CCR Bypass/Isolation Contactor

A CCR Bypass/Isolation Contactor is a dual‑purpose switching device used in AGL power distribution systems to provide both a bypass path around a CCR and a visible isolation point for maintenance. It typically comprises a set of mechanically and electrically interlocked contactors that can connect the series circuit directly to an alternate power source (such as a second CCR or a spare regulator) or completely isolate the CCR from the circuit, allowing safe servicing.

The bypass function is critical for maintaining airfield lighting continuity during CCR maintenance or failure. When a CCR needs to be taken out of service, the bypass contactor closes, routing the series circuit to the standby or backup CCR, while the isolation contactor opens to disconnect the faulty CCR. The isolation contactor also provides a visible break (when open) to ensure the circuit is de‑energised for safe maintenance work. This assembly is often integrated into the CCR cabinet or installed as a separate panel adjacent to the CCR bank.

This assembly exists to solve a conflict that would otherwise be unavoidable: a CCR that needs maintenance must be safely de-energised for the technician's protection, but the series circuit it feeds may need to stay lit for continued airfield operations. By pairing a bypass path to a standby regulator with a true isolating break on the faulty unit, the device lets both needs be met at once — the circuit keeps running on the alternate CCR while the original is genuinely disconnected, not just switched off at the control level. The isolation contactor's visible break specifically exists for technician safety, giving unambiguous physical confirmation that the CCR is de-energised, since a technician working on a device believed to be off but still electrically connected faces a serious risk that a control-level shutoff alone cannot fully rule out.

CCR Bypass/Isolation Contactors are installed in airfield electrical rooms, equipment shelters, and AGL power centres where redundancy and maintenance flexibility are required. They are used in:

• Redundant CCR Configurations: Where a standby CCR is available to take over the load if the primary CCR fails or requires maintenance.
• Hot‑Swap Maintenance: Allowing a CCR to be replaced or serviced without interrupting the lighting circuit (provided a standby CCR is available).
• Precision Approach Runways (CAT I, II, III): Where high availability is mandated, and bypass capability is essential to minimise downtime.
• Critical Lighting Circuits: Runway edge, centreline, threshold, and approach lighting systems that must remain operational at all times.
• Integration with ALCMS: Enabling remote bypass and isolation control, with status feedback to the central control system.
• Testing and Commissioning: Allowing new CCRs to be tested while the existing regulator remains in service, using the bypass to switch between them.

The assembly is installed in the equipment shelter as part of the CCR bank, either integrated into the CCR's own cabinet or mounted as a separate panel immediately adjacent to it, with the bypass and isolation contactors wired between the primary CCR, the standby CCR, and the outgoing series circuit. Positioning keeps the visible isolation break within clear sight of anyone working on the de-energised CCR, since the whole purpose of that break is to give unambiguous physical confirmation that the unit is disconnected before maintenance begins. Control wiring to the ALCMS or a local control panel is run alongside other CCR control cabling, allowing remote bypass switching, with the contactor's status feedback clearly labelled to the specific CCR pairing it manages in an equipment room that may house several redundant regulator sets. Because switching a fault onto a standby CCR needs to happen quickly and correctly, the interlocking between bypass and isolation contactors is verified during commissioning by testing an actual changeover, rather than assumed correct from the wiring diagram alone.

The bypass/isolation contactor assembly consists of three main contactor groups:

• Isolation Contactor (Normal Path): Connects the CCR's output to the series circuit. When closed, the CCR feeds the circuit. When open, the CCR is isolated from the circuit.
• Bypass Contactor: Connects an alternate power source (e.g., a standby CCR or a direct mains feed, though the latter is rare in AGL) to the same series circuit. When closed, the circuit is powered by the alternate source.
• Interlocking: Mechanical and electrical interlocks ensure that the isolation and bypass contactors are never closed simultaneously, preventing two CCRs from being paralleled (which would cause circulating currents and overloads).

The normal operating state has the isolation contactor closed and the bypass contactor open. When a transfer is required (e.g., for maintenance), the control system (or manual operator) first closes the bypass contactor to connect the standby CCR, then opens the isolation contactor to disconnect the primary CCR. This "make‑before‑break" sequence ensures no interruption to the lighting circuit. Conversely, when returning to normal operation, the isolation contactor is closed first, then the bypass contactor is opened. The assembly also includes auxiliary contacts for status indication (position feedback) to the ALCMS.

This assembly sits above the loop-level control described for individual fixtures — it decides which CCR feeds the circuit, not what current the circuit runs at. A transfer can originate two ways: a technician initiating a manual changeover for maintenance, or an automatic transfer triggered when the CCR regulator monitor (L-827) reports a regulator failure that the ALCMS has been configured to act on without waiting for manual intervention. Either way, the make-before-break sequencing and mechanical interlocking are what make the swap safe to leave to automation — the ALCMS never has to time the transfer itself, only issue the "transfer to standby" command and read back the resulting contactor positions from the auxiliary contacts. Because the standby CCR is a physically separate regulator, this level of redundancy protects against a CCR failure that would otherwise take the entire circuit dark, which is a different failure class from the individual fixture or transformer faults that ordinary loop-voltage monitoring is designed to catch.

The bypass and isolation contactors are built as a matched pair, each with silver-alloy or silver-tungsten contacts sized to interrupt the CCR's rated series-circuit current and withstand the open-circuit voltage without excessive arcing, mounted on a common frame or DIN rail within a shared enclosure so their mechanical interlock can be built directly into the frame geometry. The mechanical interlock is a rigid linkage or interposed lever between the two contactor bodies that makes it physically impossible for both to be closed at once, backed by an electrical interlock using each contactor's auxiliary contacts wired into the other's coil circuit as a second, independent line of defence. Indoor installations use an IP20 open-frame or ventilated panel enclosure sized for the airflow the contactors need under frequent switching, while outdoor or unconditioned equipment shelters use a weatherproof IP54 enclosure with a viewing window so the visible isolation gap can be confirmed without opening the cabinet. Control wiring terminates at a separate, clearly labelled terminal block from the high-current power connections, and auxiliary contact wiring for remote status feedback is routed through its own gland or conduit entry to keep low-voltage control signals segregated from the switched series-circuit conductors.