Ranks the likely causes of a series circuit fault from the symptoms and readings, and shows where to look first.
Enter what was seen at the CCR and in the field, plus any loop resistance and insulation readings. The tool checks the readings against the expected values, weighs all the evidence, ranks the likely causes, and suggests what to check next. It also estimates the distance to a short and plans a half-split search of the circuit.
From Calculator #16 or the CCR nameplate. Leave 0 to skip.
Used only when Conductor is set to Custom.
Isolating transformer primaries and joints in the loop, from data sheets. Leave 0 if unknown.
The reading is corrected to the conductor temperature above. Tolerance is your own rule.
Your project specification or maintenance rule. 50 is a placeholder.
The previous reading is optional. The fall threshold is your own rule.
| # | Likely cause | Share of evidence | Where to look |
|---|
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Splits the suspect stretch of the circuit in half at each test, so the faulty section is found in the fewest isolations. Number the fixtures along the loop from the CCR. This planner does not depend on the symptoms or readings.
| Test | Suspect range | Test between fixtures | Left if fault is in first half |
|---|
If the first half tests healthy, the fault is in the second half. Continue with that range.
Each step is shown so the result can be followed and challenged.
The expected loop resistance is the cable resistance at the conductor temperature, plus any other series resistance you enter. The reading is compared with it.
Open circuit means no continuity. Above the tolerance reads as high, below it as low, otherwise normal.
The reading is compared with your minimum. Below the minimum is a fail, up to twice the minimum is a warning, and above that is acceptable. A fall from the previous reading beyond your threshold is flagged as a trend.
Each answer or reading adds weight to the causes it points to, and some answers take weight away. Negative totals are set to zero. A cause's share is its weight divided by the sum of all weights.
Shares show how the evidence divides, not a probability. If the top share is under 30 %, the evidence is mixed and more readings are needed.
For a short between the two conductors of a loop, the resistance seen from the CCR end runs out along one conductor and back along the other.
This assumes both conductors are the same size and ignores transformer primaries between the CCR and the fault, so treat it as a starting point.
Each isolation and test halves the suspect range, so 100 fixtures need at most 7 tests.
| Item | Value |
|---|---|
| #8 AWG, 3,000 m loop, 20 °C | Expected 6.183 Ω |
| CCR trips open, all lamps out | After excavation |
| Loop reading | Open circuit |
| Top cause | Open primary cable |
| Reading of 0.9 Ω instead | Low, short suspected |
| Distance to that short | 218 m |
| Half-split of 100 fixtures | 7 tests |
It does not replace fault-finding procedures, manufacturer guidance or the judgement of a qualified AGL technician. It cannot see faults the inputs do not describe, and it does not model transformer secondaries, reactance or cable capacitance. Weights and thresholds are engineering rules of thumb, and the minimum insulation value and tolerances are yours to set.
Quick answers on how likely series circuit causes are ranked and how the fault is located.
It ranks the likely causes of a series circuit fault from the symptoms you observe and the readings you enter, and shows where to look first. It checks the loop resistance and insulation readings against the expected values, estimates the distance to a short, and plans a half-split search of the circuit. It also produces a PDF report.
A series circuit can carry lethal current even when it looks dead. Isolate, lock out and prove the circuit dead before any resistance or insulation test, and follow your site procedures.
Rexp = ρ20 × [1 + 0.00393 × (T − 20)] × L ÷ 1000 + Rother, where Rother covers isolating transformer primaries and joints in the loop. The reading is compared with it. An open circuit means no continuity, above the tolerance reads as high, below it reads as low, and otherwise it is normal. For example, #8 AWG over a 3,000 m loop at 20 °C gives an expected 6.183 Ω.
The reading is compared with your minimum. Below the minimum is a fail, up to twice the minimum is a warning, and above that is acceptable. A fall from the previous reading beyond your threshold is flagged as a trend. The minimum acceptable value is your own rule, and 50 MΩ is only a placeholder.
Each answer or reading adds weight to the causes it points to, and some answers take weight away, with negative totals set to zero. A cause's share is Share = score ÷ Σ scores × 100. The shares show how the evidence divides, not a probability. If the top share is under 30 %, the evidence is mixed and more readings are needed.
For a short between the two conductors of a loop, the resistance seen from the CCR end runs out along one conductor and back along the other, so d = Rmeas ÷ (2 × ρ20 × kT ÷ 1000). It assumes both conductors are the same size and ignores transformer primaries between the CCR and the fault, so treat it as a starting point. In the worked example, a reading of 0.9 Ω gives a short about 218 m away.
It splits the suspect stretch of the circuit in half at each test, so the faulty section is found in the fewest isolations. The number of tests is ⌈log2 n⌉, so 100 fixtures need at most 7 tests. Number the fixtures along the loop from the CCR. The planner does not depend on the symptoms or readings.
No. The ranking is a rule-based weighing of the evidence you enter, not a diagnosis, and findings must be confirmed by testing on site. The tool does not replace fault-finding procedures, manufacturer guidance or the judgement of a qualified AGL technician. It cannot see faults the inputs do not describe, and it does not model transformer secondaries, reactance or cable capacitance.
Please read before relying on any content on this page or on any result or record produced by it.