We buy MC cable.

How metal-clad cable is put together

MC is a factory assembly, not a field build. Conductors are pulled into a strip of interlocked aluminium or steel armour that closes around them, with a bare or insulated equipment ground running alongside. The conductors are usually THHN or THWN, the assembly is rated 600 V, and the armour does the work conduit would otherwise do. Nothing about it is meant to be opened on site.

Because the armour is the raceway, the cable can be run exposed and fastened directly to structure, which is why it turns up in open ceilings, mechanical rooms and parking decks rather than behind drywall. Sizes run from 14 AWG branch circuits up to 1000 MCM feeders, in one, two, three and four conductor builds, and the common trade lengths are 250 feet and 500 feet. Copper is the usual conductor, with aluminium appearing in the larger feeders.

Where MC comes from in a Houston build

Tenant improvements are the steady source. A suite is gutted, the ceiling grid comes down, and the MC that fed the old lighting and receptacles is pulled out in lengths that are still good. Fit-outs in the Galleria, Greenway and Westchase produce the same thing every few months, and the contractor is left holding coils that nobody wants to pay to move to the next jobsite. Most of it is 12 and 10 AWG with the armour still straight.

New construction leaves cleaner material. Reels ordered for a floor plan that changed, full coils returned from a crew that finished a phase early, and the short pieces that stay on the cart until someone clears it out. Plant work adds its own supply: MC in a skid building, a laboratory or an analyser shelter, pulled during a retrofit and stacked by the door. Warehouse racking and mezzanine lighting are reliable too.

• Opened coils with most of the length still on them
• Half reels from a lighting or receptacle rough-in
• Full reels bought for a scope that changed
• Cut lengths from demolition and ceiling work
• Short offcuts, bagged and loose

None of this arrives sorted. A coil from a ceiling pull usually sits in the same pile as the new material from the same job, and the two are told apart by the tag and the condition of the armour.

Why the armour outranks the footage

A coil of MC with 200 feet left and intact armour is worth a review. The same length with the armour crushed, unwound or rusted through is a handling problem with copper inside. The armour is the product: once the interlock is opened, the cable cannot be dressed around a corner without the conductors abrading against the strip, and an electrician will not install it.

Look at three places. The cut end, where the interlock should still be tight and square. The bend radius, where a coil that was folded rather than coiled shows a crease. And the conductor jacket at the end, which tells you whether the cable sat in water. Missing conductors change the picture too, usually a ground pulled out for another use and never replaced.

• Interlock tight and continuous along the full length
• No crushing, kinking or creases at the bend
• Armour free of rust and white galvanic staining
• All conductors present, including the ground
• Jacket intact, with no water tracking at the cut

A coil dragged across a slab instead of carried usually shows it in the first three feet. Photograph that section.

Putting an MC lot in front of a buyer

Send the conductor size and count, the armour type, the approximate footage on each coil, and where the material has been sitting. A photograph of the cut end and one of the whole coil covers most of what a review needs, and it says more about armour condition than a written description can.

Mixed loads are normal. MC stacked with Romex and service cable from the same renovation can travel as one lot, and the material does not have to be sorted before it is offered. Say what is on the pallet, roughly how much of each, and whether a forklift can reach it where it sits.