CCR Main Contactor

A CCR Main Contactor is an electrically operated switching device that connects the Constant Current Regulator (CCR) to the AC mains supply. It is the single largest power-switching component in the CCR's input compartment, and is the component referred to as the "Main Contactor" in manufacturer documentation for units such as the ATG Micro 100+/200 and Siemens/ADB L-828 series regulators.

The contactor is typically controlled by the ALCMS, a PLC, or a local control panel, enabling remote start/stop of the CCR and automatic isolation during fault conditions. It provides overcurrent and short‑circuit protection coordination together with an upstream circuit breaker. Because the CCR feeds the series lighting circuit through an internal isolation transformer, opening the Main Contactor removes excitation from that transformer and de‑energises the output — a separate contactor switching the high‑voltage series circuit itself is not standard practice, since interrupting a live constant‑current loop under load can generate dangerous transient voltages. CCRs instead ramp output current down to zero before the Main Contactor opens in a normal shutdown. The contactor is designed for frequent operation and must withstand the high inrush currents and transient voltages characteristic of AGL power systems.

The Main Contactor exists to let a CCR be started, stopped, and isolated remotely and automatically, rather than requiring a technician to physically operate a switch at the equipment shelter every time the regulator needs to be energised or taken offline. It sits between the mains supply and the CCR's input terminals, coordinating with the upstream circuit breaker for overcurrent protection while giving the ALCMS a single, reliable point of remote control over the whole regulator. Because ALCMS-driven remote control means this contactor may cycle far more often than a manually operated switch would, its rating for frequent operation and high inrush tolerance is central to the component's purpose, not incidental to it.

Switching or isolating an energised series lighting circuit is a separate function from anything the Main Contactor does, and is handled by purpose-built circuit selector switchgear that only operates once the CCR's output has already been ramped to zero — never by a general-purpose load-breaking contactor. See the related Circuit Selector Cabinet component for that function.

CCR Main Contactors are installed in airfield electrical rooms, equipment shelters, and AGL power centres. They are used in every AGL installation that requires remote or automated control of CCRs, including:

• Runway Lighting Systems: Controlling CCRs that power runway edge, centreline, threshold, and touchdown zone lighting circuits.
• Taxiway Lighting Systems: Managing CCRs for taxiway edge, centreline, and stop bar circuits.
• Approach Lighting Systems: Controlling CCRs for approach lighting configurations (ALSF-1, ALSF-2, MALSR, etc.).
• Integration with ALCMS: Allowing remote start/stop and automatic fault isolation from the central control system.
• Redundant CCR Schemes: Allowing the ALCMS to start the standby CCR's Main Contactor and bring it to full ramp before the primary CCR is ramped down and its own Main Contactor opened, supporting a controlled changeover rather than a live circuit break.
• Maintenance Isolation: Providing a visible break and a safe means of de-energising the CCR for servicing, without interrupting the entire lighting system.

The Main Contactor is installed within the CCR's input compartment or immediately adjacent to the CCR cabinet in the equipment shelter, wired between the mains supply (and its upstream circuit breaker) and the CCR's input terminals. Mounting within the same enclosure as the CCR keeps the high-current wiring run short, reducing both voltage drop and the length of exposed conductor carrying the CCR's input current. Control wiring from the ALCMS, PLC, or local control panel is run to the contactor coil separately from the power wiring, kept clearly labelled given that a CCR bank in a larger equipment room may have several Main Contactors operating independently. Because this contactor is expected to cycle far more frequently under remote control than a manually switched device would, its mounting position allows the clearance and ventilation the manufacturer specifies for contactors rated for frequent operation, rather than the tighter spacing that might suit an infrequently switched device.

The CCR Main Contactor is a single electromagnetic contactor with a coil that, when energised, closes the main contacts to connect the CCR to the mains supply. De‑energising the coil opens the contacts, fully isolating the CCR.

Key functional aspects include:

• Closing: Connected between the mains supply (typically 400V AC, 3‑phase) and the CCR's input terminals, and commanded by the ALCMS, a PLC, or a local start/stop signal. When closed, mains power reaches the CCR, which then runs its own soft-start sequence to bring the series circuit up to the commanded brightness step.
• Normal opening: Before the contactor is commanded open in a routine shutdown, the CCR ramps its output current down to zero. Once at zero, opening the Main Contactor removes mains power with no arc or transient on the high-voltage side, since the isolation transformer's secondary is already unexcited.
• Fault opening: On detection of an internal fault (overcurrent, earth fault), the CCR's protection circuitry can command the contactor open immediately, independent of the ramp sequence — this is the one situation where the contactor may interrupt real current, and it is coordinated with the upstream breaker's trip characteristics.
• Auxiliary Contacts: The contactor provides auxiliary contacts (normally open and normally closed) for status feedback to the ALCMS or control system, indicating whether it is closed or open.
• Arc Suppression: The contactor is fitted with arc chutes to safely quench the arc that can form when interrupting mains current during a fault trip.

The Main Contactor is the physical enable point beneath every layer of control logic described elsewhere in the AGL system — nothing the ALCMS or the CCR's own regulation can do matters if this contactor isn't closed. Command authority for closing and routine opening sits with the ALCMS (or a local start/stop station), coordinated with the CCR's soft-start and ramp-down sequencing so the contactor is never asked to make or break current under load in normal operation. Opening on fault, however, is not purely a command response: it is driven directly by the CCR's own protection circuitry, so an overcurrent or earth fault trips the contactor immediately regardless of what the ALCMS has commanded, faster than a control-room decision loop could react. This is a deliberate division of authority — the ALCMS decides when the circuit should normally be live, while the CCR's own protection decides, independent of any external command, when it must not be. Auxiliary contact feedback closes the loop by reporting actual contactor position back to the ALCMS, so the control system's picture of "circuit energised" is always confirmed by hardware state rather than assumed from the last command sent.

The contactor is built with silver-alloy or silver-tungsten main contacts sized for the three-phase mains current feeding the CCR, and is engineered for the mechanical and electrical life needed to withstand frequent remote-controlled cycling rather than the occasional manual switching a simpler installation might see. It is typically mounted within the CCR's own input compartment on a DIN rail or subpanel, positioned to keep the conductors between contactor and CCR as short as practical, and spaced according to the manufacturer's clearance and ventilation requirements so heat from frequent switching doesn't shorten contact life. Indoor cabinet installations use an IP20 enclosure relying on the CCR shelter's environmental control, while contactors in unconditioned or outdoor enclosures step up to an IP54-rated weatherproof housing. Control coil wiring is terminated separately from the power connections at a dedicated low-voltage terminal block, and auxiliary contacts used for remote status feedback are wired through their own cable entry to keep control signals isolated from the switched power conductors.