Copper or aluminium: how to tell, and why it matters.

Aluminium weighs about a third of what copper does for the same volume, and the difference is obvious on a full reel: one person can shift an aluminium reel that would take two in copper. On a single conductor, lift one end and judge the droop. Copper feels dense and lands heavily; aluminium feels light and rings differently when struck.

At the cut, copper is a consistent red-gold across the strand bundle with a bright edge from the saw. Aluminium is bright silver when fresh and greys within hours, and its strands are softer, marking easily under a knife. Aluminium also oxidises to a white powder in damp conditions, which shows in the interstices of an old conductor.

Jacket print names the metal, and on larger sizes aluminium is marked AL and copper CU, sometimes alongside the stranding. The print also identifies constructions that are almost always aluminium in this market: URD in 2/0 and 4/0, much XHHW in large sizes, and overhead ACSR or AAAC under a code name.

A print that is silent on metal is not evidence of copper. Many older cables print only the size and the insulation. Cross-check with weight and the cut end rather than assuming, and where a reel holds several cut lengths, check each one, because mixed reels are common after a strip-out.

Aluminium and copper do not share connectors. Aluminium needs fittings listed for aluminium, often with an oxide-inhibiting compound, and it behaves differently under thermal cycling: it expands and creeps, so a termination needs the torque the fitting calls for rather than a firm hand. Direct contact between the two metals needs a connector rated for the pair.

That has consequences for re-use. A removed aluminium feeder with damaged lugs may not justify re-terminating for a small job, while the same length in copper often does. In a review, aluminium leans on metal content while copper keeps a construction premium much longer, and the gap between them widens as the sizes fall away.

A strip-out almost always produces both metals, often in the same pile. Separate what can be separated, label the reels you are sure about, and describe the rest as mixed rather than guessing. A buyer will sort a mixed lot without complaint; a buyer who finds aluminium described as copper will discount everything else on the list.

The practical test is a scratch and a lift, done once per reel and written down. It takes a minute and removes the guesswork from a list that may hold twenty reels, and it is the difference between a lot described as mixed and a lot that has to be re-sorted on the dock with a truck waiting.

• Weigh a known length. A short piece of 4/0 copper and the same length in aluminium do not feel alike, and the difference settles the question faster than any print.
• Cut one strand. Copper is red-gold through the section; aluminium is silver and softens under a knife.
• Read the print near the end, not in the middle. The metal marking is often printed close to the factory end of the run.
• Ask what the circuit did. Aluminium is common on utility service laterals and large feeders, unusual on small branch circuits.