What is electrical isolation?
Separating a CCR and series circuit from every source of energy, so the circuit cannot become live while people work.
Electrical isolation physically separates a circuit from every source of electrical energy. On an AGL circuit that means identifying every source, switching off the CCR, opening each isolation point, then proving dead and earthing before work begins.
Isolation is not the same as switching off. A switched-off CCR is still connected, and a command from the local, remote or tower position could start it again. An isolation point is a real open gap in the supply path, and lock-out tag-out then holds it open. An isolation transformer separates the fixture from the series circuit, but it does not isolate the cable loop that runs through it.
Frequently Asked Questions
Q1What is electrical isolation?
Separating a circuit or piece of equipment from every source of electrical energy, so that it cannot become live while people work on it. The separation must be a real physical gap that can be seen or verified, not just a control signal.
Q2How is isolation different from switching off?
Switching off stops the CCR from running, but the supply is still connected and a command from the local, remote or tower position could start it again. Isolation opens the supply path itself, so nothing can energise the circuit until the isolation is deliberately removed.
Q3Why can an AGL circuit have more than one isolation point?
The circuit can be fed from the incoming supply, through the CCR, and in some layouts from standby or interconnected equipment. Every source that could energise the work area has to be identified and isolated, not just the one nearest to the work.
Q4Does an isolation transformer isolate me from the series circuit?
No. It separates the fixture lamp circuit from the series circuit, but the primary cable loop still runs through the transformer connection. The series circuit must be isolated and proved dead before anyone works on the cable, the connectors or the transformer.
Q5Is the circuit safe to touch once it is isolated?
Not until it has been proved dead with an approved tester, checked on a known source before and after the test, and earthed as the procedure requires. Long cable runs can hold charge or pick up induced voltage, so isolation is the first step and testing is the proof.
Q6How does electrical isolation relate to LOTO?
Isolation is the physical step of opening the supply paths. Lock-out tag-out then secures each isolation point with a personal lock and a tag, so it cannot be reversed while work is under way.
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