What is the primary winding?
The primary is the winding connected in series with the constant-current loop. It carries the full loop current and passes energy to the secondary through the core, and a break in it takes out the whole circuit.
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Normal. The loop current flows through every turn of the primary, then through the primaries of the other transformers, each feeding its own light, and back to the CCR. The current sets up the flux that carries energy to the secondary. Every primary on the circuit carries the same current.
The primary winding is the winding of a series isolation transformer that is connected in series with the constant-current loop. It carries the full loop current, the same current as every other primary on the circuit, and that current creates the magnetic field which passes energy through the core to the secondary winding.
Because the primary is part of the loop itself, a break in it opens the whole series circuit: every light on the loop goes out, not just one. Each primary only drops a few volts (up to a few tens on larger ratings), but its insulation is rated for the high voltage of the whole loop. Treat the primary leads as live until the circuit is isolated and proved dead under site procedures; a continuity check will show an open winding, and an insulation test checks it against the core and secondary.
Frequently Asked Questions
Q1What is the primary winding in AGL?
The winding of a series isolation transformer that is connected in series with the constant-current loop. It carries the full loop current and creates the magnetic field that passes energy through the core to the secondary winding.
Q2Why does an open primary affect the whole circuit?
Because the primary is part of the loop itself. A break in it opens the series circuit, so the current stops for every light on the loop. An open secondary is different: only the one fitting goes out and the loop keeps running, although an open secondary raises the primary voltage and heats the transformer, so it should be repaired promptly.
Q3What current does the primary carry?
The loop current set by the CCR, the same current that flows through every other primary on the circuit. It changes with the brightness step, up to the top-step value, such as 6.6 A on a 6.6 A circuit or 20 A on a 20 A circuit.
Q4Is the primary voltage the same as the loop voltage?
No. Each primary drops only a few volts to a few tens of volts, roughly its fitting’s power divided by the current, and the drops of all the primaries add up to the loop voltage the CCR supplies. The insulation is rated for the high voltage of the whole loop, not only the few volts across the winding.
Q5How do I check a primary winding?
By testing with the circuit isolated and made safe under site procedures: a continuity check shows whether the winding is open, and an insulation test checks it against the core and secondary. Treat the leads as live until the circuit is proved dead.
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