Bell 501-136-100 Service Manual

BELLSYSTEM PRACTICES SECTION 501-136-100
AT&TCo Standard Issue 7, November 1979

STATION TRANSFORMERS

IDENTIFICATION

1 GENERAL unit to be in close proximity to the

1.01 This section contains information on station
transformers. 1.03 Locate transformers where they will be

1.02 This section is reissued to:

. Show KS-20426L3 transformer MD a 110- to 125-volt ac power service outlet.

• Revise Table A. _ Make sure that power service outIet

Danger: When providing power for
illuminated station sets, two or more

transformers should never feed the

same inside wiring pair. If one 1.05 To prevent accidental removal, power cords

transformer is unplugged while the may be fastened to the ac outlet with a

secondary terminals of that transformer power-cord plug-retainer assembly (Section 167-400-210)
are being energized through the inside and plug-in transformers may be secured with a

wiring, by another transformer, the clamp. A clamp is furnished with some of the
exposed terminal blades of the KS-20426L3 (MD) transformers, others have a

unplugged transformer would be molded mounting tab. A retaining clamp is available
energized with 110 to 125 volts ac. for the 85B1 and 95B1 power units. The 2012-type
Installations of multiple transformers transformer may be secured with a 2A clamp.
connected to the same inside wiring

pair should be avoided and corrected

if encountered in the field. 1.06 The B cord clip (size 1) provides a means

Warning: Care should be taken to pulled from the transformer screw terminals.

strip and dress leads connecting to

Io w voltage output terminaIs of
transformers and power unit to assure 1.07 The B cord clips come 10 to a package and

that inadvertent connection to conducting should be ordered as follows:

surfaces or other power source does
not occur. If more than one transformer 1 package (10 clips per package)--Clip, Cord,

or power unit is plugged into a multiple B1-61.

receptacle power strip, there must

be at least one inch separation
between them. Only UL listed 1.08 Remove protective paper from adhesive of

receptacle power strips with adequate B cord clip and stick clip to bottom of station

power rating shaH be used. Use of transformers as shown in Fig. 3. Terminate D

a continuous terminal power strip station wire on screw terminals of 2012-type

that allows the secondary output transformer and hook station wire through B cord

terminals of the transformer or power clip as shown in Fig. 3.

ac line source is not recommended.

accessible for inspection and maintenance.

1.04 Transformers discussed in this section require

is not under control of a switch.

of attaching D station wire to station

transformers to prevent the wire being accidentally

Not for use or disclosure outside the

Bell System except under written agreement

NOTICE

Printed in U.S.A. Page 1

SECTION 501- 136-100

2A clamp with 2012-type

transformers having folded blade
type prongs wiIl normally not be

necessary.

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FOLDED BLADE SOLID

TRANSFORMER PRONGS PRONGS

2012A 2ACLAMP

Fig. 2--2012-Type Transformer, Prongs

Fig. 1--2A Clamp

2. 2012-TYPE TRANSFORMER

Danger: For safety, securely attach
retaining clamp to ac outlet using outlet "s_"SZATiON

cover screw BEFORE attempting to install w_R__
2012-type transformer. See Fig. 1. When
removing 2012-type transformer always
unplug unit compIeteIy from outlet BEFORE

attempting to remove the retaining cIamp.
This wilI prevent the possibility of a loosened

retainer clamp or metallic outlet cover .....

making contact with the ac prongs of the
2012-type transformer when partially

withdrawn from outlet. Do not use 2A
clamp or similar retaining clamp on outlets

where cover mounting screw holds the .....

k

duplex outlet in the box. :: \

2.01 A 2A clamp may be used to secure the "\, ............ .... 2o_2-Tv:_:\

2012-type transformer to a standard electrical _'_:' CORDCL_P TRANSFORMER

service outlet (Fig. 1) in those locations where the
transformer is subject to being accidentally dislodged

from the receptacle. Fig. 3--Cord Clip Used to Secure Station Wire to

Transformer

Page 2

after April 1969 have folded blade-type

prongs (Fig. 2), which have improved

The 2012-type transformers manufactured

retaining characteristics. Use of the

ISS 7, SECTION 501-136-100

2.02 The 2A clamp is available in Light Olive TOUCH-A-MATIC 16 telephone sets, and the 55A

Gray (-49) and Ivory (-50). or 55B control unit in 3-type (MD) speakerphone

A. 2012A (MD) or 2012C Transformer or Ivory (-50). The length of wire between the

sets per residence along with one
PRINCESS _ telephone set may be __ Do not use 2012B or 2012D transformer

Any number of TRIMLINE _ telephone 100 feet of standard inside wire.

transformer. However, only one

powered from one 2012A or 2012C _ in place of a 2012.4 or 2012C Wansformer.

PRINCESS telephone set can be
connected to a 2012A or 2012C

transformer. When installing 2.10 Prongs for the primary terminals are provided
multiple PRINCESS sets use so that the transformer can be mounted in

KS-20426L3 transformer or provide a standard parallel-blade convenience receptacle.

an additional 2012A or 2012C Screw terminals are provided for secondary winding
transformer for each telephone in a recess on the same side of apparatus as the

set. prongs.

2.03 The 2012C is equivalent to and a direct 2.11 With 115 volts, 60 Hz applied to the primary

replacement for the 2012A (MD) transformer, winding, the secondary delivers approximately

2.04 The 2012A or 2012C (Fig. 4 or 6) transformer
supplies power for telephone sets with dial 2.12 A sustained short circuit across the secondary

night light feature and is available in Light Olive of the 2012D for 10 to 15 minutes will cause
Gray (-49) or Ivory (-50). the transformer to go open and remain that way.

to power 3-type (MD) speakerphone
systems or TO UCH-A-MA TIC _ 16 2.13 The 2012D transformer will be manufactured

Do not use 2012.4 or 2012C transformer transformer overheating.

telephone sets. with back plates in a contrasting color from

2.05 Prongs for the primary terminals are provided in preventing mixing and misuse with 2012A and
so that transformer can be mounted in a 2012C transformers.

standard parallel-blade convenience receptacle.
Screw terminals are provided for secondary winding
in a recess on the same side of apparatus as the

systems and is available in Light Olive Gray (-49)

transformer and the control unit should not exceed

17 volts at 0.132 amp.

This is a self-protecting fail safe feature to prevent

the case. The visual difference is provided to aid

prongs. _: _:,

2.06 With ll5-volts, 60 Hz applied to the primary ii_ii _i_,_,_i_i_i_iii?iiii_ii?F_,_ii_i

winding, the secondary winding delivers _ :_i_

approximately 7 volts at 0.250 amp. _ ii

2.07 A 25-foot telephone set mounting cord is not !ili_

recommended because the added resistance _.... ............................

of this cord results in decreased illumination.

B. 2012B (MD) or 2012D Transformer Fig. 4--2012A Transformer

2.08 The 2012D is equivalent to and a direct
replacement for the 2012B transformer. 3. KS-16886L2 TRANSFORMER

2.09 The 2012B or 2012D transformer (Fig. 5 or 3.01 The KS-16886L2 transformer (Fig. 8) is

7) is intended to supply power to primarily intended as the centralized power

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SECTION 501- 136-100

4:1:::_'?:::J:_I!J::N_i _Ji_i_:

Fig. 5--2012B Transformer

Fig. 6--2012C Transformer power 30 dial light telephone sets.

....... .......

Fig. 7--2012D Transformer

instances where frequent customer
contact may result in short circuits

that will affect service, the
transformer may be mounted in

a 105C (plastic) apparatus box.

4. KS-16940L1 VOLTAGE REGULATING (V.R.)
TRANSFORMER

4.01 KS-16940L1 V.R. transformer (Fig. 9) is

primarily for use as centralized dial light

power source to provide regulated power for dial
lights and night lights on telephones. It will

supply for multiphone dial light installations and power cord and plug. The ground prong

4.02 Input is provided with a 2-foot 3-conductor

home interphone systems requiring approximately of the plug is connected internally to the transformer
6 volts. It is capable of handling up to ten dial case. The output is isolated from the input and

light stations. Additional taps at 10.5, 24.0, and the case and is terminated in two low voltage

25.5 volts are also provided for other possible uses. terminals on the case.
This transformer is self-protecting with an automatic

reset thermo switch. 4.03 Output taps of 6.3 and 8.0 volts are located

onback of cover as shown in Fig. 10. The

3.02 Overall dimensions of the transformer are transformer is shipped with movable lead connected
2-3/4 by 3-3/4 by 2-3/4 inches. Power cord to 6.3-volt tap.

is 18 inches long and terminates in a 2-pronged
plug. Weight is approximately 1-1/2 pounds. 4.04 The 8-volt tap should be used to provide

illumination for PRINCESS telephone sets.

3.03 Keyhole slots provide easy installation. Use
a suitable backboard when mounting on 4.05 To change connection to 8.0-volt tap.

surfaces requiring backboards.

(1) Remove plug from power outlet, if connected.

not hazardous and short circuits across (2) Remove two screws holding cover to case.

these terminals will not damage the
The exposed low-voltage terminals are

KS-16886L2 transformer. However in (3) Remove cover.

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