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BELL SYS TEM PRACTICES
AT &TCo Standard
SECTION 51 8-410-300
Issue 3, December 1972
6A KEY TELEPHONE SYSTEM
SELECTOR ONLY A R R AN G E MEN T
MAINTENANCE
CONTENTS PAGE
1. INTR ODUCTION
2. GENERAL
3. LINE SEIZURE, Fig. 1 4
4. BASIC OPERA iON OF SELECTOR CIRCUIT,Fig. 2 . . • • . • • • . • . 5
5. STA iON SELECTION, DIALING SINGLE-DIGIT
CODE . • • . • . • . 6
6. S TAT IO N SELECT ION , DIALING 2-DIGIT
CO DE, Fig. 3 . . . . . . . . 7
7. STATION SELECTION, USING SIGNAL KEY
7
8. TA LKING PA TH, Fig. 4 9
9. AUDIBLE SIGNALS, Fig. 5 10
10 . VISUAL SIGNA LS, Fig. 6 13
11. PRESET CONFERENCE, Fig. 7 14
12 . A DD-O N CONFERENCING, Fig. 8 17
13 . OA=-PREMISE STATION, LINE SEIZURE, Fig. 9
• . . • . • . . . • 19
14. OFF-PREMIS E STATION, INCOMING CAL L,
Fig. 10 20
15. OFF-PREMISE STATION, ANSWERING
INCOMING CALL, Fig. 11 . • . 22
1. INTRODU CTION
1.01 Th is section covers the maintenance of the
selec tor only arrangement of the 6A K eyTe lephone System, the use of sequence ch arts andopera tional sketches, and a description of th e
symbols used.
2. GENERAL
2.01 Th is section is reissued to updat e sequenc e
charts an d operational sketches .
2.02 This issue of the se ction is b as ed on CD-
an d SD-69286-01, Issue 8D. If th is sectio n
is to be used with equipm ent or apparatus reflecting a later is sue of th e draw in g, reference shoul d bemad e to the later CD and SD to determine the extent of the ch anges and the m anner in which the section may be affected.
2.03 The circuits used in the
6AKey TelephoneSystem have been reduced to simplified
sequen ce charts and operational sketches.
• Sequence charts cover the op era t ion andre lease of relays, ke ys, and ot her appara tus
in th ei r relative time order. They ar eshown from th e top downward an d ar e co nnected by appro priate lines to sho w the
interdependence of the successiv e operations.
• Operational sketches show complete circuits
fro m battery to g roun d in simplified for m ,completely disregardin g boundaries ofco nventional SD drawings. Key telephon e
unit numbers beneath the co mplete circuit
id en tify key te lephone units in which theindividual relays, relay contacts , or otherap paratus ar e located.
@ Amer ican Telephone and Telegraph Company, 1972
Pr inted in U.S.A. Pa ge 1
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SECTION 518-410 -3 00
USE OF SEQUENCE CHARTS AND OPERATIONAL
SKETCHES
2 .0 4 Afte r it has been determined that th e trouble
is in the 6A equipmen t, proceed as follows:
• W at ch relay op era t ion of equipment andco mpa re it to that of th e seque nce ch arts
as show n on the various figures.
• W he re circuit failure occurs, the ope rationa lsk e tc h e i ther will show the com plete path
for the circuit tha t failed or it will re fer to
th e figure where th e complete path may be
found.
2 .05 The fo llowing are sa m pl es of some of the
symbols used in th e preparation of the seq uence charts and op erational sketches contained
in this practice.
SEQUENCE CHART SYMBOLS
t
t_L
T
f: y·
Page 2
Relay or other apparatus
in a fully op erated posi
tion.
Relay or other ap paratus
in an unoperated or nor
mal position.
Ti me de la y circui t (time
will be designated).
Operation of relay A
causes the op era t ion of
relay B
Both relay s A an d B hav e
to be operate d before re
la y C can operate .
O p era t io n of either theA or B relay will cause
the ope ration of re la y C.
®__l_®
Y' H
B
D
Option: R el ay A, in op
erating, operates rela y
B or C de pe nding on the
wiring option prov ided .
Relay B or C in operating
wo uld in turn op erate re
lay D.
Both relays A an d B must
operate before re lay D
ca n operate. The arrow
is used to ind icate one
w ay action. In this illus
tration, relay C operate s
from relay A only.
OPERATION AL SKETCH SYMBOLS
--o-
X
Relay core an d winding.
A pp aratus oper ated (keys,
telephon e sets , etc).
A pparatus norm al. (keys ,
te lephone sets, etc).
Make contac t of an op er
ated w ire-spring-type re
lay . Relay will be desig
na ted above and contact
nu mber below. The posi
ti on of the number ind i
cates the location of the
fixed contact in the cir
cu it.
Make co ntact of an oper
ated relay having a top
an d bo ttom pile up . Re-
lay w il l be de signated
above and a contact num
ber on each side. Lette r
T or B would indicate
that the contacts are in
the top or bo ttom pile up,
respectively.
N orma ll y closed ·c ontact
of an unoperated wire
spring-type re lay. Rel ay
will be designated above
and contact number be
low.
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Normally closed contact
Aof an unoperated relay
I 12 T having a top and bottompile up. Relay will be
designated above and a
contact number on eachside.
2 : ~ Battery symbol.
•I Ground symbol.
TS Point of termination, ter-B
---e-minal strip B, terminal 19.
2.06 A description of the operation, supplementingthe sequence charts, is provided to specify
the functions of the equipment.
2.07 General maintenance of telephone sets, dials,keys, relays, power plants, etc, used with
ISS 3, SECTION 518-410-300
the 6A Key Telephone System is no t covered inthis section. References should be made to the
sections pertaini ng to these specific items.
2.08 The following wiring options are applicable
to thi s section.
WIRING OPTION
XWithout Transfer Circuit (max nine
codes)
w With Transfer Circuit (over nine codes)
HUnder 40 Lamps on System (without
aux relay busy lamp circuit)
MOver 40 Lamps on System (with aux
relay busy lamp circuit}
RLong Line Circuit Associated with
Preset Conference Circuit
K System with Preset Conference
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SECTION 518-410-300
3. LINE SEIZURE
3.01 The T and R leads of a 6A Key TelephoneSystem station are connected to battery and
ground through the windings of the A relay. Asa station picks up, relay A operates and causesthe operation of relay B. Relay B in operatingcauses the busy lamps, i f provided, to light steadilyat all stations.
ROH
A26V(A)
OPERATIONAL SKETCH
SEQUENCE CHART
ROH
A
B
BUSY LAMPS
AL L STATIONS
.._---207B OR c------.J ~ - - - - 2 0 7 B O R C - - - - - - - - - - ~
B
BUSY LAMPS
ALL STATIONS
Page 4
26V(B)
~ - - - - - - - - - - - 2 0 7 B O R C - - - - - - - - - - - - - - . J
(SEE FIG.6)
Fig. 1-Line Seizure
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ISS 3, SECTION 518-410-300
4. BASIC OPERATION OF SELECTOR CIRCUIT S EQ UENCE CHART !SEE NOTE!
4.01 Relays A and Bhave previously been operated
as described in 3. As each digit is dialed,
relay A releases and reoperates in unison wi th
the d ia l pulses. Slow release relay B remainsope rated during dialing. As the A relay pulses, a
ground is connected to th e ro tary magnet causin g
th e selector switch to step in unison wi th the dialed
pulses.
4. 02 A slow re leas ing relay C operates on the
first release o f relay A and rem ai ns operated
during the pul se train. This rela y causes operation
of the T relay whi ch in turn connect s a resistor
and capacitor across its winding. The capacitor is
charged during puls ing, and it s discharg e after
the release of re la y C holds the T re lay operatedfor appro x im ately 1-1/2 seco nd s, thus providin g
the timing interval used to cont ro l the au dib le
signal to the called station.
FIRST DIAL _IPULSE--,
SELECTOR
SWITCH
(STEPS TO
CON TACT ll
OFF-NORMAL
CONTACTS
INTERMEDIATE
DIAL PULSES
1
A
ROTARYMAGNET
ROTARY
MA GNET
A
ROTARY
MAG NET
c
T
SELECTOR SWITCH
(STEPS TO NEXT SUCCEEDIN G
CONTACT FOR EACH OPERATION
OF ROTARY MAGNET
A
ROTARYMAGNET
SELECTOR
SWITCH(STEPS TOCONTACT I)
OFF-NORMALCONTACTS
c
T
NOTE:
COMPLETION OFPULSE TRAIN
OPERATIONAL SKETCH (SEENOTEI
26V(B )
26V(B l
26 V(Bl
1---- - - -2078 OR C - - - - - - ~
~ - - - - 2078 OR C - - - - ~TS
B
ROT.
MAG
TS
B
le-------2078 OR C - - - - - - ~SEL ECTOR OPERATION IS DIFFERENT WHEN A "TOUCH-TONE" ADAPTER
IS IN THE SYSTEM AND A "TOUCH-TONE" DIAL INTER C OM STATION
ORIGINATES A CALL.
Fig. 2-Basic Operation of Selector Circuit Using Ro tary Dial
(TO FIG. 3, 7, 10 )OR PART 5.
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8. TALKING PATH
8.01 The calling station has selected and signaled
the called station as described in 5, 6, or
7.
8.02 The called station responds to the audiblesignal and connects its telephone circuit to
the T and R leads. Both stations are now connectedto a common T and R path with talking battery
being supplied through the windings of the A relay.
SEQUENCE CHART
ROH CALLING STATION
l ALLEDI TATION ANSWERS
OPERATIONAL SKETCH
ROH CALLING STATION
ANSWERSALLED STATION t
26 V(A)
NOTE: AS THE CALLED STATION
ANSWERS, IT IS BRIDGED TO THE
CALLING STATION AT THE
"A" RELAY
CALLING STA
CALLED STA
'-1•-- 20 7 B OR C ------.j j . -TEL SETS --I
Fig. 4-Talking Path
ISS 3, SECTION 518-410-300
~ - - - - - 2 0 7 B O R C - - - - - - ~
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SECTION 518-410-300
9. AUDIBLE SIGNALS
9.01 A separate signal pair is required to operatethe audible signal.
DIALING SINGLE-DIGIT CODE
9.02 The release of relay C (as described in 5)
connects audible signal power to the calledstat ion's audible signal: under control of relay in
the selector circuit, the second bank of the selectorswitch, and all normal TR relays (i f provided).
DIALING 2-DIGIT CODE
9.03 The release of relay C at the end of the
second digit (as described in 6) connectsaudible signal power to the called station's audiblesignal: under control of relays in the selector
circuit, the second bank of the selector switch,and the operated TR relay.
SEQUENCE CHART
Page 10
DIALING SINGLE DIGIT CODE
TO PART 5. {SEQUENCE CHART)
II
nAUDSIGCALLEDI STATION
II
TO PART 5. (SEQUENCE CHART)
DIALING 2-0IGIT CODE
TO FIG. 3 TO FIG. 3
AUO SIGCALLED
STATION
I-t-c
TO FIG. 3
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AUD SIG
PO W ER
SUPPLY
X OPTION
OPERATIONAL SKET C H
B
36,37
OR38
RGI
207 8 OR C - - - - - - - - - - - - ~ 1- 2078 OR C ---1
TOPA RT
5 (S EQUENCE)
I CH ART
I
II
1 CALLED W OPTIO N SE E TABLE Bn AUDSIG
I STATION
I D IALING SINGLE DIGIT CODE
TOPART 5
(SE QUENCE)
CHART AU D SIG
POWER
SUP PLY COL A COL B COLC
( . . . . - - - - - - - - - 207 6 OR C _________ ..,,__ ___ ST 216A-----
AUD SIG
PO WERSUPPLY
TS TS STATIONL R G ~ ~ · · ~ 6,37,OR 38
1- -- 207 6 OR c--f
TR TR
CO L C COL B CO L 1'- - - -S E E TABLE C __JJ
--- -TWO 216A P ROVIDED
COR R
'-""""---- 3RD 216A -- -- -. 1<1-- -- -- 2ND 216A - - - - - .
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ISS 3, SECTION 518-410-300
10. VISUAL SIGNALS SEQUENCE CHART
10.01 Relays A an d B operate on pickup as
described in 3. The operation of the Brelay closes the lamp battery supply path to lightthe busy lamps at all associated stations.
ROH
® t:®~
MS
BUSY LAMPSALL STATIONS
ROH
B (SEE FIG. I)
At (SEE FIG. I)
@ ® LAMP__ ., POWER
BUSY LAMPS
ALL STATIONS
TABLE E
COL A COL B
TERM. OPR CONT
211 8
27 6
29 10
30 II
SUPPLY
LAMP
26 V
(B)
POWERSUPPLY
COL C
TERM.
23
26
37
39
LAMPS BUSY LAMPSTATIONS ALL STATIONS
OPERATIONAL SKETCH
H OPTION (WITHOUT AUX RE L BUSY LP CKT)
1 - - - - 2078 OR C -------+1 1---- 2 0 7 B O R C ~
M OPTION (WITH AUX REL BUSY LP CKT)
8
\--------111
I + - - 2.27A OR B - - - - ~ t - - - - - - 2 . 0 7 B OR C - - - ~
TABLE E TABLE EBUSY
TABLE ECOL A
MS COL CLAMPS COLD
LG
f----0 )( OL X LG O IllTABLE E
COL B
I• 227A OR 8 ~ 2 2 7 A OR B-- . j
COL D
TERM.
34
35
36
38
Fig. ~ V i s u a l Signals
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SECTION 518-410-300
11. PRESET CONFERENCE
11.01 A preset conference can be es tablished by
di aling a code or by the u se of a s ignal
key.
11.02 Afte r line seizure has been accomplished,
as describe d in 3, a ground is connected
to the preset conference circuit under control of
the selector circuit i f the dial was used or under
control of an operated s ignal key. This ground
will cause the operation of relay ROJ, un der control
of either the PC J or PC2 re lay . In operating,
the ROJ relay co nnects battery to the PC J and
PC2 relays and locks up under their control .
11.03 The PC l or PC2 relay will now operate .
Th e operation of the PCl or PC2 relay will:
(a) lockup, (b) release the RO l re lay, and (c) connect
audible signal powe r to a maximum of six on-premise
station audible signals. When off-premise station s
(m a x imu m of three) are to be included in the
preset conference, they must be connected to
punchings 1, 2, or 3 of the PCl re lay. When th e
PCJ relay operates as described above, a groun dis supplied to operate the lo ng line circuit.
11.04 When the dial is used, the T relay in the
selector circuit releases at the en d of th e
nominal1-1/2 second interval. The release of relay
T releases th e PCl or PC2 re lay, as th e case m ay
be , thus openin g the au dible s ignal path to the
called stations. With the us e of a signal key, th e
au dible s ignal at the called stations will operate
as long as the key is depressed.
SEQUENCE CHART
Page 14
COMPLETION OF
PULSE TRAIN (SEE FIG . 2)
SIGNAL
KEY ROTARY
SEE F IG .IO \
~ ® t225A)
AUO SIGOFF-PREM
STATION
SIGNAL
KEY
AUO SIG ®+OFF-PREMSTATION
R
(225Al
ROI
PCIOR
PC2
AUO SIG
ON-PREMSTATIONS
AU O SIGON-PREM
STATIONS
MAGNET
1-1/2 SEC
T
RELEASE
MAGNET
SELECTOR
SWITCH
OFF-NORMAL
CONTACTS
RELEASEMAGNET
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SIGNALKEY
ROI
CONT ABOVE
COMPL ET ION OF PULSE TR AIN (SEE F IG. 2)
ROTARYMAGNET
26V(B )
OPE RAT IONAL SK ETC H
OPERATE PATH ROI RELAY ~ ! B l 1 1® ROI
j t -- 1ST 216A --t t+l•-- 2ND 216A--+-----3RD 216A---.-I .j.lt-217A
B
I)
TSB
SIGNALB KEY
>--<
SEE TABLE F
PC I ROI
- - - - 2078 OR C -- --- --.-. jo i----2 17 A OR 8-----1
R OI
CONT FROM BE LOW
PC IOR
PC2
CON T ABOVE
2 6 V( B )
2 6 V( 8 )
OPERATE PATH PCI OR PC2 REL AY
26Vf----,
0.
( 8) 1
2 9 l - - - * '
f- -- I ST 216 A ... -- 2ND 216 A -- •f4•>-- --- 3 RO 2 16A --- -<•+ • 17.4-0R-a-1
•I
SIGNALK EY ~
I !
PC I
.------ -- 2 07 8 OR C OR 8 -----1
L OC KUP PATH PCI OR PC2 REL A YAFTER RE L AY RO I RE LE ASES
f---•sT 216A 2N D 216 A t l• 3RD 2 16A ----<•* • 2 1 AO B-. j
SIGNAL
B KEY~>----<
..-..--- -- -- 207 8 OR C - - - - - ~ 2 1 7 A OR a-- J
CONT FROM BELOW
~ .._ __ ,
R( 225A)
A UO SIG ON- PR EMSTATION
SI GNA L
K EY
®R
( 22 5 A )
AUD S IGOFF-PREM S TAT I ON
®
AUD S I GON - PREMSTATIONS
PC IORPC2
AUD SPOWESUPPL
AUO S
POWERSUPPL
I - 1 2S
T
RE L EAMAG NE
SE L E
SW I T
OFF -
CON T
RELE
MAG N
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12. ADD-ON CONFERENCING
12.01 The incoming central office or PBX lin
picked up un der control o f an associ
key telephone system or key equipment line cir
When i t is ascertained that one of th e 6A st at
is to be conferenced with this call, a hold is pl
on the central office or PBX line.
12. 02 Th e 6A station to be conferenced is selec
signaled, and a talk ing path establishe
previously described.
12.03 The operation of th e add-on signal ke
the control station causes the operatio
relay N. The N relay in operating: (a) locks
under control of th e selector circuit, (b) opens
operate path of any other N relay, thus preventhe intercon nection of tw o or more outside l
(see inset on operational sketch), and (c) brid
the incoming central office or PBX line an d
6A st ation through the 120 F repea t coil.
12.04 The add-on conference con trol circu
eq uipped with A lead control.
If n add-o n signal key i s acciden
operated, stations busy on th e 6A
will be conferenced with th e cen
office or PBX in e .
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SECTION 518-410-300
14. OFF-PREMISE STATION, INCOMING CALL
14.01 When an off-premise station is selected in
th e usual manner (by us e of dial or signal
key ), the C or S lead ground causes operation of
relay R in the long line circuit. The R relay: (a)
opens the transmission path between the off-premiseand local s ta t ions and (b) connects generator to
th e off-prem ise station 's T an d R leads operating
the audible signal .
Page 20
14.02 An off-premise station which is included in
a preset co nference arrangement has it s
lo ng line circu i t opera ted by a ground provided
from the operated PCJ relay in the preset conference
circuit.
14.03The
Rre lay will re
lease under control of
the slow release T re lay in the selector
circuit, or upon release of the signal key, re-establish ing
the transmission pat h of the off-prem ise station.
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c
SIGNALKEY
SIG
KEY
SEQUENCE CHARTSIINAL KEY COMPLETION OF (SEE FIG 21
PULSE TRAIN •
SIGKEY P ~ ~ = : T ( ~ ~ : . A
GALL 7)
*PG I
]--I:"'lsiGPRESET
GONF CALL
+Pel
ROTARYMAGNET
1-1/2 SEC
T
RELEASEMAGNET
ISS 3, SECTION 518-410-300
C ~ ~ ~ ' s ~ T ~ ~ ~ ~ ~ F (SEE FIG. 2)
SIGKEY f:UD
rSIG
SELECTORSWITCH
R
AUDSIG
A
ROT.MAG
26 V
(B )
RINGINGPOWERSUPPLY
1-112 SEC
T
SELECTORSWITCH
OFF-NORMALCONTACTS
RELEASE
MAGNET
OFF-NORMALCONTACTS
RELEASEMAGNET
OPERATIONAL SKETCH
OPERATE PATH R RELAY
TR
1---- 1ST 216A-+- 2ND 216A - -e+o t - - - -3RD 216A ----..j
B SIG KEY
•IISG X s
B @ 35,36 , PCI 1,2 ® 1• 1 1 - - + ~
R
.....___ 25 A ----j
OR 37 1,2,0R 4 OR3
f---217A OR B---1 @) I--- 225A ~TS 1ST BANKB C T OF SEL TABLE F
sw
1--- - -2078 R ( ; - - - - ~
OPERATE PATH
~ - - - 2 2 5 A - - ~ ~ . . . - - - - - - 225A - - - - - - t
TAIL£ F
2 0 1 1 . C ITll
LEAD T!IIMIIIAL
c 21
c ,.c 4At ,.c ..c 71
c ••c 91
c 101
Fig. 1G-Off-Premise Station, Incoming Call
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SECTION 518-410-300
15. OFF-PREMISE STATION, ANSWERING INCOMING
CALL
15.01 W hen an of f-p rem is e st at ion picks up in
re sp on se to an audible signa l, th e P re la y
wil l o pera te cau sing oper ation of relay C in the
lo ng line circuit . Re lay C in op erating op en s th e
au d ib le signal path for the off-pre m is e station.
Ta lki ng battery is su ppl ie d to th e ca lling s tation
fr om the A relay and to the of f-prem is e sta tion
from the Prelay.
SEQUENC E C H AR T
OFF -PREMIS E
STATION AN SW ER S
p
c
CAL LED AND CAL LING STATIONS C ONNECTE DTO T AND R LEADS
OP ER ATIONAL SKE TC H
OFF-PREMISE
STATIO N ANS WERS
p
c
CALLED AND
26 V(A )
26 V
!AI
PRIWINDING
'---- - - - ~SEC
WINDING
~ - - - 2 2 ~ A - - - -e l
I+-- 20 78 OR C -·----- 225A - - - - - 1 ~ - 2078 OR C ------1TALKING PATH
T
CA LL ING STi lTIONS OFF-PREM
CONNECTED TO TEL SET
T AND R LEAD S
Pag e 22
22 Pages
26V
(Al
A
II
PR I
WIN DING
SE CWINDING
CALLING STATIONTEL SET
t- ------- 22!:>A - - - - - - -eo !
T
TS&
- - - 2
Fig. 11-0H-Prem ise Station, Answing Incoming Call
26V
(Al
(
(
(
'
..
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