How short?
For a Tan Delta test the capacitance should be a minimum of 5,000pF to have enough current to run a test. To find the minimum length, divide 5,000pF by the capacitance per foot of your cable (contact manufacturer). On average, the capacitance per foot is 100pF/ft. The resulting number will give you the minimum needed to test.
Example: 5,000pF / (100pF/ft.) = 50ft. of cable.
How long?
Each unit has its own specifications so check your unit manual for its capabilities. For example, our HVA28TD can test up to approximately 5,000ft. (0.5uF) at maximum voltage and maximum frequency. Once the load exceeds that capacitance(0.5uF), the frequency will automatically drop to accommodate the load. You must pay attention to this frequency drop with Tan Delta diagnostics because you need to maintain 0.1Hz to evaluate a cable with Tan Delta.
Note: 1 mile = 5,280 ft.
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