Cold Loop Check SOP (Continuity and Insulation)

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• Document control header (SOP COM 002)
• Purpose, scope and references
• Safety, tools and prerequisites
• Numbered step by step procedure
• Acceptance criteria and records
• Approval block for sign off

1. Purpose

To find wiring faults before energising instrument loops.

2. Scope

Instrument signal and power cables from field devices through junction boxes to marshalling cabinets.

3. References

• Loop drawings and termination schedules
• Cable schedule
• Insulation tester manual

4. Responsibilities

• Instrument technician: carries out the work and records results.
• Instrument engineer or supervisor: reviews and approves the records.
• Operations: grants the permit, isolates the process and returns the equipment to service.

5. Safety Precautions

• Work only under a valid permit to work and follow the site isolation (lockout tagout) procedure.
• Wear the PPE required for the area: safety helmet, glasses, gloves and safety shoes as a minimum.
• In hazardous areas use certified or intrinsically safe test equipment, or obtain a gas free certificate and hot work permit.
• Inform the control room before starting, and before returning the instrument to service.
• Insulation testers produce high voltage: make sure no one touches the circuit, and discharge cables after each test.
• Disconnect transmitters, I/O cards, barriers and surge protectors before testing; the test voltage can damage electronics.
• Do not use an insulation tester on IS circuits in a hazardous area without a gas free certificate.

6. Tools and Equipment

• Insulation resistance tester (500 V DC for instrument cables)
• Multimeter or continuity tester
• Radios
• Termination schedules

7. Prerequisites

• Cables installed, glanded and terminated; ferrules fitted.
• Electronic devices at both ends disconnected.

8. Procedure

8.1 Continuity and polarity

1. Short the pair at the field end.
2. Measure continuity at the marshalling end and confirm the loop resistance is reasonable for the length.
3. Remove the short and confirm open circuit; check polarity follows the drawings.

8.2 Insulation resistance

1. Test core to core, each core to screen and each core to earth at 500 V DC for one minute.
2. Record the readings; discharge the cable after each test.

8.3 Screen and earthing

1. Confirm the screen is continuous through the junction box and earthed at one end only (normally the control room).
2. Confirm the screen is isolated from earth at the field end.

8.4 Completion

1. Reconnect devices, record results and raise punch items for failures.

9. Acceptance Criteria

• Continuity and polarity as per drawings.
• Insulation resistance at or above the project requirement (commonly ≥ 100 MΩ for new instrument cables).
• Screen earthed at one point only.

10. Records

Related tools

This is a generic procedure. Adapt it to your site permit system, the manufacturer instructions and your quality system before use.

Frequently Asked Questions