The difference between PC class and CB class in automatic transfer switch and key points of selection

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The difference between PC class and CB class in automatic transfer switch and key points of selection
11 15 , 2021
Category:Application

Dual power Automatic switching switch referred to as ATSE, Automatic Transfer switching equipment, commonly known as dual power switching. As the name implies, it is automatically connected to the standby power supply through the double power switch when the power is suddenly cut off, so that our operation will not stop, still can continue to operate.

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The purpose of the dual power automatic transfer switch is simply to use one common way and standby way. When the common power suddenly fails or fails, the dual power switch is automatically put into the standby power supply (the standby power supply can also be powered by the generator under small load) so that the equipment can still run normally. Most commonly used are elevators, fire protection, surveillance, and the bank’s UPS uninterruptible power supply, but his backup is a battery pack.

This switching appliance useful to the place there are many, is very important to ensure the reliability of double power supply, electrical friends must know how to correctly choose and distinguish.

01, dual power supply automatic switch PC level and CB level difference

PC class: Isolated type, like double knife throw switch, with operating mechanism, can on and carry normal and fault current, but not to break short circuit current. Power supply continuity can be maintained when the load is overloaded. Fast action time. Contact for silver alloy, contact separation speed, a specially designed arc chamber. Small size, only half of CB class.

Application: manual – used for communication base station, power plant AC/DC split screen; Electric – for diesel generators; Automatic – used for power distribution, lighting, fire protection and other situations in construction projects.

Plotting symbol (PC level)
截图20211115130500
CB class: CB class adopts circuit breaker as the actuator, based on two circuit breakers, controlled by the controller with mechanical interlocking electric transmission mechanism to realize the automatic conversion of two power supplies, switching time 1-2s. Equipped with overcurrent tripping device, its main contact can be switched on and used to break short circuit current. It has overload protection function for load side electrical equipment and cable, can connect, carry and break short circuit current, when the load appears overload or short circuit, disconnect the load.

Application: used for building power distribution, lighting, fire protection and other non-important load occasions; Used in industrial markets (such as metallurgy, petrochemical, power plant, etc.), high-speed rail and railway projects and other occasions; It can also be used with a master couplet.

Plotting symbol (CB level)
截图20211115130521

02, double power supply automatic switch selection points

1) From the perspective of reliability, PC level has higher reliability than CB level. PC level uses mechanical + electronic conversion action lock, while CB level uses electronic conversion action lock.
So far, the CB class dual power automatic switch in the world is composed of two circuit breakers, which is the most complex structure of all kinds of dual power automatic switch solutions (the moving parts are more than twice as many as the PC class dual power automatic switch). The reliability of CB class dual power automatic switch is lower than that of PC class dual power automatic switch (for the same reason that the reliability of circuit breaker is lower than that of load switch).

2)  Action time the action time difference between the two is large, for evacuation lighting and other loads, basically can only use PC level, because the required switching time is too short.

3)The PC-level dual power switch has no short-circuit protection function, so whether to add additional circuit breakers should be considered according to the needs of the circuit system. Over-load power will cause serious consequences of the line, its over-load protection should not cut off the line, can act on the signal. When class CB ATses are used to supply power to fire fighting loads, atses consisting of circuit breakers with only short circuit protection shall be used. So in order to save trouble, fire load is generally used PC level. Dual power switch its role is to achieve dual power conversion function, there is no short-circuit protection function will not affect its operation. Many people think that the short circuit function is used to protect the switch, which is a misunderstanding.

4) Whether to set the isolation switch Installing the isolation switch will occupy space, increase cost and reduce reliability. It is recommended that the number of isolation switches installed in the industrial power system should be controlled, and it is not necessary to set the isolation switch in the residential floor.

5)PC class: can withstand the expected short-circuit current, rated current is not less than 125% of the calculated current. Class CB: When class CB ATses are used to supply power to fire fighting loads, atses consisting of circuit breakers with only short circuit protection shall be used. The CB class dual power automatic switch is actually a circuit breaker. Set CB class dual power automatic switch parameters according to the principles and methods for selecting circuit breakers. If you choose a brand, verify that the circuit breakers used by the brand meet the requirements of the installation position. Based on the above reasons, it is recommended to select MCCB with only short-circuit protection function as the body switch of class CB dual-power automatic switch. This point is often ignored, most designers choose CB class dual power automatic switch, only mark the product model, current grade and series, ignoring the type of circuit breaker used, specifications, etc..

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