Cable pulling is the stage where good cable is most often ruined. Too much tension stretches copper, tears insulation and creates hidden faults that appear months later. A pull plan, the right lubricant and a post-install test prevent most of the damage.
Quick Answer
Keep pulling tension below the cable maker's limit, usually 50 percent of the conductor strength.
Respect the minimum bend radius, often 10 times the cable diameter.
Use a compatible lubricant and pull at a steady speed.
Never pull around a sharp corner without a roller or sheave.
Test insulation resistance after every pull and before energising.
What is cable pulling?
Cable pulling is the process of drawing a cable through conduit, duct or tray using a rope, winch or pulling eye.
It means installing the cable without exceeding its tension, bend radius or sidewall pressure limits.
cable pulling in practice
Typical limits for common cable sizes:
| Cable size | Max pull tension | Min bend radius |
|---|---|---|
| 2.5 mm copper | About 250 N | 10 times diameter |
| 6 mm copper | About 600 N | 10 times diameter |
| 16 mm copper | About 1,600 N | 12 times diameter |
| 35 mm copper | About 3,500 N | 12 times diameter |
| 95 mm copper | About 9,500 N | 15 times diameter |
| 240 mm aluminium | About 12,000 N | 15 times diameter |
What does a cable pulling and testing job cost in Nigeria?
A cable pull and test for a small building costs about 150,000 to 350,000 naira in Lagos.
An industrial pull with trays and rollers runs about 500,000 to 1,500,000 naira.
Cable lubricant and pulling aids add 20,000 to 80,000 naira.
Insulation resistance testing costs about 50,000 to 120,000 naira.
Replacing a damaged cable can cost 3 to 5 times the original pull.
A winch and experienced crew add 100,000 to 300,000 naira per day.
How is cable pulling carried out?
- Plan the route and count every bend before the pull starts.
- Check the cable drum for damage and test insulation before pulling.
- Set rollers at corners and protect the cable entry and exit.
- Apply lubricant and pull steadily with a tension meter.
- Stop immediately if tension rises or the cable binds.
- Test insulation resistance and record the result before termination.
Sources
IEC 60287 cable current rating guidance, Cable maker installation manuals, IEC 60364 electrical installation rules, NIS 1000 electrical installation rules
What tension does to a cable
Copper stretches when it is pulled too hard. The conductor becomes thinner and its resistance rises.
Insulation can tear at the sheath or separate from the conductor. The damage is often invisible from outside.
A stretched cable runs hotter at the same load. That shortens life and can trip protection.
Calculating the pull
Estimate tension from cable weight, route length and friction. Add extra for every bend.
Use the maker's maximum tension, usually a share of the conductor's breaking load. Never guess from cable size alone.
For long or complex pulls, use a tension meter and a radio link between the winch and the feed end.
Bend radius and sidewall pressure
A tight bend crushes the insulation on the inside and stretches it on the outside. Both create weak points.
Sidewall pressure is the force of the cable against a sheave. Too much pressure flattens the insulation.
Use large rollers at corners and never pull around a bare conduit edge.
Lubrication and pulling speed
Use a lubricant made for the cable sheath. Oil-based grease can attack some plastics.
Pull slowly and steadily. A jerky winch shock-loads the cable far above the steady tension.
Keep the feed end attended. A cable that snags at the drum can be damaged before the winch operator notices.
Protecting the cable after the pull
Seal duct ends against water and rodents. A cable that sits in water will fail at the sheath.
Support the cable in trays at the maker's spacing. Sagging cable strains terminals.
Leave a service loop at each end, but do not coil excess cable tightly. A tight coil traps heat.
Testing and documentation
Measure insulation resistance phase to phase and phase to earth. Compare with the pre-pull reading.
A big drop from the pre-pull value means the cable was damaged. Do not energise it.
Record the test values, cable drum numbers and route. The record is your evidence if a fault appears later.
Related guides from this series
- Electrical Cable Jointing and Terminations in Nigeria
- Electrical Cable Tray and Ladder Installation in Nigeria
- Cable Derating for High Ambient Temperature
About the author
Illuminate Engineering Limited designs and installs electrical distribution systems for commercial and industrial clients in Nigeria.
Frequently Asked Questions
What is the maximum pulling tension for a cable?
Use the maker's figure, often about 50 percent of the conductor breaking load. For a 16 mm copper cable that is roughly 1,600 N.
Can I pull cable around a 90 degree bend?
Yes, with a proper sheave or roller and a bend radius above the minimum. Pulling around a bare edge damages the cable.
How do I know if a cable was damaged during pulling?
Compare insulation resistance before and after the pull. A large drop is a warning sign.
Is it safe to pull cable with a vehicle?
No. A vehicle cannot control tension and shock-loads the cable. Use a winch with a tension meter.
Conclusion
Cable pulling is a controlled operation, not a race. Tension, bend radius and lubrication decide whether the cable survives.
Plan the route, measure the pull and test afterwards. The cable will give decades of service instead of months.