How is a new cable tested at commissioning?
A staged set of tests that proves a new primary cable survived laying and jointing: each length is checked before it is joined, the whole run is checked after, and every result is recorded against the cable ID.
A primary cable can be perfect on the drum and damaged by the time it is in the ground. Pulling, bending, trench backfill and jointing can all harm it. Cable testing at commissioning is therefore done in stages, so that a fault is found while it is still easy to reach and cheap to fix.
First the drum and cable ends are inspected. Then each length is tested for continuity and insulation resistance before it is jointed, and the result is compared with the manufacturer’s drum record. After the joints and terminations are made, the whole run is tested again. A withstand (proof) test is added only if the specification calls for it, at the voltage and time it states. All testing is de-energised, with the cable isolated and proved dead. Discharge the cable after any DC test before touching it, and record every result against the cable ID.
- Inspect. Check the cable type and rating against the design, look for damage, and confirm the cable ends are sealed against moisture. Keep the manufacturer’s test record.
- Test each length. With the cable isolated, measure continuity and insulation resistance on each length before it is jointed, and compare with the drum record.
- Joint and terminate. Make each joint and termination to the approved procedure, then keep the open ends sealed until the tests are done.
- Test the jointed run. Measure continuity and insulation resistance across the whole run to prove the joints and terminations.
- Withstand test, if specified. Apply the specified voltage for the specified time, with the area barriered, then discharge the cable.
- Record. Log each length and the whole run by cable ID, with the value, date, instrument and joint references, and update the as-built records.
What the readings suggest
Matches the drum record
Continuity is complete and insulation resistance is high and steady, in line with the drum record and the specification. Record it and carry on.
Low before jointing
Suspect damage in laying or moisture at an unsealed end. Do not joint it. Trace the fault, then repair or replace the length.
Low or open after jointing
The cable passed alone, so suspect a joint or termination. Test each half of the run to narrow it down, then remake it.
Fails the withstand test
The insulation has a defect. Find it, repair it, and repeat all the tests, not just the withstand test.
One length differs from the others
Compare lengths of similar size. A length that stands out may be damaged or wet, even if it is within limits.
Always record
Log each length and the whole run by cable ID, with joint references. This is the baseline for later tests.
Frequently Asked Questions
Q1What is cable testing in AGL commissioning?
It is a set of de-energised tests on a new primary cable, carried out in stages, to show that the cable survived laying and jointing and is safe to energise. The tests are continuity, insulation resistance and, if the specification requires it, a withstand test.
Q2Why is the cable tested in stages?
A fault is far easier and cheaper to fix before a length is jointed and buried. Testing each length first shows whether the cable is sound, and testing the whole run afterwards shows whether the joints and terminations are sound.
Q3Why test each length before jointing?
Once lengths are jointed, a fault could be in any length or any joint, so tracing it takes longer. A length that fails on its own is replaced or repaired before it is joined, and the drum record gives a reference to compare it with.
Q4Is a withstand test always required?
No. It is carried out only if the project specification calls for it. The voltage, the time and the pass criteria all come from the specification and the cable rating. It is done by a competent person with the area barriered, and the cable is discharged afterwards.
Q5What test voltages and limits apply?
They depend on the cable rating, the manufacturer's data, the applicable standard and the project specification, so this page gives no fixed figures. Use the values stated in the specification for the job.
Q6How does this differ from the continuity and insulation-resistance entries?
Those entries describe the tests themselves on a loop. Cable testing is the staged programme that applies them to the cable, length by length and again after jointing, and adds the withstand test when specified.
Q7How does this differ from cable testing in maintenance?
At commissioning the tests prove a new cable and record its baseline, and faults are cheap to fix because the trench is open. In maintenance the cable is already in service, and the same tests are compared with that baseline to spot ageing or damage.
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