How to Know if Your Motor is Delta or Star [Star Delta explained]

Determining whether your motor is star or delta connected is an important thing to get right, otherwise, you may be needing to buy another motor sooner than you’d expected. Luckily, figuring this out is pretty easy with a few simple steps once you know what to look for.

To identify the motor’s connection type (delta or star), check the nameplate for symbols: delta (Δ) for delta-connected or star (Y) for star-connected motors. Alternatively, inspect the terminal box and you will be able to identify the way the interlinks are configured, 2 links for Star, and 3 for Delta.

In this article, we will look at determining star from delta-connected motors, along with the possible outcomes if this is done wrong, and a delta connected motor is wired in star configuration.

motor

How to identify star delta motor connections

All three-phase motors must come in either a star or delta configuration, with some motors being designed to utilize both by means of different starting methods.

motor maintenance pdf

How three-phase motors work is on the principle of electromagnetic induction and the interaction of magnetic fields. Identifying the configuration of the motor is crucial before energization if you want your motor to live a long and happy life.

Star Delta connections can be determined by inspecting the nameplate

The motor nameplate typically provides valuable information about the motor. The nameplate specifies important electrical ratings, such as voltage and frequency, for which the motor is designed to operate.

It also indicates the phase configuration (single-phase or three-phase) and the corresponding current ratings along with the motor’s wiring configuration. Upon inspection of the nameplate, you will see symbols or markings that indicate whether the motor is connected in star (Y) or delta (Δ). This information is often specified as “Connection” or “Winding.”

As you can see from the motor nameplate below it is a dual-voltage motor that will operate between 220 volts and 480 volts at a frequency of both 50 and 60 Hz.

motor nameplate star/delta
Star/Delta dual voltage nameplate

The values specified next to the delta (Δ) and star (Y) symbols on a three-phase motor nameplate represent the voltage ratings for each respective configuration.

In a delta configuration, the motor is designed to operate on a single-phase supply. This means that the motor is intended to be connected in a delta configuration when it is supplied with a voltage of 220 volts. The delta configuration provides a higher line voltage compared to the star configuration.

On the other hand, in a star configuration, the motor is designed to operate on a three-phase supply at a voltage of 400 volts. This indicates that the motor should be connected in a star configuration when it is supplied with an EMF of 400 volts. The star configuration allows for a lower line voltage compared to the delta configuration.

Check the motor connection inside the motors terminal box

If for some reason the nameplate is not an option, the next thing to do is open the motor’s terminal box, where the electrical connections are made.

By looking inside the terminal box of a motor you will either find a wiring diagram. The diagram should illustrate the arrangement of the motor windings and how they are connected. It will clearly show whether the motor is wired in a star (Y) or delta (Δ) configuration.

If it’s an old motor that’s already wired your working on, you can easily identify if it is star or delta by the configuration of the links joining the terminals.

If there are three links used and they are connected by linking U1 to W2, V1 to U2, and W1 to V2 then it is a delta-connected motor (as shown in the image on the left).

star delta configuration
Delta/Star

If there are only two links used, joining the terminals marked W2, U2, and V2 beginning left to right, it is a star (wye) connected motor (as shown in the image on the right).

Measure the resistance of the windings

Motor windings are continuous coils of wire that when induced with electric current, they set up a magnetic field around the coils. By measuring the resistance of these coils you can determine if you have a star or delta-connected motor.

Once you have the motor terminal box open you now have access to the motor windings where you can measure the resistance between the terminals.

In a star configurated motor where there is a neutral or star point, the resistance (Ω) between any two terminals should read the same, while in a delta configuration, the resistance values will differ slightly due to a continuous loop being formed in delta, rather than each winding having an endpoint in star (wye).

By using a good-quality multimeter set to ohms (Ω) you know if a motor is star or delta by measuring the resistance of each winding. To find out the exact resistance you are looking for you can refer to the motor’s documentation for the expected resistance values.

However knowing the expected resistance values is not necessary, as long as you are getting identical readings across each winding you know the motor is star connected.

testing resistance of motor winding

Remember, it’s crucial to exercise caution and follow safety procedures when inspecting or working with electrical components. If you’re uncertain or uncomfortable determining the wiring configuration yourself, it’s advisable to consult a qualified electrician or engineer for assistance. They can ensure accurate identification and provide guidance based on their expertise.

By using these indicators, you can determine whether a motor is wired in a star (Y) or delta (Δ) configuration, enabling you to make informed decisions regarding installation, troubleshooting, and maintenance.

What happens if you wire a delta motor in star?

Wiring a delta motor in a star configuration can have significant consequences and should be avoided. Here’s what happens when you incorrectly wire a delta motor in star.

If a three-phase motor is incorrectly wired in a star (Y) configuration instead of its intended delta (Δ) configuration, several issues can arise:

Imbalanced voltage and overcurrent conditions

In a delta motor, each winding is connected in a closed-loop triangle configuration. When wired in a star configuration, the connection between the windings changes, resulting in an unbalanced distribution of voltage and current across the motor windings.

Wiring a delta motor in star configuration can cause higher currents to flow through the windings. The lower impedance of the star connection may result in increased current, potentially leading to excessive heat buildup and potential damage to the motor windings or protective devices.

Overcurrent protection mechanisms, such as fuses or circuit breakers, may be tripped due to the increased current.

motor overload relay
4 Amp three phase O.L.R

This can also lead to imbalanced operating voltages between phases resulting in uneven motor performance. The motor may run at a slower speed and experience reduced torque, affecting its overall efficiency and operation.

Power loss and reduced efficiency

Wiring a delta motor in a star configuration reduces the effective voltage applied to each winding. In a star configuration, the phase voltage is √3 (approximately 1.73) times lower than the line voltage. As a result, the available power to the motor is reduced, leading to lower torque output and decreased overall efficiency. This can negatively impact the motor’s performance, particularly when driving heavy loads or operating under demanding conditions.

A delta-connected motor is designed to deliver higher torque compared to a star-connected motor. By wiring the motor in star, the available torque is diminished, which may affect the motor’s ability to drive the connected load effectively. The motor may struggle to start or maintain the required torque, leading to performance issues.

Overheating delta motor

The imbalanced voltages and increased current resulting from a delta motor wired in star configuration can generate excessive heat within the windings, due to the motor trying to compensate for the lower voltage by drawing a higher current to create the torque that’s required.

This can cause overheating of the motor, leading to insulation breakdown, premature component failure, and potentially hazardous conditions.

It is essential to ensure proper motor wiring and adhere to the motor’s intended connection configuration (delta or star) as specified by the manufacturer. Incorrect wiring can have detrimental effects on motor performance, efficiency, and longevity.

Reduced starting capability

The star configuration affects the motor’s starting capability. Compared to the delta configuration, the star connection reduces the starting torque. Even though star configuration is used for starting motors in certain conditions and motor types, this is only done in situations where low starting torque is required by the motor.

This reduction in torque can hinder the motor’s ability to start heavy loads or overcome the initial inertia, potentially resulting in failed starts or inadequate performance.

Wiring a delta motor in a star configuration results in phase voltage and current imbalances, power loss, reduced efficiency, and compromised starting capability. It is essential to ensure that the motor is wired correctly to avoid these issues.

Conclusion

In summary, determining whether a motor is star or delta configuration requires careful examination of the motor’s nameplate or inspection of the terminal connections. The presence of symbols such as Δ (delta) or Y (star) on the nameplate provides clear indications.

Proper identification of the motor’s configuration is essential to ensure correct wiring, efficient operation, and prevent potential damage. When in doubt, consulting the motor’s documentation or seeking assistance from a qualified professional is advisable.

Gavin

I'm Gavin and Iv been teaching electrical science to apprentice electricians in a local technological university since 2022. I hold an Electrical Level 6 QQI Qualification along with several NZEB Certifications.

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