What is a sign transformer?
The link between the series loop and one sign. Its primary sits in the loop, its secondary feeds the sign, and the two are kept electrically apart.
A sign cannot be wired straight into a series loop. The loop carries a constant current at high voltage, and the sign needs a supply of its own. The isolation transformer between them solves both: it passes the power across and keeps the two sides apart.
1Primary in the loop
The transformer's primary winding is a link in the series loop, so the circuit current flows through it in turn with every other light. Its leads are joined to the loop through sealed connectors, so the transformer can be disconnected, tested or replaced without re-jointing the main cable.
2Secondary to one sign
The secondary winding feeds only this sign, through a short cable. Energy crosses magnetically, with no direct electrical path between the windings, so the sign is isolated from the loop. If the sign or its secondary cable is disconnected, the primary loop stays closed and the other lights stay on.
3Sized to the sign
Transformers are made in set rated powers, and the sign's load, its LED module and driver, should sit within the rating chosen. A larger or double-faced sign draws more. Every sign's load also adds to the circuit total that the CCR has to supply. Isolate and make the circuit safe under site procedures before any work, because unplugging a primary connector opens the loop and the secondary should be treated as live. A sign left with an open secondary raises the primary voltage and heats the transformer, so repair it promptly.
| Element | Detail |
|---|---|
| Primary side | In series with the loop, carrying the circuit current |
| Secondary side | To one sign only, through a short cable |
| Coupling | Magnetic, with no direct electrical path between the windings |
| Current ratio | Commonly 1:1, for example 6.6 A : 6.6 A |
| Rating | Set size of rated power, covering the sign load |
| Connection | Sealed connectors, so it can be tested or replaced without re-jointing the loop |
Frequently Asked Questions
Q1What is a sign transformer?
A series isolation transformer that connects one sign to the airfield series circuit. Its primary winding is a link in the loop and its secondary feeds only that sign.
Q2Why is the sign isolated from the loop?
The transformer passes energy to the sign magnetically, with no direct electrical path from the primary to the secondary. The sign is kept apart from the series circuit, and the primary loop stays closed if the sign or its secondary cable is disconnected.
Q3How is a sign transformer chosen?
By rated power. Transformers come in set sizes, and the sign's load, meaning its LED module and driver, should sit within the rating chosen. Larger or double-faced signs draw more. The CCR must also carry the sum of every transformer's load on the circuit.
Q4Is it safe to unplug a sign transformer?
Not without isolating the circuit first. The primary connectors are in the series loop, so unplugging one opens the loop and stops every light on it, and the secondary should be treated as live. Isolate and make the circuit safe under site procedures before any work.
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