Bell System Practices 568 Operation Manual

BELL SYSTEM PRACTICES
Station Op erations M anual
Station Sets
SECTION C38. 642
Issue l, May, 1961
AT&TCo Standard
TELEPHONE SETS
568 TYPES
COMMON BATTERY - CONNECTIONS
l. 00 INTRODUCTION
1. 01 This section covers connections for the 568HB telephone
set (rot ary dialing), Fig. 1, an d the 568HT telephone set
(touch-tone calling), Fig. 3.
l. 02 Tables A, B, C and D are used in conjunction with Fig. l
and 3.
2. 00 GENERAL
2. 01 The key and telephone circuit is arranged for use with 2-
and 4-wir e common battery lines. The sets a r e furnished
wired for key telephone systems using!::..._ lead control.
2. 02 These sets do not provide connections for 4-wire local
battery pri va te lines, speakerphone feature, or busy lamp
feature.
3. 00 WORKING LIMITS
Maximum connector cab le resistance per conductor:
Lamp L leads - 25 ohms
4-wir e -r elay FW lead - 50 ohms
4. 00 FW (4-WIRE) RELAY
4. 01 The FW relay switches the r ece iver from 2-wire to 4-wir e
circuitry.
• On 2-wire lines, the relay in its normal position connects
the receiver to the 425E network. The handset and net-
work function in the usual manner as a common battery
subscriber station circuit.
• On 4-wire lines, the relay operates and disconnects the
receiver from the network and connects the receiver to
the RR and R T leads. The transmitter and network
function in the usual manner as a common battery trans-
mitter circuit. The receiver leads are externally swit ched
to impedance-matching repeating coils in the associated
line circuits.
4. 02 The FW relay operates on a 20- to 26-volt de range. The
minimum operating current is 32 milliamperes. Since the
relay cove r is hermetically sealed, relay operation cannot b e
observed and the contacts cannot be adjusted. Test the relay
by making an op era tion test on both 2-wire and 4-wire lines by
Q
American Telephone and Telegraph Company, 1961
Printed in U.S. A.
Pag e l