Views: 0 Author: Luna Publish Time: 2026-08-10 Origin: Zhejiang Shengxian Electric Technology Co., Ltd
In power distribution, one wrong operation can destroy equipment or cause fatal injuries. That‘s why medium and high voltage switchgear must include a “Five-Prevention“ interlocking system.
This article explains what it is and why it matters.
It is a set of five safety functions designed to prevent operator errors:
No. | Prevention |
|---|---|
1 | Prevent incorrect opening/closing of the circuit breaker |
2 | Prevent opening/closing the disconnector under load |
3 | Prevent closing the earthing switch while the circuit is live |
4 | Prevent closing the breaker while the earthing switch is closed |
5 | Prevent entry into live compartments |
Prevention 1: Wrong breaker operation = unnecessary outage or damaged equipment.
Prevention 2: Disconnectors cannot break load current — operating under load causes arcing and short circuits.
Prevention 3: Earthing a live circuit equals a direct short to ground — severe damage.
Prevention 4: Closing a breaker with earthing still applied = power source directly grounded — explosion risk.
Prevention 5: Opening a live compartment door = deadly electric shock risk for personnel.
Through interlocking devices:
Type | How It Works |
|---|---|
Mechanical | Physical locks force the correct sequence — reliable and durable |
Electrical | Circuits prevent operation unless conditions are met — used as backup |
Most switchgear uses mechanical interlocking as the primary method, with electrical interlocking as additional protection.
Reason | Why |
|---|---|
Safety | Prevents electric shock and injury to operators |
Equipment protection | Stops costly damage from short circuits |
Compliance | Required by IEC 62271-200 and GB 3906 standards |
The “Five-Prevention“ system is the minimum safety requirement for switchgear.
When purchasing, always check that the unit has a complete mechanical interlocking system.
Questions?
Contact us.
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WhatsApp: +195 1818 9858
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