vacuum contactor

The fundamental difference lies in their mechanical mounting and electrical isolation methods:

• Fixed Type: The contactor is permanently bolted directly onto the switchgear structure or frame. Power connections (busbars or cables) are physically bolted to its terminals.

• Withdrawable Type (Draw-out): The contactor is mounted on a rolling cassette/truck. It connects to the main busbar via automatic self-aligning stab contacts (plug-in contacts) and can be physically racked out without unbolting primary busbars.

ABB vacuum contactors (ConVac7 and ConVac12) are engineered for high-frequency switching and high operational cycles. Common loads include:

• Medium-voltage AC-3 / AC-4 electric motors

• Capacitor banks (single and back-to-back switching)

• Distribution and industrial transformers

• Electric arc furnaces and heavy industrial process switching

The Withdrawable type. A withdrawable unit can be racked out to the "Test/Disconnected" or "Removed" position and swapped with a spare unit in 15–30 minutes. A fixed-type unit requires full power isolation of the section, lock-out/tag-out (LOTO), unbolting primary busbars, and disconnecting hardwired control terminals, which typically takes 2–4 hours. 

Fixed Type: Relies primarily on electrical interlocks and door padlocks to prevent operators from opening panel doors while the contactor is energized.

Withdrawable Type: Uses robust mechanical and electrical safety interlocks. Mechanical interlocks prevent the contactor truck from being racked in or out while the main contacts are closed, and automatically close metallic shutters over live busbar stabs when the unit is withdrawn.

Initial Capital Expenditure (CapEx): Fixed-type contactors are 20%–30% less expensive up front because they lack complex racking mechanics, trucks, and draw-out guide structures.

Operational Expenditure (OpEx): Withdrawable types offer a lower long-term cost of downtime. In continuous process plants (e.g., Oil & Gas, Mining, Power Generation), the cost saved by rapid module replacement during a fault easily outweighs the higher initial investment.