difference between upper and lower grounding switches
The fundamental difference between upper and lower grounding switches lies in their installation location and the object they ground, which directly determines their function and safety level.
Current path in switchgear: Power supply (upper) → Switching equipment → Load (lower).
I. Upper Grounding Switch
1. Definition and Location
An upper grounding switch is installed upstream (on the power supply side) of the main circuit of the switchgear. It is usually located above the disconnecting switch and directly connected to the busbar system.
2. Grounding Object and Function
Grounding Object: Its main grounding object is the busbar. The busbar is the main conductor that runs through a row of switchgear, used for collecting and distributing electrical energy.
Core Function: When this section of the busbar needs to be de-energized for maintenance, the upper grounding switch is closed, reliably grounding the busbar.
3. Safety Protection Scope
It mainly protects the safety of personnel working inside the switchgear, especially in the busbar room. When the upper grounding switch is closed, it means that the entire section of the busbar above this switchgear is grounded.
Highest safety level: Because it relates to the safety of the entire busbar, its interlocking logic is also the most stringent, preventing energized closing.
II. Lower Grounding Switch
1. Definition and Location
The lower grounding switch is installed downstream (load side) of the main circuit of the switchgear. It is usually located below the circuit breaker and current transformer, directly connected to the outgoing cable.
2. Grounding Object and Function
Grounding Object: Its main grounding object is the outgoing cable and downstream line.
Core Function: When the outgoing cable or downstream equipment connected to this switchgear needs maintenance, the lower and upper grounding switches are closed.
3. Safety Protection Scope
It mainly protects the safety of personnel working outside the switchgear, on the outgoing cable, or on downstream equipment. It is equivalent to providing a set of "visible" safety grounding wires for line workers.
Wide Application: This is a standard configuration for outgoing switchgear. Almost every outgoing switchgear used to control a single line is equipped with a lower grounding switch.
