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maximum short-circuit current

Molded Case Circuit Breaker (MCCB)—rated current up to 2,500 A. Thermal or thermal-magnetic operation. Miniature circuit breaker (MCB)—rated current not more than 100 A. Trip characteristics normally not adjustable. In the United States, Underwriters Laboratories (UL) certifies equipment ratings, called Series Ratings (or “integrated equipment ratings”) for circuit breaker equipment used for buildings.

The circuit breaker is labeled with the rated current in amperes , but excluding the unit symbol, A. VS1-12 type indoor high voltage vacuum circuit breaker is preceded by a letter, B, C, or D, which indicates the instantaneous tripping current — that is, the minimum value of current that causes the circuit breaker to trip without intentional time delay (i.e., in less than 100 ms), expressed in terms of In: Circuit breakers are manufactured in standard sizes, using a system of preferred numbers to cover a range of ratings. Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker’s interrupting capacity rating may result in failure of the breaker to safely interrupt a fault.

The maximum short-circuit current that a breaker can interrupt is determined by testing. When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. This arc must be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit.

The length of the arc is generally proportional to the voltage while the intensity (or heat) is proportional to the current. When a high current or voltage is interrupted, an arc is generated. Small circuit breakers typically have a manual control lever to switch off the load or reset a tripped breaker, while larger units use solenoids to trip the mechanism, and electric motors to restore energy to the springs.

Simple air-break manual switches produced hazardous arcs when interrupting high voltages; these gave way to oil-enclosed contacts, and various forms using the directed flow of pressurized air, or of pressurized oil, to cool and interrupt the arc. Is ZW20-12 type vacuum circuit breaker of the improvement of products. Hereinafter called combination intelligent circuit breakers) according to customer’ s requirement.

With 2 primary coils, this current transformer offers 2 current ratios while maintaining the required accuracy and burden rating at each current ratio. The AWF Series current transformers are available in various classes of accuracy (0.15S, 0.15, 0.2S, 0.2, and 0.3) and have a burden rating of B-0.5. In addition, they can be offered as Extended Range Current Transformers (ERCT) if requested by the customer. Accuracy 0.15S~0.3; burden B-0.5. Available as Extended Range Current Transformers (ERCTs) if requested.

Used for power monitoring or as part of an MOF (Metering Outfit) for a 12~36kV power system, these outdoor CTs for billing are insulated with Araldite® UV-resistant cycloaliphatic epoxy. CIC specializes in the manufacture of instrument transformers, distribution transformers, detuned reactors, epoxy insulators, electronic energy meters, etc. More than 15 cellular indoor substations have been designed.

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