How are connectors tested at commissioning?
Connectors are made on site and are the usual weak point of a circuit. Each one is checked for fit and seal, for low contact resistance and for sound insulation, and its result is recorded by ID.
Cable is made in a factory; connectors are made on site, in pits and trenches, by hand. That makes them the most common weak point on an airfield circuit. A poor contact gives a high-resistance joint that heats up or opens, and a damaged seal lets in moisture and leads to an earth fault. Connector testing finds those faults before the circuit is energised.
Each connector is first inspected: the right type for the cable and transformer lead, clean and undamaged, fully mated, with its seal fitted and the cable free of strain. A low-resistance ohmmeter then measures the contact resistance across the connection, and the insulation resistance from conductor to earth proves the sealed assembly is dry. All of this is de-energised, with the circuit isolated and proved dead, and is done before the pit is closed. Never pull apart or work on a connector on a live loop.
- Inspect. Check the connector type against the design, look for damage or dirt, and confirm it is fully mated, with the seal in place and no strain on the cable.
- Make and seal. Assemble and seal the connector to the manufacturer’s procedure. Keep the surfaces clean and dry while it is made.
- Check contact. With the circuit isolated, measure continuity across the connection with a low-resistance ohmmeter and compare it with similar connectors.
- Check insulation. Measure insulation resistance from conductor to earth. The value should be high and steady, as part of the cable and run tests. Discharge the conductor after the test before it is touched.
- Remake if poor. If a reading is out of line, remake the connector with a new seal rather than just re-tightening it, and test it again.
- Record. Log each connector by ID and location with the readings, date and instrument. This is the baseline for later tests.
What the readings suggest
Low and consistent
Contact resistance is low and in line with similar connectors, and insulation resistance is high and steady. Record it and carry on.
High or unsteady contact resistance
Suspect a poor crimp or contact, dirt, or damaged pins. A connector like this can heat up or open later, so remake it.
Open circuit
The connector is not fully mated, or a conductor has pulled out or broken. Re-mate or remake it, then test again.
Low insulation resistance
Moisture has probably got in, through a damaged seal, a cut jacket or a wet assembly. Dry it out or remake it with a new seal.
One differs from the rest
Compare similar connectors. One that stands out may be faulty even if it is within limits.
Always record
Log each connector by ID and location, with the readings and date, so later tests have a baseline.
Frequently Asked Questions
Q1What is connector testing in AGL commissioning?
It is a set of de-energised checks on each connector of a new circuit: inspection for type, mating and seal, a contact-resistance measurement across the connection, and an insulation-resistance test to earth. Each result is recorded by connector ID.
Q2Why are connectors the weak point of a circuit?
Unlike factory-made cable, connectors are assembled on site, often in a wet pit or trench. A poor crimp, a speck of dirt or a damaged seal is easy to introduce, and the result is a high-resistance contact or moisture ingress that later causes an open circuit or an earth fault.
Q3What does contact resistance tell you?
A low-resistance ohmmeter measures the resistance across the connection. It should be low and close to the readings for similar connectors. A high or unsteady reading shows a poor contact, which can overheat or open in service.
Q4Why test before the pit is closed?
A faulty connector is quick to remake while the pit is open and the cable is accessible. Once the pit is backfilled and the circuit is energised, finding and fixing the same fault takes much longer.
Q5Should a poor connector just be tightened?
No. Re-tightening hides the cause. The connector is remade to the manufacturer's procedure with a new seal, then tested again, because a damaged contact or a compromised seal will not be cured by tightening.
Q6What contact resistance and insulation values are acceptable?
They depend on the connector type, the cable, the manufacturer's data and the project specification, so this page gives no fixed figures. Use the values in the specification, and compare with similar connectors.
Q7How does this differ from connector inspection and cable testing?
Connector inspection is a routine visual check in maintenance. Cable testing covers the cable lengths and jointed runs. Connector testing measures each connection itself, at commissioning, to prove it is mated, sealed and sound and to set its baseline.
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