What is circuit continuity?
The unbroken path round a series lighting loop — one break anywhere stops the current and puts every lamp out.
Circuit continuity is the unbroken, closed conductive path round a series lighting circuit. Current leaves one CCR output terminal, passes through every cable, connector and isolation transformer primary in turn, and returns to the other terminal. It flows only while that path is complete.
Because every lamp shares one series path, a break anywhere stops the current everywhere, so every lamp on the circuit goes out, not just the one at the fault. Continuity is checked with the circuit isolated, locked out and proved dead, by measuring loop resistance and comparing it with the commissioning baseline. It is different from insulation resistance, which tests leakage to earth rather than the completeness of the path.
- Isolate. CCR off, locked out and proved dead before any test lead is connected.
- Disconnect. Open the loop at the CCR output terminals.
- Measure. Read end-to-end loop resistance with a suitable low-resistance meter.
- Compare. Check the reading against the commissioning baseline.
- Locate. If it is high or open, section the loop at accessible points and test each section.
- Record. Log the result; insulation resistance is a separate test.
Frequently Asked Questions
Q1What is circuit continuity in a series lighting circuit?
The unbroken, closed conductive path round the loop: from one CCR output terminal, through every cable, connector and isolation transformer primary in turn, and back to the other terminal. Current can flow only while that path is complete.
Q2Why does one break put out every lamp on the circuit?
Because the loop is a single series path carrying one current. A break anywhere, in a cable, connector, joint or transformer primary, stops that current everywhere, so every lamp goes out, not just the one at the break.
Q3Does a failed lamp break circuit continuity?
Not by itself. Isolation transformers are designed so a failed lamp does not open the primary loop, though how this is achieved depends on the fixture and transformer design. A break in the cable, a connector, a joint or a transformer primary does open it.
Q4How is circuit continuity tested?
With the circuit isolated, locked out and proved dead, and the loop disconnected at the CCR, the end-to-end loop resistance is measured with a suitable low-resistance meter and compared with the commissioning baseline. A very high or infinite reading shows a break.
Q5How is continuity different from insulation resistance?
Continuity shows the conductor path is complete. Insulation resistance shows how well the insulation keeps current from leaking to earth. A circuit can pass one test and fail the other, so both are recorded.
Q6What commonly causes a loss of continuity?
Damaged or cut cable, a loose, corroded or water-affected connector or joint, a poorly made termination, or an open transformer primary. The break is found by sectioning the loop at accessible points and testing each section while the circuit remains isolated.
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