What is a transformer pit?
A transformer pit is the below-ground housing beside a light that holds its series isolation transformer. It keeps the transformer dry and protected, passes the primary cable through, and feeds a short secondary cable up to the fitting.
A transformer pit is the below-ground housing that holds a series isolation transformer beside the light it feeds. On a series circuit the primary cable runs from light to light in a single loop, so each pit has the cable coming in and going out, with the transformer’s primary connected in series with it through its primary connectors. The transformer then feeds the light fitting through a short secondary cable.
The pit protects the transformer and connectors from water, traffic and damage, while keeping them reachable for testing and replacement. The cover sits at finished ground level, the pit is built on a drainage layer so water does not stand around the insulation, and cables enter through ducts. Enough cable slack is left so the transformer can be lifted out without disturbing the circuit. For in-pavement lights the transformer is often housed in or next to the light’s base can instead, depending on the design. Treat a circuit as live until it has been isolated and made safe under site procedures; breaking a series circuit can be hazardous.
Frequently Asked Questions
Q1What is a transformer pit in AGL?
A below-ground housing that holds a series isolation transformer and its connectors beside the light it feeds. It protects them from water, traffic and damage while keeping them reachable for testing and replacement.
Q2How do the cables connect inside a transformer pit?
The series circuit’s primary cable enters and leaves the pit through ducts and connects to the transformer’s primary connectors, so the circuit runs through the pit in series. A short secondary cable then runs from the transformer to the light fitting.
Q3Why does a transformer pit need drainage?
Water standing around the transformer and its connectors can degrade insulation, so pits are normally built with a drainage layer, such as gravel, under the base and a cover that sheds water.
Q4Is it safe to open a transformer pit on a live circuit?
Treat the circuit as live until it has been isolated and made safe under your site procedures. Series circuits carry a constant current, and breaking the primary or secondary path can be hazardous.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.