when traditional Class 20 overload relays were designed. For this reason, faster Class 10 overloads like the CT8 Series have been recognized by many motor manufacturers as the ideal type to assure optimum protection of "T" frame motors.

Protection from single phase conditions

A unique feature not found in traditional thermal overload relays provides accelerated tripping under single phase conditions. This is accomplished with a special "differential tripping" mechanism built into CT8 (see illustration).

Ambient temperature compensation

All Sprecher + Schuh thermal overload relays are temperature compensated. An additional bimetallic ambient compensation strip, built into the conductor- bimetal transmission path, ensures that the tripping characteristics of the relay remain constant over an ambient temperature range of -20°C to +60°C.

Single phase applications

CT8 Series thermal overload relays can be applied for protection of single phase AC motors. The relays have the same characteristics as shown for three phase operation. To maintain these characteristics, each element of the overload relay must carry the motor current as shown in the schematic in the Miniature Contactors and Starters section of the e-catalog.

Other standard features

CT8 thermal overload relays feature a fail-safe "trip-free" design that prevents the device from being held closed during an overload. In addition, a selectable reset button permits either manual or automatic reset modes. A separate NO signal contact is also provided on CT7 overloads which is isolated from the NC trip contact. This permits the use of a trip signal voltage different than that of the control voltage.

International Standards and Approvals

Sprecher + Schuh CT thermal overload relays are UL-listed and CSA-approved. They also carry the CE mark.