3M 7010399034 Scotch Fire-Retardant Electric Arc Proofing Tape 77W, 3 in x 20 ft, White/Gray, 1 roll/carton, 10 rolls/Case

Scotch 77W is a non-adhesive tape. The intumescent elastomer backing wraps the cable but does not stick to itself, so the wrap has to be banded or secured with a glass cloth electrical tape over it. Plan on ordering that securing tape separately, because the 77W roll on its own will not stay closed.

Yes, Scotch 77W is UL Listed and compliant with RoHS 2011/65/EU. It also meets Consolidated Edison Co. Test EO-5343-14, which is the utility spec a lot of East Coast electrical contractors and utility procurement groups write into their cable-protection scope.

It is protection against collateral damage, not insulation. When a cable in a tray, duct bank, or manhole fails and arcs, the intumescent backing on the neighboring cables expands and chars, shielding them so one fault does not take out the whole bundle. You use it on cables adjacent to potential failure points, typically in vaults, manholes, and congested trays, not on every conductor in a building.

The tape is UV-resistant, so exposed runs in yards, on structures, or in open substations are within what it is built for. Thickness is 30 mil (0.76 mm) of intumescent elastomer, which is what swells and chars to shield adjacent cable when a nearby conductor faults.

It conforms well. Elongation at break is 150 percent, so the tape stretches around irregular shapes, elbows, and splice bulges and lays down close to wrinkle-free without fighting it. That stretch is also why you should not over-tension it on straight runs.

Shelf life is 1825 days, which is five years from manufacture. For MRO stockrooms and utility storerooms that keep arc proofing on hand for emergency vault work, rotate stock on a five-year cycle rather than letting cases sit indefinitely.

The tape runs light grey and is made in the United States. The grey finish is the usual identifier crews look for when they need to confirm at a glance that an existing run in a manhole is already arc proofed.