12 Leads. If leads are numbered 1 to 12, the motor is typically rated for two voltages and could be used with a wye-delta starter at either voltage, or a part-winding starter for low voltage only. Twelve-lead induction motors will almost always run connected delta.

1. Turn off the power supply to the motor, usually accomplished by switching the circuit breaker.
2. Place one megger probe to the any mounting bolt on the breaker box to test for grounding continuity, then touch the other probe to a motor terminal.
3. Crank the handle for about a minute, and notice the resistance reading.

Some dual-voltage, three-phase AC induction motors are available with twelve leads instead of nine. Usually, a 12-lead motor is required for reduced-torque wye-to-delta starting methods.

This type of motor is probably the most commonly used in factories, lumber-mills, and other commercial plants. They are dual-voltage and can be wired for either 240VAC or 480VAC. Each motor will have 9 numbered leads coming out of the motor. The leads are numbered to aid the electrician when connecting the motor.

Three phase motors on a three phase three wire system only need two line and motor leads interchanged to reverse the motor rotation. A polarity change of one phase in relation to the other two in a typical three phase generator feed system that is functioning properly is impossible.

If leads are numbered 1-6, the winding can usually be connected wye or delta. On machines rated for two voltages, the wye connection is for the high voltage; the delta connection is for the low voltage.

An advantage of the Delta connection is higher reliability. If one of the three primary windings fails, the secondary will still produce full voltage on all three phases. An advantage of the Wye connection is that it can provide multiple voltages without the need for additional transformers.

First, you can check the motor nameplate data which is usually located on a paper or metal label attached to the side of the motor. Second you can simply look at the number of electrical leads coming out of the motor. If your motor has three black leads and a green lead then it is likely three phase.

If the motor is left connected in Star, it will run at the correct speed, but it will have 1/3 less power than when Delta connected.

when you connect the delta connection motor into a star connection mode, the effective per phase voltage is reduced to (1/1.732) times hence to maintain the torque/speed it will draw 1.732 times higher current.

If Star connection has sufficient torque to run up to 75% or %80 of full load speed, then the motor can be connected in Delta mode.

The delta connection in a motor is used because it provides more power and starting torque. The star connection is used where you may want to reduce the starting current of a motor to get it up to speed and then connect in delta for normal running mode.

Obviously In Power Transformers Primary winding is Delta connection and Secondary is Star. In delta connection line voltage is equal to phase voltage. That means there is no difference between line and phase voltages so therefore what is the use of neutral in delta connection.

Star connected motors have a central connected point, called a short circuit point or star point and each winding receives phase voltages (230volts), star connected motor only run at one third of the motor rated torque and power, whereas delta connected motors have no connected point and each winding receives line …

In Star Connection, Phase voltage is low as 1/√3 times of the line voltage, whereas in Delta Connection Phase voltage is equal to the line voltage.

In potential transformer the primary and secondary windings are star connected, because in star configuration, the line voltage is root 3 times of phase voltage, hence the voltage distribution to each winding is reduced or divided by 1.732 times. Due to that the insulation cost on the primary winding comes lesser.

Alternators are connected primarily in star to achieve the following motives: Lesser stress on insulation and Copper saving: Voltage per phase is less for a given line voltage which reduces insulation requirement and this also reduces the number of turns hence copper is also saved.

Transformers for high voltage operation with the star connections has the advantage of reducing the voltage on an individual transformer, reducing the number of turns required and an increase in the size of the conductors, making the coil windings easier and cheaper to insulate than delta transformers.

The power of all three phases can be transmitted on three conductors. This connection is called a star, or wye, connection. Alternatively, since the three winding voltages also sum to zero at every instant, the three windings can be connected in series—a′ to b, b′ to c, and c′ to a—to form a delta connection.

Neutral grounding of generators is used to protect the generator and associated equipment against damage caused by abnormal electrical conditions, in order to: Minimizing damage to the stator core caused by internal ground faults. Providing a sensitive means of ground fault detection.

Bonded Neutral Generator The safety standards of the NEC article 250 require that the neutral must be grounded at the first means of disconnect (which means the nearest possible point), and cannot be grounded twice, to avoid induced transient voltages or currents.

If the alternator is not grounded the circuit cannot be completed to allow it to work properly. I’ve seen headlights grounded to newly painted radiator supports that the electrical connection between the radiator support and the rest of the car is very poor or non existant.

5.0 ohms

The value of earth resistance will increase when length of earth pipe is increased. Explanation: Earth resistance is the resistance between the electrode and point of zero potential.

An alternating current (I) is passed through the outer electrode C and the voltage is measured, by means of an inner electrode P, at some intermediary point between them. The Earth Resistance is simply calculated using Ohm’s Law: Rg = V/I.

Another way to lower earth resistivity is to treat the soil with a salt, such as copper sulfate, magnesium sulfate, or sodium chloride. Combined with moisture, the salts leach into the soil to reduce earth resistivity.

2.5 meters

Factors affecting on Earth resistivity

• Soil Resistivity. It is the resistance of soil to the passage of electric current.
• Soil Condition.
• Moisture.
• Dissolved salts.
• Climate Condition.
• Physical Composition.
• Location of Earth Pit.
• Effect of grain size and its distribution.

One of the simplest grounding problems to fix is making sure that all ground connections are correct.

1. Shut off the main electrical power.
2. Find the grounding rod driven into the ground.
3. Check the ground connection clamp.
4. Check the ground wire running to the copper or galvanized water service inside the house.