What are transformer pits?
The buried chamber that houses an isolating transformer away from the light. It is built by the civil team, but the AGL system depends on it staying dry and accessible.
A transformer pit is a buried chamber, concrete, precast or a purpose-made housing, that holds an isolating transformer and its connectors. It is used where the light sits on a shallow can and the transformer cannot go under the fixture. The primary cable runs in and out through ducts, and a short secondary cable runs to the can.
It is a civil interface because the pit is excavated, bedded and backfilled with the pavement works. Its location, depth, duct entries, drainage and lid level must be agreed with the civil team before the surface is closed, and it needs clear space around it for later access.
Separate chamber beside the light. Used with shallow cans, with a short secondary cable to the fixture.
Transformer sits inside the can directly under the light, so no separate pit is needed.
Frequently Asked Questions
Q1What is a transformer pit in airfield ground lighting?
A buried chamber, concrete, precast or a purpose-made housing, that holds an isolating transformer and its connectors away from the light fixture. It has a removable lid, cable entries and drainage.
Q2Why is a transformer pit a civil interface?
It is excavated, bedded and backfilled as part of the civil works, and it sits in or beside pavement. Its location, depth, duct entries, lid level and drainage must be agreed with the civil team before the area is closed.
Q3When is a transformer pit used instead of a deep base can?
Where the light uses a shallow can, such as many inset fixtures, the transformer cannot sit under the light. It goes in a nearby pit, and a short secondary cable runs to the can.
Q4What does the pit need for drainage?
A gravel sump or drain outlet so water does not stand around the transformer and connectors. Standing water degrades insulation and corrodes fittings.
Q5Why does the pit lid matter?
The lid gives access for inspection and replacement, and where it is trafficked it must carry the loads expected, such as vehicles or aircraft wheels. Its level should match the surrounding surface.
Q6Where are the requirements defined?
FAA AC 150/5345-42 covers transformer housings and junction boxes, and ICAO Aerodrome Design Manual Part 5 covers electrical systems. Confirm against the current edition and the manufacturer's installation data.
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