Bell System Practices 851 Guide

BEU SYSTEM PRACTICES
AT & TCo Standard
SECTION 503-601-1 01
Issue 8, February 1980
851- AND 2851- TYPE TELEPHONE SETS
IDENTIFICATION, INSTALLATION, CONNECTIONS, AND MAINTENANCE
1. GENERAL
1.01 This section contains information on the 851-
and 2851-type telephone sets.
1.02 This section is reissued to:
• Add additional ordering information
• Update dial wiring diagram information,
Fig.
27 and 29
• Add cable routing in current 851CM and
2851CM telephone sets, Fig. 30 and 31.
2. IDENTIFICATION
2.01 The 851BM (MD) or 851CM (rotary dial)
and
2851BM (MD) or 2851CM (TOUCH-TONE "'
dial) are modular telephone sets with a G15A
handset and H4DU handset cord.
2.02 The 851CM (rotary dial) and 2851CM
(TOUCH-TONE dial) codes are available as
a completely assembled telephone set or a basic
modular telephone set base.
2.03 Purpose: Provides features of a 6-button
key station (5-line pickup and hold)
at wall
installations.
2.04 Application: Used with central office or
PBX line circuits in lA, 1A1, 1A2, or 6A
key telephone systems. Both the 851- and 2851-type
sets are wired for 1A1,
1A2 , and 6A systems. For
1A KTS, internal wiring changes must be made.
2.05 Ordering Guide:
(a) Telephone Sets (Complete):
• Set, Telephone, 851CM-* (Fig. 1)
• Set, Telephone, 2851CM-* (Fig. 2)
NOTICE
Fig. 1-851-Type Telephone Set
(b) •Telephone Set Bases:
• Base, Telephone Set, 851CM
• Base, Telephone Set, 2851CM•
(c) Modular Items:
• Faceplate, 852A-*
• Faceplate, 2852A-*
Not for use or disclosure outside the
Bell System except under written agreement
Printed in U.S.A. Page 1

SECTION 503-60 1-1 01
Fig. 2-2851-Type Telephone Set
• Housing, 851A-*
• Handset, G15A-*
• Cord, Handset, H4DU-*
*Add color suffix from Table A.
(d) Options:
• Exclusion
• Buzzer
• Station Busy
• Polarity Guard
• 4A Speakerphone
• Amplifier type handsets
Page 2
• Multiline Conferencing.
(e) Replaceable Components:
• Dial, 8RA (rotary service)
• Dial, 35AF3A (TOUCH-TONE service)
• Ringer, P1B
• Key,
635A5
• Buzzer, KS-20419L1
•
812365039 (P-23F503) Key Collar
• Lamp, 51A (10V) for all key positions
• All items listed as modular.
TABLE A
COLOR ORDERING GUIDE
HOUSING, CORDS COORDINATED
AND HANDSET FACEPLATE
COLOR
SUFFIX
COLOR SUFFIX
Black
-03
Charcoal
-70
Ivory
-50
Muted Ivory
-80
Green
-51
Light Green -71
Red
-53
Muted Red
-69
Yellow
-56
Light Yellow
-72
White
-58
Light Gray -73
Light Beige
-60
Muted Beige
-75
Aqua Blue
-62
Muted Blue
-76
2.06 Design Features:
• Sets are surface mounted on wall or vertical
surface using holes for
standard outlet box
or keyhole slots.
• Handset is cradled on top, permitting on-hook
dialing when speakerphone is provided.
• All key buttons including hold can be
illuminated (lamps
are furnished except in
Hold position).
• All pickup buttons convertible to signaling.

• An access hole is provided in the P1-type
ringer for ringer bias spring adjustment .
Refer to Section 501-259-101.
rig. 3-Early Version 851-Type Telephone Set Base
(Housing Removed)
Fig. 4-Early Version 2851-Type Telephone Set Base
(Housing Removed)
ISS 8, SECTION 503-601-101
3. INSTALLATION
3.01
When mounting the 851- or 2851-type
telephone
set , select a location which provides
at least 6 inches of clearance on all sides to permit
removal of the handset, and for maintenance.
3.02 The telephone set should be mounted before
installing the modular items.
To expose
the mounting holes, the hinged chassis assembly
must
be lowered by loosening the captive screws
(Fig.
10) holding the top of the chassis. For ease
of installation the chassis assembly can be removed
from the base pan by springing the hinged brackets
sufficiently to clear the pins. The base pan can
then
be mounted directly to the wall using the
keyhole slots, or holes provided for mounting over
an electrical outlet
box.
Caution: A void damage to wall or
telephone set whenever chassis is in
lowered position.
3.03 All sets except the CM codes can be wired
using either inside wiring cable or connector
cable. When mounted over an outlet
box, bring
wiring through opening in base pan before mounting.
When exposed, bring wiring up from bottom (right
side of handset cord jack). Allow
20-22 inches of
cable inside
set for routing and terminating.
3.04 With wiring brought into set and base pan
mounted, replace chassis assembly if previously
removed, but leave in lowered position.
3.05 Where IW cable is used, prepare and route
as follows.
(1) Remove sheath to surface of outlet box or
bottom of hole in base pan, depending
on
method of wiring.
(2) Remove cable clamps. Pinch legs of clamp
from front of chassis (Fig.
13).
(3) Slip one of the clamps provided with set
around conductors approximately 9 inches
from end of sheath. Add second clamp 2 inches
above first.
(4) Form slack loop as shown in Fig. 7 or 8
and install
first clamp in hole to left of cord
jack.
Page 3

SECTION 503-601-101
8 12 1 6938 1
EXCLUSIO N
SW
IT CH
63 5A5
KEY
KS-8 1 09L2, OR
KS-2 0 4 19LI
BUZZER
Fig. 5-2851CM Telephone Set Wi th Exclusion (Housing Removed)
(5) Route cable below jack and install second
clamp in hole to left of ringer.
(6) Twist ends of conductors together and feed
through opening between dial, ringer, and
connecting blocks.
3.06 On all sets except CM codes, if the set is
served
by the connector equipped end of an
A25B connector cable, a D-180375 Kit of Parts
must be used to obtain raw-ended conductors for
termination. The mated connector and plug should
be located as shown in Fig. 9. Check that connector
and plug
do not interfere with operation of line
switch. Cable is routed and fastened in same
manner as IW cable (Fig. 7 and
8).
3.07 Check before terminating that sufficient
slack is provided to permit hinging action
of chassis assembly.
Page 4
Cable slack must be in area behind
dial and not touching ringer. Chassis
cannot be secured if slack lies between
base pan and network or base pan
and cord jack.
3.08 Since individual terminals are not designated
on
the quick-connect blocks, terminal
identification is provided on the inside of the housing
as a wiring guide (Fig.
16). Terminals 1-30 are
on the upper block and 31-54 are on the lower
block. Terminals
51-54 are spare. Use a 714B
tool to terminate conductors.
3.09 The 851CM and 2851CM telephone sets are
equipped with a KS-16671Ll connector
(Fig. 6). An A25B connector cable is required to
connect set to key equipment (Fig.
30 and 31).

ISS 8, SECTION 503-601-101
CONNECTOR
KS-16671 Ll
Fig. 6-851CM or 2851CM Telephone Set Showing KS-16671L1 Mounting Cord Connector
Note: •care must be exercised in securing
the connector cable to eliminate the possibility
of undue
strain on the conductors and to
prevent damage to
the insulation of the
conductors which could cause shorts. Plastic
tie-wraps should be used to bundle the
conductors in order to protect the leads from
being damaged when closing the hinged chassis
.•
3.10 Exclusion Switch: To provide exclusion,
install the exclusion switch assembly as
follows.
(1) With chassis in lowered position, fasten
switch assembly to line switch bracket using
screw provided in kit. Screw must be inserted
in hole from rear of bracket.
(2) Position switch assembly horizontally (Fig. 5
or 10) and fasten securely.
3.11 Polarity Guard: When required with
the 2851-type telephone set, install the
adhesive backed 819041971 (P-90D197) guard assembly
to the left-hand bracket in the position shown in
Fig. 11.
3.12 3-Type (MD) Speakerphone: These
sets are factory-wired for 3-type speakerphone
except
that the 851-type telephone set requires
the replacement of the 8RA dial with
an 8CA dial
to provide a second set of off-normal contacts (P3
and P4 leads). When replacing the dial, the adapter
brackets must be removed from the 8RA dial and
added to the
8CA dial (Fig. 12). With both the
Page 5

SECTION 503-601-101
Fig. 7 -Inside Wiring Cable, Exposed Wiring (Early
Version)
rotary and TOUCH-TONE sets, a loudspeaker and
transmitter must be installed external to the set
and wired to the 55-type control unit. The control
unit can
be located near the telephone set (Fig. 21)
or at the KTS equipment.
3.13 4A Speakerphone: If 4A speakerphone
is provided, the
223D adapter is recommended,
however, the 82-type adapter also may
be used to
interconnect
the 4A speakerphone components
[680-type
transmitter, 108-type loudspeaker set,
and the
85B1 power unit, (Fig. 22 and 23)].
3.14 For connections to the 3-type (MD) or 4A
speakerphone system, refer to the appropriate
section
in Division 512.
3.15 When an 851- or 2851-type set is multipled
with sets furnishing speakerphone features,
certain leads must
be disconnected, insulated, and
stored to avoid interference with working circuits.
The designation of leads to
be removed are as
Page 6
Fig. 8-lnside Wiring Cable, from Outlet Box (Early
Version)
follows: T1 (V-G), R1 (G-V), P3 or IT (V-BR),
P4 or IR (BR-V),
AG (V-S), and LK (S-V).
3.16 Buzzer: The KS-20419L1 buzzer is mounted
on an insulated bracket below the dial (Fig.
13). If required, an additional KS-20419L1 may
be added or the existing KS-20419L1 may be
replaced
by the KS-8109L2 buzzer (14-30 volt ac
or de) which would be mounted using both screws.
3.17 Station Busy Lamp: A 533K diode is
used to provide a station busy lamp feature
for multibutton wall telephone sets used in
1A1
and 1A2 key telephone systems.
For connection information, refer to Table
B.
3.18 Key Features.
• All pickup positions of the 635A5 key are
convertable to signaling by the removal of
the
812857738 (P-28E773) locking pins from

Fig . 9-Connector Cable and D-180375 Kit of Parts
(Early Version)
Fig. 10-Exlusion Switch Installed and Hinged Chassis
Mounting Screws (Early Version)
the positions involved and making the
necessary wiring change (Table C).
• Lamp and set wiring are provided for
illuminating all key positions, except in the
ISS 8, SECTION 503-601-101
Fig. 11-Polarity Guard Position
Fig. 12-Dial Adapter Bracket
hold position (lamp must be furnished
separately) where the associated lamp leads
are insulated and stored.
• Line appearances on the key can be rearranged
by switching
the color coded plugs on the
rear of the key or rearrangement of the
cross connections at the key equipment.
• If multiline conferencing option is provided
the 635A5 key
must be replaced with 635CF5
key, and a
2Al matrix block shall be added
to
the equipment (Table E), in place of
polarity
guard described in paragraph 3. 11.
This unit provides eight polarity guard
Page 7

SECTION 503-601-101
CABLE
CLAMP
KS-20419LI
BUZZER
Fig. 13-KS-20419l1 Buzzer Mounted on 851-Type
Telephone Set
circuits. One polarity guard circuit is
required for each line which is conferenceable
by multibutton depression. The polarity
guard is located between the station side
of the line circuit and the station cut-down
field.
3.19 Install H4DB handset cord in later production
models of
851- and 2851-type telephone sets
by inserting the end of the cord having the tapered
plug into the handset and the square end into jack
on bottom of set. Spring locking tab should face
away from wall
at bottom of set (Fig. 19).
Warning: Cord must be removed from
jack in bottom of set anytime chassis
assembly must be put in lowered
position.
3.20 When installing H4DU handsetcord in 851BM,
851CM, 2851BM, or 2851CM telephone sets,
either end of cord will fit in telephone set base
or handset. The cord should
be inserted in the
jack until cord retaining clip locks in place.
Page 8
3.21 Where conditions warrant, the G3A6, G12A,
or G15A handset supplied with these sets
can
be replaced with other types as follows:
• For impaired hearing-G6-type
• For weak speech-G7-type
• For noisy location-G8-type or D-180413.
Note: Refer to Section 501-211-102 for
connections of these handsets. An H4CJ or
equivalent handset cord must be used
on
nonmodular type handsets.
3.22 Installation of Spade-Tipped Handset
Cords in Early Production Sets
Equipped With G12A Handset (Fig. 14):
To install spade-tipped handset cord (H4CJ or
equivalent) remove J hook stayband from the cord.
Cut back and remove cord sheath to stayband
marks. Thread spade-tipped conductors through
plug, ordered separately, (spade tips must
be bent
to clear cord entrance). Pull cord until about
1/4-inch of cord sheath is in the central cavity of
the plug. Separate the conductors into two groups
and tie an overhand knot, pulling the knot to the
cord sheath. Pull cord from plug until
strain relief
position is attained
by knot entering sheath and
resting against plug. Feed spade-tipped conductors
straight through jack and connect to proper terminals.
Insert plug in jack.
3.23 Installation of Spade-Tipped Handset
Cords in 851BM, 851CM, 2851BM,
and 2851 CM Telephone Sets: To install
spade-tipped handset cord (H4CJ or equivalent)
insert J hook stayband of cord in slot provided in
base of telephone
set and terminate on appropriate
network terminals (Fig.
26, 27, 28, or 29).
3.24 To install housing.
(1) Refer to paragraph 5.05.
(2) If chassis assembly is in lowered position,
raise and fasten in place with two captive
screws.
(3) Install collar on key.
(4) Withdraw the two mounting screws until
they
are held in the housing by their threads.

840217590
PLUG
Fig. 14-lnstalling Spade-Tipped Handset Cords in
Early Production 851- and 2851- Type
Telephone Sets with G12A Handset
With both line switch plungers fully lifted, move
the housing directly into position around the
telephone set (if an exclusion switch is installed,
the left plunger will touch the exclusion switch
when the housing is about 3/8-inch from the
base). Depress both plungers to
their on-hook
position. Continue working the housing into
position against the base. Release plungers.
(5) Fasten housing in place with two captive
screws.
(6) Check complete operation of line switch and
exclusion feature.
3.25 Use Form E-5002-A or E-5002-B as a station
number card for a TOUCH-TONE station
and Form E-4203-G for rotary sets.
3.26 To Install Faceplate.
(1) Insert tabs on faceplate into slots of housing.
Use a KS-21107 type releaser or equivalent
to depress the tab of the faceplate
retainer clip
while seating the faceplate.
To insure proper
positioning of the retainer clip, raise the handle
ISS 8, SECTION S03-601-101
of the releaser well above horizontal, as shown
in Fig.
15 before withdrawing the tool.
(2) If installing 2851A faceplate (2851-type
telephone set) place station number card in
from
front of faceplate in standard manner.
(3) If installing 2852A faceplate, an 840693253
adapter (furnished) is used to retain the
station number card. Install
adapter in faceplate
with the two retaining tabs toward the top of
the faceplate. Check for proper seating of
adapter.
(
4) If the latchingcharacteristics of the 802695247
(P-269524) retainer clip is inadequate, replace
Fig. IS-Installing 851A(MD) or 852A Faceplate
3.27 The 635A5 key uses an E-5837 form (key
button designation tabs).
To install, squeeze
sides of cap to remove from key button and
insert
designation tab. When replacing cap or key button
Page 9

SECTION 503-601-1 01
make sure assembly snaps into place. If cap does
not snap in place properly,
rotate 90 degrees.
4. CONNECTIONS
4.01 For setsequipped with a 66S1-type connecting
block, terminate IW cable as shown in Fig.
26
and 27 using the terminal identification information
inside the housing as a guide in locating terminal
numbers (Fig. 16) .
Fig. 16-Connecting Block Terminal Information
4.02 All leads or straps involved in service or
option changes
are equipped with spade
tips.
If not factory terminated, leads are insulated
and stored.
4.03 For sets equipped with the KS-16671L1
connector, (Fig.
6) an A25B connector cable
is required.
4.04 Connection Index:
Table B- Connections for KTS and/or Station
Busy Lamp
Page 10
Table C-Pickup-Signal Key Conversions
Table
D-Polarity Guard Connections for
2851-Type Telephone Set [819041971
(P-90Dl97) Guard Assembly)
Table
E-2A1 Matrix Block Connections
Fig.
24-Exclusion Switch Connections
Fig.
25-Hold Lamp Connections
Fig.
26-851BT, 851B, or 851BM Telephone
Set, Connections
Fig.
27 -2851BT, 2851B, or 2851BM Telephone
Set, Connections
Fig. 28-851CM Telephone Set, Connections
Fig. 29-2851CM Telephone Set, Connections
5. MAINTENANCE
5.
01 Maintenance replacement should be limited
to the following:
• Complete telephone sets
• Modular items
• Optional items
• Replaceable components.
5.02 When dial replacement is necessary in the
851-type telephone set, use an 8RA dial for
nonspeakerphone sets and an
8CA dial for sets with
speakerphone. Remove dial by loosening adapter
mounting screws and springing dial brackets
sufficiently to release dial from locating pins.
Tran~fer adapter brackets from dial being replaced
to new dial (Fig. 12).
5.03 Maintenance of the 35-type TOUCH-TONE
dial is not recommended and the dial should
be replaced. Adapter brackets are not involved
when replacing the TOUCH-TONE dial.
5. 04 When necessary to remove housing, the
faceplate must first be removed by using a
KS-21107 type releaser or equivalent in catch in
bottom of faceplate. Housing can then be removed