How is a cable lug crimped correctly?
The lug is chosen in the size matching the cross-section and crimped with a die-type crimping tool; flattening it with long-nose or ordinary pliers does not give a valid connection. The insulation is stripped by the length of the lug barrel; the dimension varies with the lug type. The strands sit fully in the lug without being twisted, and after crimping the cable is tested by pulling it. Verification is measurement under load: a drop of more than 0.2 V across the lug is not acceptable.
The quality of a crimped connection depends entirely on the match between tool and size. In order:
- Size: choose the lug according to the conductor cross-section. An oversized lug does not grip the strands fully when crimped, an undersized one cuts them.
- Stripping: strip the insulation by the length of the lug barrel; the dimension varies with the lug type, so determine it by holding the barrel against the cable and marking it. Do not cut strands while stripping; every broken strand lowers the current capacity.
- Insertion: push the strands into the lug without twisting them, all the strands must be inside the barrel and none left outside.
- Crimping: use a die-type crimping tool suited to the lug type. A ratchet tool is preferred because it does not release until the crimp is complete.
- Test: pull the cable by hand, there must be no movement. Then protect it against moisture and vibration with heat-shrink tubing.
On a bolted connection the tightening torque varies with the lug and terminal manufacturer; follow the torque given by the manufacturer and use a torque wrench. Over-tightening makes the copper lug flow and loosens the connection over time. Re-tighten the connection between the first 24 hours and one week after installation, then measure the voltage drop under load: below 0.2 V is good, above 0.5 V means a fault.
The full topic: Installation, redundancy and field continuity