Disconnecting Switch with Earth (Earthing Switch): A Critical Safety Component
A Disconnecting Switch with Earth—its formal names are Earthing Switch or Grounding Switch—is a safety device you can’t do without. It’s used in medium and high-voltage electrical systems, usually 1 kV AC and above. Its main job, which is all about safety, is to connect the isolated, power-off parts of an electrical circuit to earth reliably.
Let’s talk about what it does and why it matters. First, it keeps things safe by grounding. When a circuit is opened (isolated) by its matching disconnector—people also call that an isolator—and checked to have no power, you close the earthing switch. This makes a path to earth that doesn’t block electricity much. Then, it protects people. This connection makes sure any accidental power-on—like from switching mistakes, back-feeds, or induced voltages—or leftover charge flows safely to earth. That’s key for people working on downstream equipment, things like circuit breakers, transformers, or busbars. It stops dangerous voltage from showing up on the isolated part, so they don’t get a deadly electric shock. It also acts as a discharge path. After the system is turned off, it gives a controlled way for capacitive energy to escape. That energy is stored in long cables, bushings, or other system parts.
There are important things about how it’s designed and works. Mechanical interlocking is one. Earthing switches always have mechanical links with their matching disconnector. This is basic: the disconnector must be fully open before you can close the earthing switch. And the other way around—the earthing switch must be fully open before you can close the disconnector. This stops you from closing the earthing switch onto parts that still have power. Electrical interlocking is common too. Control circuits often add these to boost safety. They stop you from operating the switch remotely or locally unless it’s safe. It also has a short-time current rating. Earthing switches can carry and handle certain short-circuit currents for a short time—usually 1 or 3 seconds. This means they can handle fault currents safely if you accidentally close them onto a live system (even with interlocks) or if a fault happens on the earthed part. They work until the main circuit breaker fixes the fault. They have making capacity too—this is the highest current they can close onto safely, like if you accidentally close them onto a live circuit without damage. And you need clear visual signs to show if the switch is open or closed.
Earthing switches follow strict international standards for design, testing, and type-testing. The main one is IEC 62271-102, for AC disconnectors and earthing switches. They’re key parts of switchgear like Gas-Insulated Switchgear (GIS) and Air-Insulated Substations (AIS). You’ll find them on both sides of circuit breakers and on feeder circuits.
To sum up, the Abimat earthing switch isn’t an isolation device. But it’s a vital safety tool. Its only job is to keep an isolated circuit part reliably and safely connected to earth. This protects people from electric shock during maintenance and commissioning. Strong mechanical and electrical interlocks make sure it works reliably—this is a must for safe high-voltage system operation.
