We buy bare copper.

Grounding, bonding and the runs that carry fault current

Bare conductor does one job in a plant: it gives fault current a low-impedance path back to the source, and it holds every metallic surface at the same potential while that happens. Grounding electrode conductor ties the service to rods, plates or a building steel column. Bonding jumpers tie piping, skids, trays and equipment frames to that same system.

Because the duty is fault current rather than load current, the sizes run large. A service may use 4/0 for its grounding electrode conductor while the phase conductors are bigger still. A ground grid under a switchyard is built from a mesh of bare conductor, often welded at the crossings, and a substation upgrade produces it by the coil.

Bus bar and jumpers are the third shape. Short, thick, drilled and often tinned, they come out of switchgear, MCC lineups and panel work. Dimension matters more than weight here: a length of 1/4 by 2 inch bar is a different proposition from a coil of 2/0, and both can look similar on a scale. Measure the cross-section before describing the lot.

• Solid bare copper, 14 AWG to 4 AWG, in coils
• Stranded bare copper, 6 AWG to 4/0 and larger
• Ground grid conductor and welded mesh sections
• Bus bar, drilled and tinned, in straight lengths
• Bonding jumpers with lugs or clamps still fitted

Cleanliness decides the grade before footage does

Copper oxidises. A coil that has sat outdoors in Houston humidity goes dull brown, then green at the surface, and the green is a corrosion product rather than a defect in the metal. Light surface oxidation is normal and does not change the outcome. Heavy green patina, caked mud or standing water inside a coil does, and the middle of the coil is where to look for it.

What really costs a lot is contamination that cannot be separated. Solder, paint, tar, concrete encasement and brazing alloy all travel with the copper and have to be dealt with before it goes anywhere. A coil pulled out of a slab with concrete still clinging to it is graded as mixed recovery, not as clean bare copper.

Length barely matters by comparison. Bare copper has no installation value once it has been bent, buried or welded, so a lot is judged as metal with a shape. A coil of 4/0 dragged behind a truck is a metal lot, while a straight length of the same conductor off a bus is not, and the difference has nothing to do with footage.

Mixed copper and aluminium in one bundle should be described as mixed. Separation is part of the review, not a problem to hide.

Tinned copper and the older work it turns up in

Tinned conductor has a thin tin coating over the copper, applied so the surface resists corrosion and takes solder easily. It appears in marine and dock work, in older industrial installations, in some grounding applications and in equipment built to a specification now rarely written. A coil of it turns up at the bottom of a rack more often than anyone expects.

The coating changes how the metal is graded. Tinned copper is not the same as bare bright copper, and a lot that mixes the two is reviewed as two grades rather than one. Age matters as well: older tinned conductor can carry brittle insulation on the ends where it was terminated, and that has to be cut back.

It is still worth collecting. Tinned copper off a decommissioned dock or an old substation is ordinary material, and it usually comes in coils and straight lengths that are easy to handle. Send it described as tinned, and the review starts on the right basis rather than half a grade off. A coil that mixes tinned and bare conductor is the one case worth separating before it is offered.

Weighing a bare copper lot before it leaves

Weight is the honest measure for bare conductor, and it is the one number worth establishing before anything moves. A platform scale handles coils and short bar. A crane scale handles a grid section or a bundle too heavy to lift by hand. If neither is available, the dimensions and a count of the pieces will carry the review to the point where it can be verified.

Send the form the copper is in, the approximate dimensions or gauge, the total weight if you have it, and photographs of a representative piece rather than the whole pile. One clean shot of the metal and one of the worst section in the lot is more useful than a wide photograph where everything looks the same.

Metal content sets the floor, and that is true of every lot. What sits above the floor is the question of whether the copper is clean enough, uniform enough and large enough to be used again rather than melted. Answer that in the first message and the conversation gets short.

• Form: coil, straight length, bus bar or grid section
• Gauge or cross-section, and overall weight if known
• Bare, tinned or mixed, and how mixed
• Surface condition and any concrete, solder or paint
• Whether the pieces are one size or an assortment