This article is about inspection and testing method statement of electrical system used in commercial buildings, plants and petrochemical refineries.
Electrical System Inspection and Testing
Inspection:
Material and Workmanship Inspection: Field representative Engineer have the authority to inspect materials and workmanship at any location where fabrication and erection are taking place. If any defective material or workmanship is identified, it must be rectified to the satisfaction of the field representative.
Notification for Testing: Before conducting any required testing, a minimum notice of 24 hours must be given to the field representative.
Testing:
Engineering Contractor Responsibility: The contractor is responsible for providing all necessary labor, materials, and equipment to perform the tests outlined in this section. The specific requirements for each test are indicated by unique codes.
Requirement for Electrical Test:
| A | All electrical testing documentation shall show the full nameplate data of the equipment and, if applicable, the load test current for each phase (in addition to other required test data). |
| B | The tests must be witnessed by a qualified field representative possessing a technical understanding of the tests being performed and the test equipment being used. |
| C | The tests shall be performed by a reputable and qualified specialized testing service approved by the field representative and, where applicable, the inspection agency having jurisdiction. |
| D | The test equipment used shall be calibrated and certified and shall be according to the calibration requirements specified in General Scope of Work for Construction Contract. Documented evidence of calibration shall be provided to the representative. Documented evidence of calibration shall include: 1. Identification of the equipment being calibrated. 2. A reference to the procedure used for calibration. 3. Equipment used to perform calibration. 4. Check method Statement. 5. Calibration date. 6. Individual performing calibration. 7. Calibration due date. |
Insulation Resistance Test Values for Electrical Apparatus and Systems
This table is From NETA ATS-2013 (Table 100.1)
| Nominal Rating of Equipment in Volts | Minimum Test Voltage, DC | Recommended Minimum Insulation Resistance in Megohms |
| 250 | 500 | 25 |
| 600 | 1,000 | 100 |
| 1,000 | 1,000 | 100 |
| 2,500 | 1,000 | 500 |
| 5,000 | 2,500 | 1,000 |
| 8,000 | 2,500 | 2,000 |
| 15,000 | 2,500 | 5,000 |
| 25,000 | 5,000 | 20,000 |
| 34,500 and above | 15,000 | 100,000 |
Test results are dependent on the temperature of the insulating material and the humidity of the surrounding environment at the time of the test.
Electrical System Testing List:
| 1 | Wiring and Terminations. All wiring shall be tested and inspected to ensure wire is connected to the right terminals, free of short circuits, and of proper continuity. All terminations shall be checked and inspected for loose connections in lugs or terminals. | A |
| 2 | Test each oil-filled transformer or circuit breaker as follows: See specifications [Electrical & Mechanical Inspection for Equipment (Oil, Vacuum, Gas Circuit Breakers)] and [Liquid Filled Transformer: Testing and Commissioning] for additional tasks to be completed by the electrical contractor. If oil is to be added to any unit, fill by means of a closed loop filter press process. Dielectric test an oil sample from each drum of new oil before using, and dielectric test unit oil before and after the filling process. | A, B, C, D |
| 3 | Test each vacuum and gas circuit breaker. See technical specification [Commissioning: Substation, High-Voltage, Oil/Vacuum/Gas Circuit Breakers] for tasks to be completed by the electrical contractor. | A, B, C, D |
| 4 | Motors: For additional tasks assigned to the electrical contractor, please refer to specification 4AEL-620106. Before making connections, ensure the accuracy of motor lead markings by conducting a continuity check using a volt ohmmeter. Proceed with the connection of the motor stator and any other associated space heaters. Finally, conduct a load check and record the current in amps: ___________. | A, B | ||
| 5 | Grounding Electrode System Measure the resistance of all accessible grounding electrode system pigtails and document the results on the Grounding Electrode Conductor Resistance Results form (Form 2). Tests shall be performed using a clamp-on ground resistance tester AEMC Instruments 3711 or equal. Measurements shall be made with grounding electrode pigtail connected to equipment. Any reading above the maximum resistance values identified in the following list shall be brought to the immediate attention of the field representative. See specification 4AEL-620112 for additional tasks to be completed by the electrical contractor. | A, B, D | ||
| Item | Maximum Resistance (ohms) | |||
| Iso-ground Reference Plate (where applicable) | .05 | |||
| Switchgear/E2 Starter Ground Bus | .05 | |||
| Motor Control Center Ground Bus | .05 | |||
| Ground Resistor Ground Connection | .05 | |||
| Substation Equipment Frames | .05 | |||
| High-Voltage Transformer Frames | .25 | |||
| Electric Yard Support Structures | .25 | |||
| Electric Yard Fence | .25 | |||
| Moore Products DCS cabinet | .50 | |||
| Switchgear/E2 Starter Frame | .50 | |||
| Motor Control Center Frame | .50 | |||
| Distribution Transformer Frames | .50 | |||
| Distribution Panel Frames | .50 | |||
| High-Voltage Motor Ground Buses | 1.00 | |||
| 6 | After completion of the electrical installation, the contractor and the field representative shall visually inspect and ensure that all of the grounding electrode system pigtails have been connected as identified on the contract drawings. All exothermic connections shall be strength tested by tapping the weld with a one-pound hammer. | B | ||
| 7 | Perform dc insulation resistance test on all 480-volt feeders before connection to the equipment and document the results on the Insulation Resistance Test form (Form 1). | A, D | ||
| 8 | Perform dc insulation resistance test on all 480-volt motors complete with leads to the starter before the initial energization for a rotation check. One megohm after one minute is acceptable. Remove leads at the starter, VFD or soft start before the test. Never Hi-pot motor windings. | A, B, D | ||
| 9 | All 3-phase, 480-volt heaters shall be checked to ground with a volt ohmmeter before energization. If resistance is less than 20,000 ohms, a reduced voltage shall be applied to the unit as required to dry the insulation. Full voltage shall be applied for 30 seconds per hour maximum (unless otherwise directed by the field representative) and the load on each phase shall be measured. | A | ||
| 10 | All motor, heater, and process control circuits shall be energized and functionally checked without energizing the unit (use breaker test position, remove motor overloads, and disconnect leads, as required). The correct operation of each start, stop, bypass, interlock, and alarm device in the circuit shall be demonstrated. | A, B | ||
| 11 | All welding outlets shall be demonstrated for consistent phase rotation, proper voltage, and grounding. Outlet shall also be visually inspected to verify outlet meets manufacturer’s catalog number according to contract drawings or electrical symbols. | B | ||
| 12 | All 120V receptacles shall be checked for the correct wiring with a standard three-lamp tester. GFCI-protected receptacles shall be tested with a GFCI tester. GFCI receptacles and breakers shall be tested with integral test and reset buttons. | B | ||
| 13 | Perform dc insulation resistance test on each bus duct section before assembly. Re-test as each section is added during assembly. Perform final test on the completed bus duct and perform a contact resistance test. Contact resistance test values shall be 30 micro-ohms per joint, or less. All transformer testing shall be completed before making final bus duct connections to transformer. | A, B, D | ||
Form 1 – Insulation Resistance Test Results:
Form 2 – Grounding Electrode Conductor Resistance Test Results
