What is continuity testing?
A de-energised check that a series lighting loop is one unbroken conductive path — proving the circuit is complete before it is switched back on.
Continuity testing proves that a circuit forms an unbroken conductive path. On an airfield series lighting loop, the CCR is switched off, locked out and disconnected, and a low-resistance tester is connected across the two cable ends. Every isolation transformer primary is in that path, so a single break anywhere stops the whole loop reading.
A low, steady reading that matches the commissioning baseline means the loop is continuous. An over-range display (OL) means there is a break, which is found by splitting the loop at pits and connectors and testing each section. Continuity says nothing about insulation, so it is carried out alongside insulation testing.
- Isolate. CCR off, locked out and tagged; confirm the circuit is dead.
- Disconnect. Separate the loop from the CCR and open the cable ends.
- Connect. Attach the tester across the two ends of the loop.
- Read. Compare the value with the commissioning record.
- Locate. If open, split the loop and re-test each section.
- Restore & record. Reconnect, then log the result.
Frequently Asked Questions
Q1What is continuity testing in airfield lighting?
A test that proves a conductor or circuit forms an unbroken electrical path. On a series lighting loop, a low-resistance tester is connected across the cable ends and the loop is read as continuous or open.
Q2Why must the circuit be de-energised first?
Series lighting circuits carry a regulated current at high voltage, and an instrument connected to a live loop is unsafe. The CCR is switched off, locked out and tagged, and the loop is disconnected from it before any test lead is connected. A voltage check on the disconnected loop ends then confirms there is no induced or residual voltage.
Q3What reading shows a good loop?
A low, steady resistance that agrees with the commissioning baseline for that circuit. Total loop resistance depends on cable length and the number of transformers, so the recorded baseline, not a fixed number, is the reference. Resistance also changes with cable temperature, so correct for it before comparing.
Q4What does an open circuit look like on the tester?
An over-range display (often shown as OL) or no reading at all. It means there is a break somewhere in the loop, such as a damaged cable, a failed connector or a failed transformer primary.
Q5How do you locate a break in a series loop?
By splitting the loop at accessible points, such as transformer pits and connectors, and testing each section separately. The section that reads open contains the break, and splitting it again narrows the location.
Q6Does a continuity test find insulation faults?
No. A cable can be perfectly continuous and still have poor insulation. Continuity is one check within cable testing and is normally carried out alongside insulation resistance testing.
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