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Peter Walsh, PE
Manufacturers are refining the older technology of MC fittings to achieve economy and simplification. This is because of the increasing usage of MC cabling versus pipe and wire.
The traditional MC fitting was constructed of expensive steel or malleable iron. It had a one end-stop design and a limited wire application for each model number. The older design was good enough for traditional installations where MC cables were specified. However, new designs were necessary to reduce installation costs for common everyday use of MC cable.
In recent years the National Electrical Code encouraged more use of MC cable by permitting new installation methods. Now MC cable is more competitive with cables installed in pipe. MC cables cost more but the labor is less with MC systems. Electrical contractors have switched over to using MC cable in many projects because the total cost is less.
One company, Arlington industries, has redesigned their MC fittings for the cost competitive high use applications. Instead of steel or malleable iron, they use economical die cast zinc fittings. Instead of a traditional limited range of cable for each model, they have designed their fittings to accommodate a wider range of wire sizes through an interchangeable end stop.
For example, a 2-inch knockout unit can serve cables with diameters from 1.7 to 2.2 inches with an internal wire bundle diameter from1.55 to 2.05 inches. That means this one unit can furnish the correct fitting from a 4/0-4 to a 500-3 wire bundle. That's six wire sizes with only one catalog number. This is possible using interchangeable end stops within the same fitting.
Photo courtesy of Arlington Industries
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