Ch. XIII) INSTALLATION OF ARC LAMPS 503 one cannot make a wrong connection (fig. 268A). Such an attach¬ ment would also serve for alternating current, but is unnecessary, as it makes no difference which way the attachment is connected. The conductor from the electric supply in the outlet box to the lamp switch, if the distance is small, not over 2 to 3 meters (6 to 10 ft.), is most conveniently made of flexible cable of the proper carrying capacity (see the table of carrying capacity of flexible Fiu. 268. Separable Wall Receptacles, Polarized (/l) and Non-Polarized (B). (Cuts loaned by H. Hubbell, Inc ). With direct current, a polarized attachment insures the same polarity with¬ out attention on the part of the operator; with the non-polarizcd form there is liability of reversing the polarity unless the connections are specially marked, and care is taken in putting the separable cap in position. Either form can be used with alternating current also. electric cables). The two wires or cables are often enclosed in a common sheath. § 698. In connecting the two wires to the attachment cap, the insulation is removed for a short distance (1 to 2 cm. Y* in.), the wires scraped clean, twisted all together, and then turned to a loop to surround the set screw. Great care must be taken to avoid leaving any of the strands free; this would lessen the carrying capacity, but more important still, they might become displaced and make a short circuit (§688).