MC cable: interlocked armour and fit-out surplus

What sits under the armour

MC cable is a factory assembly: THHN or THWN conductors, a bare or insulated equipment ground, and an interlocked strip of aluminium or steel wrapped around the bundle. The strip overlaps itself in a spiral so the armour is continuous and flexible. It is not conduit. It is a listed wiring method with its own fittings, its own bend radius and its own rules about support.

Two variants show up constantly in Ohio commercial work. MC-AP uses a lighter aluminium armour and a reduced conductor set, and it is common in high-rise and institutional branch circuits where weight matters. HCF, the health-care-facility type, carries a redundant grounding path and an aluminium armour; it is specified for patient-care areas and shows up in hospital and clinic fit-outs. Both are printed along the armour with the type, the size and the listing.

Armour condition and the problem with cut lengths

A coil of MC that has been dragged across a slab will show it: flattened spirals, a strip that has opened a gap, armour twisted against its lay. A crushed or opened interlock is not cosmetic. The armour is part of the grounding path on most of these assemblies, and a gap in the spiral is a question an electrician will not answer on a used coil.

Cut lengths are the norm. Fit-out crews pull whips of six, ten and twenty-five feet from a 250-foot coil and leave the remainder coiled in the corner with a wrap of tape. That remainder is usable, but each cut end has to be dressed, and the last few feet of any coil are usually scrap because the armour has been opened and closed too many times at the same point.

Fit-out surplus in the data-centre corridor

The Licking County corridor around Newark has absorbed a great deal of data-centre and support construction, and that work changes layout late. A hall gets re-racked, a row of cabinets moves, a tenant takes more white space than the drawing allowed. What is left behind is pallets of coil ends, boxes of pre-made whips, and partial coils in the original wrap that were never opened because the circuit was deleted.

Data-centre work also produces a particular kind of surplus: matched lengths. Whips cut to a repeated length, bundled and tagged by the installing contractor, are more useful than a random coil because they can be counted rather than measured. Where those bundles exist, say so. A hundred identical whips is a different lot from a hundred feet of coil.

What a review needs

Photograph a cut end so the conductor count and the armour style are visible, then a length of armour showing the print, then the coil as it sits. If the coil is banded and still in mill wrap, that is the strongest single photograph in the set.

• Cable type as printed: MC, MC-AP or HCF
• Conductor count and size, for example 12/2 or 10/3
• Whether whips are pre-cut and bundled, and at what length
• Armour condition at the coil ends and along the outer face
• Total coil count and whether any coil is still in mill wrap