What are the mandatory tests for low-voltage switchgear before it leaves the factory?

The mandatory tests for low-voltage switchgear before it leaves the factory mainly include factory tests to ensure that each piece of equipment meets safety and performance standards before delivery. These tests are the final quality control checkpoint and directly affect the reliability of the equipment in actual operation.

 

1. Power Frequency Withstand Voltage Test

Purpose: To verify the insulation strength of the main circuit and auxiliary circuit.

Standard: Apply a voltage of (2U + 1000) × 1.5 (U is the rated voltage), with a minimum of 2250V; maintain for 1 minute without breakdown or flashover.

Operating Points: Gradually increase the voltage from 30% to 50% to the specified value, maintain for 1 second, and then slowly decrease it to zero.

 

2. Insulation Resistance Test
Use a 500V megohmmeter to measure the insulation resistance of the main circuit to ground and between phases. The insulation resistance should be ≥1MΩ to ensure that there will be no accidents caused by leakage during long-term operation.

 

3. Protection Circuit Continuity Check:

Measure the DC resistance between the frame, door panel, and protective grounding busbar. The resistance should not exceed 0.01Ω.

If the door panel has a powder coating or paint layer, remove the coating at the connection points to ensure good conductivity.

 

4. Mechanical Operation and Functional Unit Interchangeability Test:

Perform multiple opening and closing operations on circuit breakers, disconnect switches, and drawer units to ensure smooth and unobstructed operation.

Removable functional units (such as drawer cabinets) require interchangeability testing. Units of the same specifications should be reliably interchangeable and operate normally.

 

5. Electrical Clearance and Creepage Distance Verification:

Although not a dynamic test, these are critical parameters that must be verified before shipment: Distance between exposed conductors of different polarities ≥ 20mm; creepage distance ≥ 12.5mm.