Surge arrester is also called over-votage protector and over-volage lmiter. t is connected im paralle to the front end of the protected couipmen,. Whichprolects other clectrical equipment from lightning over-voltage, operating over-voltage, and power frequency transient over-voltage impac. Composite Arrester,Electrical Insulation Composites,Electrical Box Insulation Covers,Composite Line Post Insulator Jilin Nengxing Electrical Equipment Co. Ltd. , https://www.nengxingelectric.com
Circuit breaker safe load current calculation formula - Database & Sql Blog Articles
Circuit breakers are the most fundamental electrical protection components and are widely used, with a significant social reserve. They have become the most important, commonly used, and essential protective device in modern life and industry. Ensuring that the circuit breaker can reliably protect the circuit and safeguard the load is crucial. However, for a long time, there has been no precise safety data or calculation formula for the load current of a circuit breaker. The national standard GB14048.2 outlines the rated current inspection criteria for circuit breakers. Determining whether the load current falls within the safe protection range of the circuit breaker is a complex calculation problem for professionals and a major challenge for non-experts.
This lack of clear guidelines often leads to improper selection of the circuit breaker’s rated current. Many engineers or technicians choose the rated current based on the expected maximum load or the short-circuit breaking capacity, sometimes even increasing it unnecessarily to avoid tripping. This results in situations where the circuit breaker fails to provide proper protection, leaving the circuit and load vulnerable to overloads or short circuits, which can cause serious accidents, fires, and even injuries or fatalities.
The absence of an exact formula for calculating the safe load current of a circuit breaker has led many to believe that simply installing a circuit breaker ensures the safety of the line and load. Even some professionals hold this misconception, leading to incorrect selections and the loss of critical protection functions. To address this issue, after years of practical experience and analysis, along with references to both national and international standards (GB14048.2 and IEC 60947-2), a set of formulas for calculating the safe load current of a circuit breaker has been developed.
For inverse time overload protection, the standard specifies that the non-operating current is 1.05 times the rated current, while the operating current is 1.3 times. Using these values, the minimum limit load current can be calculated as IL > 0.81 × Ir. This means that if the load’s rated current is below 81% of the circuit breaker’s rated current, the circuit breaker may not offer adequate overload protection.
Similarly, for time-delayed short-circuit protection, the formula shows that the minimum load current should be greater than 67% of the circuit breaker’s rated current. If the load’s rated current is lower than this threshold, the circuit breaker will not trip during a short circuit, posing a serious risk.
By applying these formulas, the circuit breaker can be properly sized to ensure that the load remains within the safe protection range. This helps prevent dangerous situations and ensures that the circuit breaker functions effectively, providing real protection rather than just switching power.