Quality inspection of molded case circuit breakers: strict control to ensure safety

The quality inspection of molded case circuit breakers is crucial. The following is a specific introduction:

###Testing items
-* * Mechanical performance testing * *:
-Overtravel test: Overtravel refers to the distance that the stationary contact moves away and the moving contact continues to move forward after the contact is closed. Testing overtravel is to ensure that the product can maintain normal power supply in case of wear during use. Open distance refers to the shortest distance between the moving and stationary contacts of a circuit breaker after it is disconnected. Testing it is to ensure that the product can quickly disconnect and cut off the fault arc in the event of a short circuit.
-* * Mechanical running in synchronization release force test * *: The product is mechanically run in by opening and closing the switch, measuring the contact synchronization, release force, and release stroke to ensure that the relevant mechanical characteristics of the product are more stable.

-Circuit resistance final pressure test: The resistance of the conductive circuit of a circuit breaker mainly depends on the contact resistance between the moving and stationary contacts of the circuit breaker. Appropriate final pressure can suppress the abnormal bouncing of the moving and stationary contacts when closing, in order to maintain reliable contact between the moving and stationary contacts. Increasing the final pressure can reduce the contact resistance and thus lower the temperature rise of the circuit breaker.
-Electrical performance testing:
-Instantaneous action characteristic test: Conduct a full inspection of the instantaneous protection function of the circuit breaker to ensure the reliability and safety of its performance during opening and closing, and to ensure that the circuit breaker can reliably disconnect in the event of a short circuit in the circuit.
-Delay Test: Testing the overload protection function of circuit breakers. By setting the delay characteristics reasonably, it is possible to avoid damage to electrical circuits or accelerate circuit aging due to overload, thereby ensuring the safe operation of the entire electrical system.

-* * Voltage resistant sliding buckle test * *: Sliding buckle test refers to the detection of the normal on-off status of the product during the opening and closing process. Voltage withstand test refers to the inspection of the dielectric performance of products by testing the phase to phase, handle to ground, and incoming and outgoing line ends, checking the installation quality of circuit breakers, and assessing the insulation strength of circuit breakers.
-* * Logo and appearance inspection * *: Check whether the product logo is clear and complete, including the model, specifications, rated voltage, rated current, breaking capacity and other parameters are complete and meet the standard requirements. Visually inspect the circuit breaker casing for cracks, damage, deformation, uniform surface color, and whether the wiring terminals are yellow, gray, or even burnt. If there is burnt, it is usually due to poor contact or damage.

###Testing standards
The quality inspection of molded case circuit breakers is usually carried out in accordance with national standards such as GB/T 14048.2-2020 "Low voltage switchgear and control equipment Part 2: Circuit breakers", and some enterprises may also implement stricter enterprise standards.

###Testing method
-* * Professional equipment testing * *: high-precision sensors, measuring instruments, etc. are used to accurately measure various parameters, such as the sensor sampling range of 5-60mm, resolution of 0.05mm, and accuracy of ± 2% used in overtravel distance testing; The current output accuracy used in the instantaneous action characteristic test is ≤± 3%, and the accuracy of the current transformer is 0.2 level.
-Sampling testing: In the production and circulation fields, samples are selected for testing according to a certain sampling method to represent the quality status of the entire batch of products. According to the regulations of Yueqing City, for products in the production field that explicitly implement the standard GB/T 14048.2-2020, 4 samples are taken from each batch, of which 2 are used as inspection samples and 2 are used as backup samples; Three samples are taken from each batch in the circulation field, of which two are used as inspection samples and one is used as a backup sample.

###The Importance of Testing
-* * Ensuring electrical safety * *: Molded case circuit breakers are often used as terminal switches or branch switches in low-voltage distribution systems. Once quality problems occur, if the fault current cannot be cut off in a timely manner, it may cause serious safety accidents such as electrical fires, equipment damage, and even personal injury.
-Improving product reliability: Through strict quality testing, defects and problems in the design and manufacturing process of products can be discovered in a timely manner, prompting enterprises to continuously improve production processes and product quality, enhance product reliability and stability, and reduce the occurrence of failures.
-Maintaining Market Order: Conducting quality inspections on molded case circuit breakers can prevent unqualified products from entering the market, protect the legitimate rights and interests of consumers, maintain normal market order, and promote the healthy development of the entire industry.