_A_-board, all subscribers' calls being
handled through outgoing trunk jacks connected by trunks to _B_-boards
in the same as well as other offices. In these partial multiple
_A_-boards, the answering jacks are multipled a few times, usually
twice, so that calls on each line may be answered from more than one
position. This multipling of answering jacks does not in any way take
the place of the regular multipling in full multiple boards, since in no
case are the calls completed through the multiple jacks. It is done
merely for the purpose of contributing to team work between the
operators.

A portion of such a partial multiple _A_-board is shown in Fig. 379.
This view shows slightly more than one section, and the regular
answering jacks and lamps may be seen at the bottom of the jack space
just above the plugs. Above these are placed the outgoing trunk jacks,
those that are in use being indicated with white designation strips.
Above the outgoing trunk jacks are placed the multiples of the answering
jacks, these not being provided with lamps.

The partial multiple _A_-section of Fig. 379 is a portion of the
switchboard equipment of the same office to which the trunking section
shown in Fig. 378 belongs. That this is a large multiple board may be
gathered from the number of multiple jacks in the trunking section,
8,400 being installed with room for 10,500. That the board is a portion
of an equipment belonging to an exchange of enormous proportions may be
gathered from the number of outgoing trunk jacks shown in the _A_-board,
and in the great number of order-wire keys shown between each of the
sets of regular cord-circuit keys. The switchboards illustrated in these
two figures are those of one of the large offices of the New York
Telephone Company on Manhattan Island, and the photographs were taken
especially for this work by the Western Electric Company.

=Cable Color Code.= A great part of the wiring of switchboards
requires to be done with insulated wires grouped into cables.
In the wiring of manual switchboards as described in the seven
preceding chapters, and of automatic and automanual systems and
of private branch-exchange and intercommunicating systems
described in succeeding chapters, cables formed as follows are
widely used:

Tinned soft copper wires, usually of No. 22 or No. 24 B. & S.
gauge, are insulated, first with two coverings of silk, then
with one c