Note: Disable the motor protection function (L1-0 1 = "0") when using an external motor thermal overload relay. The relay should shut off main power on the input side of the main

circuit when triggered.

Special application precautions should be considered when using motor thermal overload relays on the output of AC drives. The following may occur if

a motor thermal OL relay is connected to the output of an AC drive (between the drive and the motor) when the carrier frequency is high and the wiring

between the motor and the drive is long:

• Thermal relay nuisance trips occur.

• The thermal relay may be damaged due to excessive heat loss.

Some considerations involving AC drives and use of thermal overload relays:

1. Low speed motor operation

2. Use of multiple motors on a single AC drive

3. Motor cable length greater than 50 meters (164 feet)

4. Voltage boost and high torque V/f pattern settings

5. Nuisance tripping resulting from high AC drive carrier frequency

General Precautions to Prevent Tripping of Motor Thermal Overload Relays

Low Speed Operation and Motor Thermal OL Relays

Generally, thermal relays are applied on general-purpose motors. When general-purpose motors are driven by AC drives, the motor current is approximately

5 ~ 10% greater than if driven by the commercial power supply. In addition, the cooling capacity of a motor with a shaft-driven fan decreases when

operating at low speeds. Even if the load current is within the motor rated value, motor overheating may occur. A thermal relay cannot effectively protect

the motor due to the reduction of cooling at low speeds. For this reason, apply the UL-recognized electronic thermal overload protection function built

into the drive whenever possible.

276

L3 L2 L1

A – Ground the cable shield

B – Enclosure panel

C – Metal plate

D – Grounding surface (remove any paint

or sealant)

E – Drive

(Single-Phase 200 V Class)

R/L1 S/L2 T/L3

U/T1 V/T2 W/T3