Cabling is one of the largest bulk quantities on a process plant and one of the easiest places to lose control of quality. Thousands of cables, each pulled, glanded, terminated and tested, each tagged at both ends. When controls slip, the problems surface at loop check or energization, when they are slowest and most expensive to trace. The controls below are the ones that matter most for industrial cable tray, cabling and termination work.
Cable tray installation
- Supports at the specified spacing, with tray loading checked against the design
- Segregation between power, control and instrument trays, kept at crossings too
- Bends and risers that respect the minimum bend radius of the largest cable
- Earth continuity across tray sections and bonding to the earthing system
- Covers where needed for sun or mechanical protection
- Clearance from hot surfaces, and spare capacity for future cables
Segregation is the rule that gets bent under pressure. Running an instrument cable in a power tray “just for this section” invites interference problems that are hard to diagnose later.
Use the cable schedule as a tracking tool
The cable schedule lists each cable’s tag, type, size, route, end points and length. Treat it as a live record, with status columns for pulled, glanded, terminated and tested. Drum schedules allocate cables to drums to cut waste. Check the remaining length on a drum before starting a long run, so you do not end up needing a joint.
Pulling controls
- Confirm maximum pulling tension and minimum bend radius from the manufacturer’s data
- Use rollers at bends and entry points, and never drag cable over tray edges
- Seal cut ends immediately to keep moisture out
- Leave tails long enough for termination plus a service loop
- Tag both ends straight away with the schedule tag
Test insulation resistance before termination
Test each cable’s insulation resistance after pulling and before termination. A failed cable found at this stage is simply replaced. Found after termination, it means de-terminating two ends and repeating the work. Record results against the cable tag.
Glanding
Gland type must suit the cable construction and the area classification. In hazardous areas, gland certification must match the protection concept of the enclosure it enters. Armor should be earthed through the gland where the design requires it, sealing washers fitted, and unused entries closed with certified stopping plugs.
Termination controls
| Check | Why it matters |
|---|---|
| Core markers match the termination drawing | Traceability for loop checks and future maintenance |
| Correct lug or ferrule size, properly crimped | Prevents loose connections and hot spots |
| Terminals tightened to the specified torque | Loose power terminations overheat under load |
| Screens terminated as designed, often at one end only | Avoids earth loops and signal noise |
| Spare cores terminated or insulated as specified | Keeps spares usable later |
| Final check against the termination drawing | Catches crossed cores before loop testing |
Records commissioning will ask for
Pulling, insulation resistance, glanding and termination records become part of the test pack used in pre-commissioning checks for E&I systems. Incomplete records hold up system completion even when the physical work is finished.
Many cabling problems start in design, for example trays routed after piping has filled the rack, as discussed in MEI design coordination. The wider scope is covered in electrical and instrumentation services for process plants.
Apex Core Engineering supplies electricians, instrument technicians and E&I supervisors through its skilled manpower supply service.
Frequently asked questions
Why are power and instrument cables segregated?
To limit electromagnetic interference on low-level instrument signals and to protect them from faults in power circuits.
Should instrument cable screens be earthed at both ends?
Commonly only at one end, usually the control room end, to avoid earth loops. Always follow the project’s earthing design.
When should insulation resistance be tested?
After pulling and before termination, and again during pre-commissioning.
For electricians, instrument technicians or E&I supervision on your next scope, contact Apex Core Engineering.