Products

Motor Protection

Motor Protection

CT7K & CT4 Thermal Overload Relays

Simple and effective motor protection for applications to 10HP @ 460V (15HP @ 575V)

Sprecher + Schuh's economical CT7K and CT4 Thermal Overload Relays share the same excellent protection characteristics as our full featured thermal overload relays, with the exception of differential tripping and selectable reset, yet still trip under single phase conditions at 1.25 x set current.

Consistent and reliable protection

The consistent high quality of Sprecher + Schuh thermal overload relays is ensured by a complex current limiting 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 CT Series have been recognized by many motor manufacturers as the ideal type to assure optimum motor protection.

Ambient temperature compensation

All Sprecher + Schuh thermal overload relays are temperature compensating. 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 -25°C to +60°C.

Single phase applications

CT 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 on page B27.

Convenient dial adjustment of motor FLA

Rather than changing "heaters" to set the overload to the motor's FLA, CT relays have a dial adjustment on the faceplate. This convenience offers a wide range of FLA settings and allows you to accurately set or reset the overload in seconds.

Other standard features

CT thermal overload relays feature a fail-safe "trip-free" design that prevents the device from being held closed during an overload. CT4 and CT7K overload relays feature a manual reset. An optional NO signal contact can be added to the CT4 and CT7K in the field for use as an alarm circuit.