Sequence of closing and opening the switch in the distribution box

The correct sequence ensures safety and proper energization: open LV first, then HV; close in reverse order, always avoiding operating isolating switches under load.

Power-Off Sequence (De-energizing)

1. Low-Voltage (LV) Side First: Open all LV branch circuit breakers, then the LV main breaker. Disconnect control circuits before main power circuits. Open the circuit breaker first, then the isolating switch (disconnector) if present .
2. High-Voltage (HV) Side: Open HV outgoing isolating switches, then HV outgoing circuit breakers. For incoming HV lines with two isolating switches, open the load-side switch first, then the source-side switch .
3. Safety Measures: Ensure all personnel are clear, remove temporary grounding wires (disconnect line end first, then grounding end), and verify that all equipment is de-energized .

Power-On Sequence (Energizing)

1. Preparation: Confirm no personnel are working on equipment, remove grounding wires and warning signs, and verify incoming line switches are open .
2. Bus-Tie and HV Switches: Close the bus-tie isolating switch between HV busbars to operate in parallel. Sequentially close all isolating switches on the incoming line, then close the incoming circuit breaker. Verify busbar integrity .
3. Voltage Transformers and Outgoing Circuits: Close isolating switches for voltage transformer circuits, then all HV outgoing isolating switches, followed by HV outgoing circuit breakers to energize main transformers .
4. LV Side: Close the LV knife switch of the main transformer, then the LV circuit breaker. Verify LV busbar voltage using voltmeters. Close all LV outgoing knife switches, then LV circuit breakers or fuse-switch disconnectors to energize all LV circuits .

Restoring Power After Faults

• If a circuit breaker trips due to a short-circuit, reclose the breaker after the fault is cleared. The procedure may vary depending on the type of switchgear installed .
• For automatic reclosing (AR) sequences, the breaker may close after a short delay (0.2–180 s depending on settings) to ensure the fault is cleared before energizing the circuit again .

Key Safety Notes

• Never operate an isolating switch under load.
• Always follow the sequence: LV first when opening, HV first when closing.
• Verify all voltages and busbar integrity before energizing downstream circuits.
• Use proper interlocks and control schemes to prevent closing onto a fault .

Following this sequence ensures safe operation, prevents equipment damage, and maintains system reliability in distribution rooms.