How to Determine Phase Rotation on a De-Energized Motor

Motor and Phase Rotation Tester: Megger

The Megger 560060 Motor and Phase Rotation Tester is designed to help electrical contractors, industrial electricians, and maintenance technicians determine motor rotation and phase sequence safely and efficiently.

This tester combines motor rotation and phase sequence testing in one rugged, portable instrument. It helps confirm correct phase hookup before a motor is energized, reducing the need for temporary power connections and lowering the risk of incorrect rotation.

Key functions include:

• Complete phase-sequence and motor-rotation testing in one instrument
• Correct phase hookup verification in one straightforward test
• Rugged and portable tester design
• Additional polarity and continuity checks

Description

The Megger 560060 Motor and Phase Rotation Tester allows an electrical contractor or industrial maintenance electrician to permanently connect and tape the terminals of a motor being installed without first energizing the motor through a temporary power source to determine rotation.

This is especially useful where temporary hookups are time-consuming, expensive, or hazardous. The concern becomes even greater when working with large motors or higher-voltage equipment, where trial-and-error testing is not a practical or safe approach.

Some types of drives should never be rotated in the wrong direction. In these cases, using a temporary hookup or trial method creates a 50/50 chance of incorrect rotation, which can cause serious damage. The Megger tester helps avoid that risk by identifying motor rotation before the motor is energized.

The three motor leads on the left side of the tester attach to the terminals of the motor being checked for rotation. Fuses are included in the motor A and C test leads to help protect the user if those leads are accidentally touched to an energized circuit. These standard fuses can be removed and replaced from their panel-mounted holders.

The three lines on the right side of the tester are used for direct attachment to energized AC power systems up to 600 volts to determine system phase sequence.

A four-position switch selects the test being performed:

• System phase sequence
• Motor rotation
• Transformer polarity
• Off position

The selector switch connects a D-size dry cell into the circuit when checking motor rotation or transformer polarity. In the OFF position, both the meter and the battery are disconnected from all circuits.

A push switch is connected in series with the battery and opens the circuit during transformer polarity testing. The dry cell can be removed and replaced from its panel-mounted holder using a coin-slot access cap.

The DC zero-centre ammeter indicates correct or incorrect rotation or polarity by deflecting its pointer to the right or left. A zero/null adjuster is also provided for the ammeter.

Applications

The Megger Motor and Phase Rotation Tester provides a reliable way to identify the leads of a disconnected polyphase motor. It also identifies the true phase sequence of energized 60 Hz AC power lines up to 600 volts.

Both checks are important when confirming that a motor will rotate in the intended direction once energized.

The tester also has three additional uses:

1. It can determine the polarity of power and instrument transformers.
2. It can identify phase and polarity of winding sections in multiple-winding motors, including delta- and star-connected motors.
3. It can be used as a continuity tester when checking electrical circuits.

For Canadian industrial, utility, and electrical maintenance teams, this type of tester is useful anywhere motor direction matters before startup, including plants, refineries, mills, manufacturing facilities, water treatment sites, and field service environments.

Features and Benefits

The Megger Motor and Phase Rotation Tester can be used to:

• Determine rotation direction of one-, two-, or three-phase motors before connection to line power
• Determine phase rotation or phase sequence of energized power circuits
• Determine polarity of instrument and power transformers
• Determine phase and polarity of unmarked motor windings
• Identify true phase sequence of energized AC power lines up to 600 volts
• Test higher-voltage systems by using a suitable step-down transformer
• Help reconnect motors where connection diagrams are lost or terminal markings are missing
• Support continuity checks in electrical circuits

This makes the tester useful as a single instrument for several electrical checks. It can identify the leads of a disconnected polyphase motor so that when the motor is connected in ABC phase rotation, or CBA with a modified procedure, it will run in the required direction.

The tester can also identify phase rotation of energized AC power lines up to and including 600 volts. Additional uses include transformer polarity testing and electrical continuity testing.

Where motor connection diagrams are lost, damaged, or unavailable, this instrument can help identify phase and polarity of winding sections before a motor is reconnected.

Theory of Operation

When direct current is applied to the windings of a polyphase induction motor, a magnetic field is created and the rotor iron becomes magnetized. If the magnetized rotor is turned, the magnetic field rotates with it briefly because of hysteresis in the iron.

This movement induces voltage in the windings. The direction of the induced voltage depends on the direction of rotation.

The same principles that determine the direction of a rotating field in a connected motor also determine the direction of voltage induced when the motor is manually turned while connected to the motor rotation circuit. The motor rotation circuit uses these principles to determine motor rotation.

The circuit operates as a bridge in which two adjacent phase sections of the motor winding are balanced against a potentiometer. In the simplest case, where each phase section is represented by a single coil side, the zero-adjust potentiometer is set so that the meter reads zero current while the rotor is at rest.

At this point, the voltage across each of the two phase sections is equal.

When direct current enters one phase and leaves an adjacent phase, a magnetic field is established. When the rotor is then turned from one phase toward the adjacent phase, voltage is induced in the first phase in the opposite direction to the direct current. Voltage is also induced in the adjacent phase, but in the same direction as the direct current.

Where the induced voltage opposes the direct current, it reduces the total voltage across that phase. Where the induced voltage supports the direct current, it adds to the phase voltage.

Because the phase voltages were balanced before rotation, the added voltage in one phase and reduced voltage in the other create an imbalance in the circuit. This imbalance drives current through the meter and produces a correct or incorrect indication.

If the motor is connected to a polyphase power system so that A phase follows C phase in an A-B-C sequence, the rotor will move in the intended direction. Therefore, when the tester gives a correct deflection, the motor tagging indicates the proper phase connections.

This same theory can be applied to more complex windings, including two-pole, three-phase, star-connected motors and delta-connected motor configurations.

Why This Tester Matters

Incorrect motor rotation is not just a minor inconvenience. In many applications, it can damage equipment, create downtime, or compromise safety. Pumps, fans, compressors, conveyors, and certain drive systems may be highly sensitive to rotation direction.

A motor and phase rotation tester gives technicians a safer and more controlled way to confirm rotation before energizing the motor. This reduces reliance on temporary hookups and helps avoid unnecessary risk during installation, maintenance, or troubleshooting.

For Canadian electrical contractors and industrial maintenance teams working in demanding environments, the Megger 560060 offers a practical way to check motor rotation, phase sequence, transformer polarity, winding identification, and continuity from one portable instrument.

Product Availability

JM Test Systems offers the Megger 560060 Motor and Phase Rotation Tester for purchase and rental.

Calibration services are also available to support test equipment accuracy and documentation requirements. JM Test Systems has provided calibration services since 1982 and supports customers with traceable calibration services and accredited quality systems.