Secondary Connector
The receptacle (female) half of the two‑pole L‑823 connector system, terminating the secondary (low‑voltage) lead of an isolating transformer or a fixture's lead wire. It provides a secure, waterproof interface for the mating plug, ensuring reliable, low‑resistance connections between the transformer and the fixture in the harsh airfield environment.
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What Is It?
The Secondary Connector (also known as the L‑823 two‑pole receptacle or female connector) is the two‑pole half of the waterproof connector system used for secondary circuit connections in airfield ground lighting (AGL) systems — that is, the low‑voltage circuit downstream of an isolating transformer. It is factory‑ or field‑molded onto an isolating transformer's secondary lead or a fixture's lead wire, providing a receptacle that accepts the mating secondary plug.
The connector features a threaded outer shell that mates with the plug's coupling ring, compressing internal O‑rings to achieve an IP68 submersible seal. The two contacts—typically gold‑ or tin‑plated brass sockets—receive the plug's pins, carrying the secondary current with minimal resistance. The secondary connector is designed for repeated mating cycles and provides a robust, corrosion‑resistant interface for isolating‑transformer‑to‑fixture connections.
Purpose & Function
The secondary connector's role is to give an isolating transformer's secondary lead, or a fixture's lead wire, a stationary, repeatedly matable socket for the secondary circuit, so that connecting or disconnecting a fixture during maintenance never requires disturbing the transformer's own termination. Because this half of the connector stays in place for the life of the equipment while the mating plug is what gets handled during servicing, its contacts and seals are engineered specifically for durability across many mating cycles rather than for a single, permanent joint. This division of roles between a fixed receptacle and a removable plug is what allows AGL fixtures to be serviced or swapped without re-terminating the transformer's secondary lead each time.
Where Is It Used?
The secondary connector is used throughout the airfield wherever an isolating transformer's secondary lead needs to connect to a fixture's lead wire, including:
- Isolating Transformer Secondary Leads: Every series isolation transformer has one secondary lead, terminated in a secondary connector, that mates with the fixture's lead-in plug.
- Fixture Lead Wires: Runway, taxiway, and approach light fixtures terminate their lead wire in the mating plug that connects to the transformer's secondary receptacle.
- Elevated and Inset Light Connections: Elevated edge lights, inset centerline and touchdown zone lights, and similar fixtures all connect to their isolating transformer through this same secondary interface.
- Sign and Wind Cone Circuits: Illuminated signs and obstruction/wind cone lighting fed from a series circuit isolating transformer use the same secondary connector arrangement.
- Secondary Extensions and Splices: Where a fixture lead needs lengthening or a serviceable in-field splice is required in the secondary circuit, secondary connector kits are used to join two secondary leads.
- Retrofit and Upgrades: Replacing a degraded or incompatible secondary connector when a fixture is upgraded or an isolating transformer is replaced.
The connector is available in factory-molded (cable‑mount) and field‑installable kit forms, with termination options for soldering, crimping, or the connector kit's own molding process. It is rated for continuous operation at 6.6A or 20A on the secondary (low‑voltage) side of the isolating transformer.
Installation & Location
The connector (receptacle) terminates the isolating transformer's secondary lead or the fixture's own lead wire, using the same cable‑mount (pigtail) or, where the design calls for it, panel‑ or flange‑mount configuration as the corresponding plug assembly, and positioned so the mating face remains accessible once the transformer and fixture are installed in their pit or base can. Wiring from the connector's socket contacts back to the transformer winding or fixture lamp holder is completed and sealed during factory molding or field kit assembly, with the connector's own O-ring seals compressed to maintain the assembly's IP68 rating. Because this half of the connector stays fixed to its lead while the plug is what gets handled during fixture servicing, its mounting location is chosen with enough clearance around it for a technician to thread and unthread the mating plug without obstruction from nearby cabling or equipment. Periodic disconnection for testing or fixture replacement is anticipated in the layout, keeping the connector clear of standing water where the pit or base can allows.
How Does It Work?
The secondary connector provides a secure, low‑resistance electrical interface while maintaining a waterproof seal. Its design incorporates several key functional elements:
- Two‑Socket Contact System: Two machined brass sockets (female) with gold or tin plating provide low‑contact‑resistance mating with the plug's pin contacts. The sockets are designed for gas‑tight connections that resist corrosion and maintain consistent contact force.
- Threaded Outer Shell: The connector body features external threads that accept the plug's coupling ring. When tightened, the ring compresses the internal seals, locking the connection against vibration and accidental disconnection.
- Elastomeric Seals: Multiple O‑rings (typically silicone or EPDM) provide IP68 sealing when the connector is fully mated and torqued. The seals are compressed by the coupling ring to form a watertight barrier.
- Mounting Options: The connector is available with various mounting configurations: panel‑mount (with a flange and gasket for bulkhead installation), flange‑mount (with screw holes), or cable‑mount (with a pigtail and gland).
- Durable Housing: The connector shell is typically made of corrosion‑resistant materials such as brass, bronze, or high‑grade polyamide with UV stabilizers, ensuring longevity in outdoor environments.
When properly installed with the recommended torque (3.5–5.5 N·m), the secondary connector provides a connection that can remain submerged in water for extended periods without degradation. Its low contact resistance ensures minimal voltage drop and heating, critical for maintaining the performance of the constant‑current series circuit.
System Architecture & Control Logic
The secondary connector has no control logic of its own — it is a purely passive electrical interface that sits in series within the CCR-regulated secondary circuit, between the isolating transformer and the fixture. Because it carries the loop's current downstream of the transformer, its condition is never monitored directly: the CCR only sees the aggregate voltage across the entire primary loop, so a degraded contact — corrosion on the sockets, an under-torqued coupling ring, or a failed O-ring letting in moisture — shows up only as a small rise in loop voltage at constant current, indistinguishable at the CCR from any other high-resistance connection on the circuit until a technician isolates it with local testing. Whichever mounting configuration is used (covered below), the connector's role in the control chain is identical: a fixed, non-switching link that either passes the secondary current cleanly or, if it degrades, adds resistance the CCR compensates for by holding voltage up, until the fault is traced to that specific connector in the field.
The connector is invisible to the control loop — until it fails
Mounting Configuration Options
Panel-Mount
Flange + gasket for bulkhead installation on equipment panels
Flange-Mount
Screw-hole flange for direct enclosure or transformer housing mounting
Cable-Mount (Pigtail)
Short factory pigtail with compression gland for inline splicing
Result: Whichever way it's fixed to the equipment, the same two-socket contact system and O-ring seal accept the mating plug — a stationary, field-repairable interface rated for ≥ 500 mating cycles at 6.6A or 20A.
Physical Construction
The secondary connector's threaded outer shell and two gold‑ or tin‑plated brass socket contacts are moulded or machined as a single fixed unit, installed onto the transformer, junction box, or panel it serves either during factory manufacture or as a field‑fitted receptacle. Internal O‑rings sit at the point where the plug's coupling ring threads onto the shell, compressing to form the seal once the two halves are mated, and a separate gasket or seal is used where the shell itself passes through the equipment wall to keep moisture from tracking in behind it. Because the socket contacts are recessed inside the threaded shell rather than exposed, they are protected from accidental contact and corrosion whenever the connector is unmated, and the shell's threading is sized for the same coupling ring pitch as the mating plug so the pair can be repeatedly mated and separated without galling or cross‑threading.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Rated Current (Continuous) | 6.6A or 20A (depending on variant) |
| Rated Voltage (AC) | Up to 600V (secondary/low-voltage side, per FAA L‑823 two-pole spec) |
| Contact Material | Machined brass with gold or tin plating |
| Contact Resistance (initial) | ≤ 0.5 mΩ per contact pair |
| Shell Material | Brass, bronze, or UV‑stabilized polyamide |
| Sealing Material | Silicone or EPDM O‑rings |
| Protection Class (mated) | IP68 (submersible, continuous) |
| Operating Temperature | -40°C to +85°C |
| Mounting Options | Panel‑mount (flange), cable‑mount (pigtail), bulkhead |
| Mating Cycles | ≥ 500 cycles (gold‑plated contacts) |
| Torque (coupling ring) | 3.5 – 5.5 N·m (recommended) |
| Standards | FAA AC 150/5345-26 (L‑823), IEC 63067, SAE AS81714 |
Electrical Requirements
| Requirement | Typical Value |
|---|---|
| Circuit Type | In-line connector on the secondary (low-voltage) side of an isolating transformer or on control/data cabling — not itself a powered device |
| Rated Current | 6.6A or 20A (variant dependent), continuous |
| Rated Voltage | Up to 600V (secondary/low-voltage side, per FAA L‑823 two-pole spec) |
| Contact Resistance | ≤ 0.5 mΩ per contact pair (initial) |
| Sealing / IP Rating | IP68 when mated (submersible, continuous) |
| Earthing/Grounding | Metal shell variants bonded to the connected cable's earth/shield where fitted |
| Fault Protection | None internal — protection is provided at the source (CCR/transformer/panel), not by the connector |
| Standards | FAA AC 150/5345-26 (L-823), IEC 63067, SAE AS81714 |
Applicable Standards
FAA AC 150/5345-26 (L-823)
Specification for plug and receptacle cable connectors; this component is the two-pole secondary (transformer-to-fixture) variant
IEC 63067
General requirements and tests for plugs and receptacles used in aeronautical ground lighting
SAE AS81714
Terminal junction system for aerospace applications
ICAO Annex 14
General requirements for AGL circuit components
Installation Requirements
Panel/Flange Mounting
MechanicalMount the connector on the equipment it serves using the same panel-mount, flange-mount, or pigtail configuration as the mating plug, positioned so the mating face stays accessible once installed.
Internal Wiring Termination
ElectricalWire the connector's socket contacts back to the equipment's internal terminals and seal before the enclosure is closed.
O-Ring Seal Compression
MechanicalConfirm the connector's O-ring seals compress evenly against the enclosure wall or cable entry before final fixing, to maintain the waterproof rating.
Secondary Voltage Rating Match
ElectricalConfirm the connector's voltage and current rating match the isolating transformer or circuit it will carry before connection.
Mating & Locking Engagement Check
MechanicalConfirm the mating plug locks and seats fully home before the connection is considered complete.
Pre-Energisation Sign-off
DocumentationRecord mounting location, wiring terminations, and seal condition as-built before the enclosure is closed.
Testing & Commissioning
Insulation Resistance Test
Pre-EnergisationMegger-test through the mated secondary connector pair before backfill, confirming insulation resistance clears the acceptable minimum.
Continuity & Contact Resistance Test
Pre-EnergisationVerify continuity through the mated connector and measure contact resistance, ruling out a poorly seated pin or corroded contact.
Mating & Locking Engagement Check
Pre-EnergisationConfirm the plug and receptacle are fully mated and any locking feature is engaged, preventing vibration-induced disconnection.
Waterproof Seal Verification
Pre-EnergisationInspect the O-ring or gasket seal at the mating face for correct seating before the connector is buried or placed in a fixture base.
Secondary Voltage Verification
EnergisationWith the isolating transformer energised, confirm secondary voltage is present at the connector and matches the transformer's rated ratio.
Documentation & As-Built Sign-off
Final AcceptanceRecord insulation, continuity, and voltage readings alongside the connector's as-built location in the commissioning dossier for handover.
Inspection & Maintenance
Contact Resistance Test
AnnualMeasure resistance across mated contact pairs against the ≤0.5mΩ specification, flagging corrosion or spring-tension loss before it causes overheating.
O-Ring Inspection
AnnualCheck silicone or EPDM O-rings for hardening, cracking, or compression set from UV and temperature cycling, and replace with fresh silicone grease applied.
Contact Cleaning
Semi-annualClean socket contacts with approved contact cleaner and re-apply dielectric grease, particularly on connectors exposed to saltwater or chemically aggressive environments.
Coupling Ring Torque Check
AnnualVerify the coupling ring is torqued within the 3.5–5.5 N·m range and inspect threads for cross-threading damage that could prevent a proper mate.
Spring Tension Check
AnnualAssess contact spring retention force on connectors approaching or exceeding their rated mating cycles, replacing any unit with reduced contact force.
Mounting Gasket Inspection
AnnualFor panel-mount units, check the flange gasket condition and mounting screw torque to prevent moisture ingress at the mounting interface.
Thread Protection Check
Semi-annualConfirm protective caps are fitted to unmated connectors in storage or spare stock to prevent thread damage and contamination ingress.
IP Rating Verification
AnnualConfirm the mated connector maintains its IP68 submersible rating by checking for water ingress signs at the interface after wet-season exposure.
Common Field Issues
Corrosion of Socket Contacts
Despite plating, sockets can corrode in saltwater or chemically aggressive environments, increasing contact resistance. Regular inspection and cleaning with contact cleaner, along with application of dielectric grease, are recommended.
O‑Ring Hardening and Cracking
O‑rings can degrade due to UV exposure, temperature cycles, or chemical attack. Replace O‑rings periodically and use silicone grease to prolong their life.
Loss of Contact Spring Tension
Over time and with repeated mating cycles, the socket contacts can lose spring tension, reducing contact force and increasing resistance. This can cause overheating and intermittent connections. Replace connectors showing reduced contact retention.
Cross‑Threading of External Threads
Cross‑threading of the connector's external threads can make mating with the plug coupling ring difficult or impossible. Protect threads with caps when not in use and inspect before mating.
Moisture Ingress via Mounting Interface
For panel‑mount connectors, the sealing gasket between the connector flange and the equipment housing can degrade. Ensure the gasket is in good condition and the mounting screws are properly torqued.
Damaged or Bent Socket Contacts
Improper insertion of the plug can bend or damage the socket contacts. Use alignment guides and insert the plug straight to avoid damage. Replace connectors with damaged contacts.
Troubleshooting Guide
Intermittent Connection or Overheating at the Connector
Connector Will Not Mate or Seat Fully
Water Ingress at the Connector
Fixture Dark Due to Damaged Socket Contacts
Moisture Ingress via a Panel-Mount Interface
Failure Modes & Root Causes
Contact Corrosion or Lost Spring Tension
Cross-Threaded Coupling
O-Ring Seal Degradation
Bent or Damaged Socket Contacts
Panel-Mount Gasket Degradation
Safety & Operational Notes
Series Circuit Isolation
Electrical SafetyAGL series circuits can carry several kV. De-energise and lock out the CCR, then verify zero energy before mating, unmating, or servicing a secondary connector.
PPE & Insulated Tools
Personnel SafetyUse insulated tools and appropriate PPE when handling connector contacts on a series circuit, particularly when the connector is on equipment that has recently been in service.
Avoid Cross-Threading on Mating
OperationalAlign the plug and receptacle carefully and thread the coupling ring by hand before tightening, to avoid cross-threading that can damage the seal and compromise the IP68 rating.
Inspect O-Rings and Seals Before Reassembly
OperationalCheck O-rings and gaskets for damage, dirt, or degradation before mating a connector, and replace them rather than reusing a compromised seal.
Insulation Test Before Re-Energisation
Electrical SafetyMegger test the affected loop after any connector work before restoring power, since a residual fault at re-energisation can trip the CCR or damage healthy equipment on the circuit.
Verify Contact Engagement Before Closing Out
ComplianceConfirm the connector is fully mated and the coupling ring is properly tightened before returning the equipment to service, since a partially mated connector can pass initial testing but fail later under vibration or thermal cycling.
Engineering & Expert Notes
The IP68 Seal Depends on O-Ring Condition, Not Just the Threaded Shell
DurabilityA receptacle's threaded shell can look undamaged and fully engaged while a hardened, nicked, or missing internal O-ring has already compromised the seal; inspect and, where due, replace O-rings on their own service interval rather than judging seal integrity from the outside of a mated connector alone.
Socket Contact Wear Shows Up as Resistance Before It Shows Up as a Failure
TroubleshootingRepeated mating cycles gradually wear the plating on the receptacle's socket contacts, and a worn socket can still make electrical contact while presenting elevated resistance under load; where a loop shows a marginal current or heating issue at a specific connector, don't rule out contact wear just because the connector still measures continuity on a simple ohmmeter check.
Cross-Threading During Mating Damages the Receptacle Permanently
InstallationForcing a plug's coupling ring onto a misaligned receptacle thread can damage the receptacle's shell threads in a way that isn't obvious until the next disconnection attempt; always start the coupling by hand and confirm it threads smoothly before applying any real torque, rather than forcing an initially stiff mating.
Factory-Installed and Field-Installed Receptacles Age Differently
ReliabilityA receptacle installed under controlled factory conditions typically has more consistent seal and contact quality than one terminated in the field; where a specific batch of field-terminated receptacles shows a higher-than-normal fault rate, consider whether the field termination process itself — rather than the connector part — is the root cause.
Fuel and De-Icing Fluid Exposure Degrades Seals Faster Than Weather Alone
DurabilityReceptacles mounted on equipment near taxiway or runway intersections that see heavy de-icing fluid or occasional fuel exposure degrade faster than the general weathering rate would suggest; specify seal materials rated for these specific chemical exposures rather than assuming a standard weatherproof rating covers them.
Track Mate Cycles on High-Turnover Equipment Connections
DocumentationA receptacle on equipment that's frequently disconnected for maintenance — a junction box accessed regularly, for example — accumulates wear on a different timeline than one that's mated once at installation and rarely touched again; keep service records that reflect actual mate-cycle frequency rather than treating all receptacles as aging identically by calendar time alone.
Frequently Asked Questions
Short answers about secondary connectors (L-823 two-pole receptacles): what they do, ratings, torque, standards, maintenance and common faults.
Q1What is a secondary connector?
The secondary connector, also called the L-823 two-pole receptacle or female connector, is the two-pole half of the waterproof connector used for secondary circuit connections downstream of an isolating transformer. It is moulded onto a transformer's secondary lead or a fixture's lead wire and accepts the mating secondary plug.
Q2Why is a repeatedly matable socket needed?
It lets a fixture be connected or disconnected during maintenance without disturbing the transformer's own termination. This half stays in place for the life of the equipment while the plug is what gets handled, so its contact reliability matters.
Q3How does the connector achieve a waterproof seal?
A threaded outer shell accepts the plug's coupling ring, and tightening compresses internal silicone or EPDM O-rings to give an IP68 submersible seal, at −40 °C to +85 °C.
Q4What are the connector's ratings?
Continuous current of 6.6 A or 20 A depending on variant, up to 600 V on the secondary side, initial contact resistance of 0.5 mΩ or less per contact pair and at least 500 mating cycles with gold-plated contacts. Contacts are two gold- or tin-plated brass sockets.
Q5What torque should the coupling ring be tightened to?
3.5–5.5 N·m. Check threads for cross-threading before mating, since damage can prevent a proper mate.
Q6Where are secondary connectors used?
On every series isolating transformer's secondary lead, which mates with the fixture's lead-in plug, and on the fixture lead wires of runway, taxiway and approach lights, including elevated edge lights and inset centreline and touchdown zone lights.
Q7How is the connector mounted?
In cable-mount (pigtail), panel/flange-mount or bulkhead form, positioned so the mating face stays accessible once the transformer and fixture are in their pit or base can.
Q8Which standards apply to secondary connectors?
The main references are FAA AC 150/5345-26 (L-823), IEC 63067 (plugs and receptacles for aeronautical ground lighting), SAE AS81714 and ICAO Annex 14. Always verify the current edition and your approved requirements.
Q9How often should a secondary connector be inspected?
Typical intervals are semi-annual for contact cleaning, and annual for contact resistance, O-ring inspection, coupling ring torque and spring tension checks. Your approved maintenance programme takes precedence.
Q10Why is the connection intermittent or overheating?
Corroded socket contacts, or contacts that have lost spring tension after repeated mating, are increasing resistance. Measure contact resistance, then clean and apply dielectric grease or replace the connector if spring tension is lost.
Q11Why won't the connector mate or seat fully?
Cross-threading has damaged the coupling ring's engagement. Inspect the threads on both halves before another attempt, and replace the half with damaged threads.
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