Trace An Earth Leakage Fault Full GFP Setting

When current is pushed through each CT, the half trip has an additive effect, resulting in double the secondary current, instead of canceling out like in the no trip test.

This is possible because the system has sufficient voltage to maintain an arc between one phase and ground, but not enough current to operate a main breaker or fuse.

Ground fault protection is required by the NEC and is usually installed only on circuits and services of 480277 volts, 1,000 amps and larger.

When a ground fault occurs in an electrical system, energized components make contact with grounded components, resulting in current flow through the grounding conductors.

There are two main current transformer arrangements used for this system.

If there is an imbalance in the signals, a secondary current will be produced that is used to activate the ground fault relay.

If current flows through the ground conductor, it will not pass through the CT, resulting in an imbalance.

If one element is incorrectly wired, inoperative, not calibrated, or damaged, the ground fault protection may not operate.

This testing shall be conducted by a qualified person(s) using a test process of primary current injection, in accordance with instructions that shall be provided with the equipment.

A written record of this testing shall be made and shall be available to the authority having jurisdiction.

Particularly in the tests requiring the use of a high-current test set, it is usually necessary to obtain the services of a qualified field testing organization.

Trace An Earth Leakage Fault Full GFP Setting

If inspection authorities require tests at full GFP setting, a current supply capable of delivering 1200 amperes or more may be needed.

One of the most important checks is visual, making sure that only the correct number of phase and neutral conductors pass through the zero-sequence current sensor in the proper direction.

Main breaker should not trip when test current exceeds the predefined pickup and time delay setting.

Main breaker should trip when test current exceeds the predefined pickup and time delay setting.

If the required current cannot be achieved, the test lead can be wrapped around the sensor one or more times to multiply the secondary current produced by the sensor.

This is required to provide a low-impedance ground fault current return path to the neutral to assure operation of the overcurrent device.

Once neutral and ground resistance is verified, re-connect the bonding jumper before proceeding with high current testing.

The no trip test is wired to simulate normal load conditions, traveling through a phase sensor and back through the neutral sensor in the correct direction.

Because the two current transformers cancel each other out, no trip is expected from the ground fault relay.

Current should be raised and held above the pre-defined pickup setting for a duration longer than the predefined time delay.

Its called the half trip test because it requires one-half the current required to perform a normal trip test.

How To Trace An Earth Leakage Fault