Cable Lug
A cable lug is a terminal crimped onto the end of a conductor that offers a flat drilled surface for connection to a bolted point. It is used at high-current points such as battery posts, chassis bolts, contactors and shunt connections. It is sized according to the cross-section and the bolt diameter.
The job of the lug is to transfer the current from the cable cross-section to the bolt surface without loss. This requires two contact qualities at once: the crimp between cable and lug, and the bolt clamping between lug and surface.
- Crimping: it is done with a hydraulic or mechanical lug press, using the die matching the cross-section. Flattening it with a hammer or pliers does not produce a gas-tight joint.
- Surface preparation: paint, rust and the oxide layer on the contact surface are cleaned off; on an aluminium surface the oxide film is also scraped away.
- Tightening: follow the torque given by the manufacturer and use a torque wrench. Check the connection once more and re-tighten it between the first 24 hours and one week.
An extra resistance of 10 mΩ in a high-current lug connection means a 0.5 V drop and 25 W of heat at 50 A; that is enough to heat the terminal until it darkens. Verifying the connection by measuring the voltage drop under load is far more reliable than looking at it.
The context in which this term is used: Installation, redundancy and field continuity