Differences between disconnectors, load switches, switches, and circuit breaker
Different types of devices are available to perform the switching and protection tasks listed in the title which are specially designed to meet the respective requirements. The different parts of IEC 60947 (Low voltage switchgear) specify the design, performance, and test characteristics of the devices.
Differences between disconnectors, load switches, disconnectors, and circuit breakers (in the photo: low voltage disconnector max. 1000A
The most important characteristics of the main types of devices are presented below:
- Disconnectors (disconnectors)
- Load switches
- Switch disconnectors
- Circuit breakers
- Disconnectors (disconnectors)
The disconnector is a mechanical device that in the open position fulfills the requirements specified for the isolation function (IEC 60947-1).
The purpose of the isolation function is to cut off the power supply to all or part of an installation by separating the installation or section from each source of electrical energy for safety reasons.
The key factor here is the opening distance. Insulation must be guaranteed pole to pole and input to input, whether through a visible insulation gap or through appropriate design features inside the device (mechanical locking mechanism).
A device fulfills the isolation function stipulated in IEC 60947-1 when “Free substation isolation at a defined resistance voltage is provided between the open contacts of the main circuit of the switchboard.
It must also be equipped with an indicating device in relation to the position of the movable contacts. This position indicator must be linked in a safe and reliable way to the actuator, the position indicator can also serve as an actuator, provided that it can only display the “Open” position in the “OFF” position, when all the moving contacts are in the “Open” position. This should be verified by testing.
According to IEC 60947-3, an isolator should only be able to make and break a circuit, if a current of negligible size is turned on or off, or if during switching no noticeable voltage difference occurs between the terminals of each pole.
Under normal conditions it can conduct operating currents as well as under abnormal conditions larger currents (e.g. short-circuit currents) for a certain period.
The isolator function can be achieved with various devices, such as for example disconnectors, fused disconnectors, switch-disconnectors, fused disconnectors and circuit breakers with isolation function
4-pole load break switch with visible disconnection and remote trip function (photo credit: directindustry.com)
Load switches (or only “switches”) are mechanical switching devices capable of establishing, withstanding, and breaking currents under normal circuit conditions which may include specified operating overload conditions, as well as currents for a specified time within specified abnormal circuit conditions, such as a short circuit.
A load switch can have short-circuit tap capability, however, it does not have to short-circuit breaking capacity (IEC 60947-1 and -3).
Short-circuit currents can be conducted (high short-circuit resistance capability), but cannot be turned off.
The range of designs of load switches are similar to isolation switches e.g. “normal” (load) switches, fused switches, circuit breakers.
Fuses are not legally permitted in all countries.
Switch-disconnectors; Left – ABB 160-2500A motorized switch disconnector; Right – Schneider Electric low voltage disconnector with free tripping 80-3200A (photo credit: directindustry.com)
Switch disconnectors combine the properties of (load) switches and disconnections. Also in this case there are a variety of models such as “normal” switch-disconnectors, fused switch-disconnectors, and circuit breakers.
Fuse-switch-disconnectors are not legally authorized in all countries.
Schneider Electric Low Voltage Molded Case Circuit Breaker (MCCB) Compact NSX Type
Circuit breakers are mechanical switching devices capable of making, withstanding and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short circuit (IEC 60947-2)
They therefore also meet the requirements of (load) switches. Circuit breakers are often designed so that they can meet the requirements of disconnections.
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