overing of cotton. The outer (cotton) insulation of
each wire is made of white or of dyed threads. If dyed, the
color either is solid red, black, blue, orange, green, brown,
or slate, or it is striped, by combining one of those colors
with white or a remaining color. The object of coloring the
wires is to enable them to be identified by sight instead of by
electrical testing.

Wires so insulated are twisted into pairs, choosing the colors
of the "line" and "mate" according to a predetermined plan. An
assortment of these pairs then is laid up spirally to form the
cable core, over which are placed certain wrappings and an
outer braid. A widely used form of switchboard cable has paper
and lead foil wrappings over the core, and the outer cotton
braid finally is treated with a fire-resisting paint.

STANDARD COLOR CODE FOR CABLES

+---------------+-------------------------------------------------+
| | MATE |
| LINE WIRE +-------+-------+-------+-----------+-------------+
| | White | Red | Black | Red-White | Black-White |
+---------------+-------+-------+-------+-----------+-------------+
| Blue | 1 | 21 | 41 | 61 | 81 |
| Orange | 2 | 22 | 42 | 62 | 82 |
| Green | 3 | 23 | 43 | 63 | 83 |
| Brown | 4 | 24 | 44 | 64 | 84 |
| Slate | 5 | 25 | 45 | 65 | 85 |
| Blue-White | 6 | 26 | 46 | 66 | 86 |
| Blue-Orange | 7 | 27 | 47 | 67 | 87 |
| Blue-Green | 8 | 28 | 48 | 68 | 88 |
| Blue-Brown | 9 | 29 | 49 | 69 | 89 |
| Blue-Slate | 10 | 30 | 50 | 70 | 90 |
| Orange-White | 11 | 31 | 51 | 71 | 91 |
| Orange-Green | 12 | 32 | 52 | 72 | 92 |
| Orange-Brown | 13 | 33 | 53 | 73 | 93 |
| Orange-Slate | 14 | 34 | 54 | 74 | 94 |
| Green-White | 15 | 35 | 55 | 75 | 95 |
| Green-Brown | 16 | 36 | 56 | 76 | 96 |
| Green-Slate