What are CCR contactors and bypass?
The contactor that switches the regulator on and off, and the interlocked bypass path around it.
A CCR contactor is an electrically operated switch that connects the regulator input to the supply when it is commanded to. It is how the control system, locally or from the ALCMS, switches a circuit on and off, and it can drop the regulator out when a protection operates. Where one is provided, a bypass is a manual path around the contactor, used to run or feed the regulator locally while the contactor is tested or serviced. It is interlocked so that only one path is closed at a time.
The regulator output is a constant-current source, so opening a live series circuit can drive a dangerously high voltage across the break. The regulator must be switched off, isolated, locked out and proved dead before the loop or its connectors are touched. Contacts that weld closed, a coil that fails, or a bypass left in the wrong position can leave a regulator running with the control system unable to stop it.
- Identify the arrangement. Read the drawings and the manual to see which path is normal and what the bypass does on this make of CCR.
- Switch off from control. Command the circuit off and confirm the current and the lights have gone.
- Isolate and lock out. Follow the permit-to-work procedure and apply your own lock and tag.
- Prove dead. Test the CCR input and output with a proved instrument before touching anything.
- Inspect and test. Check the contactor contacts, coil and operation, and check that the bypass interlock works.
- Restore. Return the bypass to its normal position, remove the locks, switch on and check the current on the intensity steps and the status on the ALCMS.
Frequently Asked Questions
Q1What does a CCR contactor do?
A contactor is an electrically operated switch that connects the regulator input to the supply when it is commanded to. It is how the control system, locally or from the ALCMS, switches a circuit on and off, and it can also drop the regulator out when a protection operates.
Q2What is a CCR bypass?
Where provided, a bypass is a manually operated path around the contactor. It is used to run or keep the regulator fed locally, for example while the contactor is tested or serviced. It is interlocked so that only one path is closed at a time. Whether a bypass is provided, and what it bypasses, depends on the regulator make and the design.
Q3Why must a live series circuit never be opened?
The regulator output is a constant-current source, so opening the loop while it is energised can drive a dangerously high voltage across the break. The regulator must be switched off, isolated, locked out and proved dead before the loop or its connectors are touched.
Q4What goes wrong with contactors and bypasses?
Contacts wear or weld closed so the regulator cannot be switched off from control, coils fail or chatter on a low supply, and a bypass is left in the wrong position so the regulator runs with the control system unable to stop it. An interlock that has been defeated removes the safety it was fitted for.
Q5How are contactors and bypasses maintained safely?
Switch the regulator off from control, isolate and lock out under the permit-to-work procedure, prove the input and output dead, then inspect and test the contactor and the bypass interlock. Return the bypass to its normal position before restoring the circuit, and follow the manufacturer's manual.
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