dc islators 1

DC isolating switch



The main purpose and components of an isolating switch

The primary function of an isolating switch is to provide isolation between maintenance equipment and energized equipment. Due to the absence of a dedicated arc extinguishing device, an isolating switch cannot be used to connect load currents (although it can handle small load currents) or interrupt short-circuit currents.

An isolating switch is primarily composed of the following parts:

  1. Support base: It connects and fixes the conductive parts, insulators, transmission mechanisms, and operating mechanisms as a unified whole, providing support and fixation.
  2. Conductive parts: These include contacts, blades, and terminals, and their role is to conduct electric current.
  3. Insulators: These include support insulators and operating insulators, providing insulation between the conductive parts and the ground.
  4. Transmission mechanism: Its function is to receive the torque from the operating mechanism and transmit the motion to the contacts through linkages, gears, or operating insulators, enabling the opening and closing operations.
  5. Operating mechanism: It provides the energy required for the manual, electrical, pneumatic, or hydraulic actuation of the isolating switch.


PV Firefighter Safety Switch

Firefighter Safety Switch


Causes of overheating in isolating switch contacts:

  1. Overloading of the isolating switch: Adjusting the load or replacing the isolating switch with a higher capacity should be considered.
  2. Oxidation of the contact surfaces, leading to increased contact resistance: Remove the oxidation layer using fine sandpaper (grade 0), and apply a neutral grease or conductive paste.
  3. Loose compression springs or loose threads: Check, adjust, or replace the springs as necessary.
  4. Insufficient contact area between the moving and stationary contacts: Proper adjustment should be made.
  5. Improper handling during opening and closing operations, resulting in arcing and burning of the contacts or incorrect contact position: Carefully inspect the contacts during operation.


The test items required before maintenance of an isolating switch are as follows:

  1. Infrared temperature measurement of the isolating switch before power-off, under loaded conditions.
  2. Measurement of the main circuit resistance of the isolating switch.
  3. Electrical operation and manual operation of the isolating switch.

DC Load Switch-Disconnectors

DC Load Switch-Disconnectors


Common faults and abnormalities in isolating switches include:

  1. Loose tightening components or improper contact alignment, resulting in overheating or welding of contact parts (such as connectors or contacts).
  2. External damage or cracks in ceramic insulators, base fractures, and detachment of pin-type ceramic insulators due to poor quality or natural aging of adhesive joints.
  3. Sticking or malfunctioning operation, incomplete closing or opening, or the isolating switch stopping in an intermediate position during operation.
  4. Failure of the transmission mechanism or electric operation, resulting in out-of-phase closing or self-tripping of the isolating switch.
  5. Burnout of the motor, failure of the contactor, or inability to operate remotely.
  6. Improper positioning of auxiliary contact conversion.
  7. The occurrence of flashovers, discharges, ground faults, resulting in burn marks, and in severe cases, short circuits, explosion of ceramic insulators, and tripping of circuit breakers, especially under severe pollution conditions. Among these, the most common faults are insulator fractures, overheating of conductive circuits such as contacts and terminals, failure of electric operation, out-of-phase closing, and incomplete closing. Heating of conductive circuits, operational obstacles, and insulator failures are the main faults encountered during the operation of isolating switches.