How is a cable selected?
A selection flowchart — decide the cable’s role first, then check voltage rating, conductor size, installation method and environment against the specification.
Cable selection starts with the cable’s role. A primary series-circuit cable carries the regulated circuit current around the loop, a secondary cable connects a transformer to its fixture, and an earthing conductor does a different job again. They are not interchangeable.
Every role then passes the same four checks: voltage rating, conductor size, construction for the installation method, and suitability for the environment. The result is confirmed against the specification and standard; if nothing matches, the selection is repeated.
- Define the role. Primary series loop, secondary, or earthing and bonding.
- Match the rating. Insulation and voltage rating suit the circuit.
- Size the conductor. From current, run length and acceptable voltage drop.
- Fit the route. Burial, duct or pavement sets the construction and protection.
- Check the environment. Moisture, chemicals, temperature, rodents, sunlight.
- Confirm and record. Against specification and standard; re-select if no match.
Frequently Asked Questions
Q1How is a cable selected for airfield ground lighting?
By working through a fixed order: first the cable's role (primary series circuit, secondary, or earthing), then its voltage rating, conductor size, construction for the installation method, and suitability for the environment, and finally confirming the choice against the specification and standard.
Q2Why is the role decided first?
Each role has different electrical and mechanical demands. A primary series-circuit cable carries the regulated circuit current at the circuit's insulation level, a secondary cable connects a transformer to a fixture over a short run, and an earthing conductor has a different job again. They are not interchangeable.
Q3How is the conductor size chosen?
From the circuit current, the length of the run and the voltage drop that is acceptable. By Ohm's law the cable resistance adds to the loop resistance the CCR must drive, so a longer or thinner cable raises the voltage needed to hold the same current.
Q4Does the installation method change the choice?
Yes. Direct burial, duct, and in-pavement installation place different mechanical demands on the cable, such as crushing, abrasion and pulling tension, and so call for different constructions and protection.
Q5Which environmental factors matter?
Moisture and water, chemicals such as fuel and de-icing fluids, temperature range, rodent damage, and sunlight where the cable is exposed. The jacket and insulation must suit the conditions the cable will actually see.
Q6Who confirms the final selection?
The design engineer confirms the cable against the project specification, the applicable standard and the manufacturer's data, and the chosen type, rating and size are recorded. If nothing matches, the selection is repeated.
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