Overload Protection

The CEP7 solid state overload relays offer superior motor protection with advanced features like:

• Selectable trip class and field-installable modules
• A wide current adjustment range of 5:1
• Robust, self-powered design with mechanical and electrical mounting
• Self-sealed latching mechanism

The basic concept of utilizing Application Specific Integrated Circuits (ASICs) results in an affordable solid state overload relay. This kind of versatility and accuracy was simply not possible with traditional bimetallic or eutectic alloy electromechanical overload relays. The CEP7 offers dramatically lower energy requirements that save money and reduce panel space.

Sprecher + Schuh has always paid particular attention to the subject of motor protection. This concern is reflected in our CT7N line of thermal overload relays that include many standard features not available with eutectic alloy overload blocks and heater elements of the past. And, CT7N overload relays are designed to mount directly to the load side of Sprecher + Schuh CA7 Contactors.

Consistent and reliable protection-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 that 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 CT7N 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 CT7N (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-CT7N 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 wiring diagrams library.

Other standard features-CT7N 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 CT7N 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.

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.