ANSI @

C57.12.26-1987
Revision of
ANSI C57.12.26-1975

American National Standard

for Transformers -
Pad-Mounted Compartmental-Type,
Self-Cooled, Three-phase Distribution Transformers
for Use with Separable Insulated High-Voltage
Connectors, High-Voltage, 34 500 Grd Y/19 920 Volts
and Below; 2500 kVA and Smaller

Secretariat
Institute of Electrical and Electronics Engineers
National Electrical Manufacturers Association

,Approved April 16, 1986

,American National Standards Insitute, I nc

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 Approval of an American National Standard requires verification by ANSI that the re-
erican quirements for due process. consensus. and other criteria for approval have been met by
ational the standards developer.
Consensus is established when, in the judgment of the ANSI Board of Standards Review,
substantial agreement has been reached by directly and materially affected interests. Sub-
stantial agreement means much more than a simple majority, but not necessarily unanim-
ity. Consensus requires that all views and objections be considered, and that a concerted
effort be made toward their resolution.
The use of American National Standards is completely voluntary; their existence does not
in any respect preclude anyone, whether he has approved the standards or not, from man-
ufacturing, marketing. purchasing. or using products, processes, or procedures not con-
forming t o the standards.
The American National Standards Institute does not develop standards and will in no cir-
cumstances give an interpretation of any American National Standard. Moreover, no per-
son shall have the right or authority to issue an interpretation of an American National
Standard in the name of the American National Standards Institute. Requests for inter-
pretations should be addressed to the secretariat or sponsor whose name appears on the
title page of this standard.
CAUTION NOTICE: This American National Standard may be revised or withdrawn at
any time. The procedures of the American National Standards Institute require that
action be taken t o reaffirm, revise, or withdraw this standard no later than five years from
the date of approval. Purchasers of American National Standards may receive current infor-
mation on all standards by calling or writing the American National Standards Institute.

Published by

American National Standards Institute

1430 Broadway, New York, New York 10018

Copyright 0 1987 by American National Standards Institute, Inc

A11 rights reserved.

No part of this publication may be reproduced in any form,

in an electronic retrieval system or otherwise, without
the prior written permission of the publisher.

Printed in the United States of America

A I M287/10

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
Foreword (This Foreword is not part of American National Standard (257.12.26-1987.)
The Accredited Standards Committee on Transformers, Regulators, and Reactors, C57,
has for a number of years been developing and correlating standards on transformers and
regulators. The data used in this work have been gathered from many sources, including
the standards of the Institute of Electrical and Electronics Engineers and the National
Electrical Manufacturers Association, reports of committees of the Edison Electric Insti-
tute, and others.
This standard and the related standards on three- and single-phase distribution trans-
formers were prepared by the Subcommittee on Distribution Transformers, Overhead
and Pad-Mounted, (37.12.2.
Suggestions for improvement of this standard will be welcome. They should be sent to
the National Electrical Manufacturers Association, 2101 L Street, NW, Washington, DC
20037.
This standard was processed and approved for submittal to ANSI by Accredited Standards
Committee on Transformers, Regulators, and Reactors, C57. Committee approval of the
standard does not necessarily imply that all committee members voted for its approval.
At the time it approved this standard, the C57 Committee had the following members:

R. L. Ensign, Chair
C. H. White, Secretary

Organization Represented Name of Representative

Electric Light and Power Group. .......................... W. Cole
G. Gunnels
I. Koponen
P. Orehek
D. Soffrin (Alt)
A. Velazquez
Institute of Electrical and Electronics Engineers . . . . . . . . . . . . . . . . . R. Ensign
F. Huber (Alt)
L. McCormick
W. Neiswander
H. Smith (Alt)
B. Stanleigh (Alt)
H. Tucker
National Electrical Manufacturers Association . . . . . . . . . . . . . . . . . . R. Brown (Alt)
P. Cacalloro (Alt)
P. Dewever (Alt)
J. Douglass
W. Kendall
K. Linsley
G. Maya11 (Alt)
W. McNutt
J. Nay (Alt)
T. Reback ( A t )
D. Strang (At)
R. Uptegraff, Jr
Tennessee Valley Authority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Smith
Underwriters Laboratories, Inc . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Seelbach
W. O’Grady (Alt)
U.S.Department of Agriculture,
Rural Electrification Administration . . . . . . . . . . . . . . . . . . . . . . . J. Arnold, Jr
U.S. Department of Energy,
Western Area Power Administration . . . . . . . . . . . . . . . . . . . . . . . D. Torgerson
U.S.Department of the Interior, Bureau of Reclamation . . . . . . . . . . . . F. Cook, SI
U.S. Department of the Navy,
Naval Facilities Engineering Command. . . . . . . . . . . . . . . . . . . . . . H. Stickley

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 Subcommittee C57.12.2 on Distribution Transformers, Overhead and Pad-Mounted,
which was responsible for developing this standard, had the following members:

R. L. Ensign, Chair J. C. Amold, JI M. E. Kemph

H. W. Book R. J. Manes
R. G. Hansen, Secretary D. R. Brown G. W. Mayall
D. C. Burrett R. P. Miller
W. E. Cole N. M. Neagle
C. C. Dixon J. R. Newton
R. Garanich D. W. Rose
M. Gruber J. C. Thompson
G . D.Hovey W. E. Whitely
J. Hunt A. L. Wilks
C. A. Kappeler L. Williams

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
Contents SECTION PAGE

1. ScopeandPurpose ........................................... 7
2 . Related Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Revision of American National Standards. . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Kilovolt-Ampere Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Voltage Ratings and Tap Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 . Basic Lightning Impulse Insulation Levels and Dielectric Test Levels . . . . . . . . . . . 8
5 . Impedance Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1 Percent Impedance Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2 Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3 Tolerance on a Tap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2 DielectricTest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.3 Reference Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7 . Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2 Connectors and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.3 High-Voltage and Low-Voltage Compartments . . . . . . . . . . . . . . . . . . . . . . 11
7.4 Instruction Nameplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.5 Oil Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.6 Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.7 Components for Loop Primary Cable Systems . . . . . . . . . . . . . . . . . . . . . . . 12
8 . Other Requirements That May Be Specified for Some Applications . . . . . . . . . . . . 12
Tables
Table 1 Range of kVA and Voltage Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 2 High-Voltage Taps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 3 Electrical Characteristics of Low-Voltage Terminals and
Minimum Electrical Clearances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 4 Transformers and Connectors High-Voltage Ratings
and Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figures
Figure 1 Minimum Dimensions for Radial-Feed Transformers . . . . . . . . . . . . . 1 3
Figure 2 Minimum Dimensions for Loop-Feed Transformers . . . . . . . . . . . . . . 14
Figure 3 Compartment Designations and Minimum Dimensions
for Loop-Feed or Radial-Feed Transformers. . . . . . . . . . . . . . . . . . . 15
Figure 4 Low-Voltage Terminal Arrangements and Minimum Dimensions. . . . . . 16
Figure 5A Specific Dimensions for Radial-Feed Transformers . . . . . . . . . . . . . . . 17
Figure 5B Specific Dimensions for Radial-Feed Transformers . . . . . . . . . . . . . . . 18
Figure 6A Specific Dimensions for Loop-Feed Transformers . . . . . . . . . . . . . . . 19
Figure 6B Specific Dimensions for Loop-Feed Transformers . . . . . . . . . . . . . . . 20
Figure 6C Specific Dimensions for Loop-Feed Transformers . . . . . . . . . . . . . . . 21
Figure 7 Compartment Designations and Specific Dimensions for
Loop-Feed and Radial-Feed Transformers . . . . . . . . . . . . . . . . . . . . 22
Figure 8 Low-Voltage Terminal Arrangements and Specific Dimensions . . . . . . . 2 3
Figure 9 Low-Voltage Terminals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 10 Angular Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 11 Captive and Recessed Pentahead and Hex Head Bolts . . . . . . . . . . . . . 27

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 American National Standard
for Transformers -

Pad-Mounted Compartmental -Type,

Self -Cooled, Three-phase Distribution Transformers
for Use with Separable Insulated High-Voltage
Connectors, High-Voltage, 34 500 Grd Y/19 920 Volts
and Below; 2500 kVA and Smaller

1. Scope and Purpose wise specified herein, shall be in accordance with the
following American National Standards (see 2.2):
1.1 This standard is intended for use as a basis for de-
ANSI (257.12.20-1981, Requirements for Overhead-
termining performance, interchangeability, and safety
Type Distribution Transformers, 500 kVA and Smaller:
of the equipment covered, and to assist in the proper High-Voltage, 67 000 Volts and Below, Low-Voltage,
selection of such equipment. 15 000 Volts and Below
1.2 This standard covers certain electrical, dimensional, ANSI C57.12.70.1978, Terminal Markings and Connec-
and mechanical characteristics and takes into considera- tions for Distribution and Power Transformers
tion certain safety features of three-phase, 60-Hz, min-
eral-oil-immersed, self-cooled, pad-mounted, compart- ANSI/IEEE C57.12.00-1980, General Requirements
mental-type distribution transformers with separable for Liquid-Immersed Distribution, Power, and Regulat-
insulated high-voltage connectors. These transformers ing Transformers
are rated 2500 kVA and smaller, with high voltages of
ANSI/IEEE (37.12.80-1978, Terminology for Power
34 500 Grd Y/19 920 volts and below, and with low
and Distribution Transformers
voltages of 480 volts and below. These transformers are
glenerally used for step-down purposes from an under- ANSI/IEEE (37.12.90-1980, Test Code for Liquid-
ground primary cable supply. Immersed Distribution, Power, and Regulating Trans-
NOTE: Refer to latest Federal Regulations concerning poly- formers and Guide for Short-circuit Testing of Distri-
chlorinated biphenyl (PCB) contamination in transformers. bution and Power Transformers
1.3 This standard covers connector and terminal ar- ANSI/IEEE (37.91-1981, Guide for Loading Mineral-
rangements for both radial-feed and loop-feed systems. Oil-Immersed Overhead and Pad-Mounted Distribution
Either certain minimum dimensions (see Figures 1 Transformers Rated 500 kVA and Less with 65°C or
through 4) or certain specific dimensions (see Figures 5 55°C Average Winding Rise
through 8) shall be specified.
ANSI/IEEE C57.92-1981, Guide for Loading Mineral-
1.4 This standard does not cover the electrical and Oil-Immersed Power Transformers up to and including
mechanical requirements of any accessory devices that 100 MVA with 55°C or 65'C Winding Rise
may be supplied with the transformer.
ANSI/IEEE 386-1985, Separable Insulated Connector
Systems for Power Distribution Systems above 600V
2.2 Revision of American National Standards.When
2. Related Standards an American National Standard referred to in this doc-
ument is superseded by a revision approved by the
21.1 General. All characteristics, definitions, terminol- American National Standards Institute, Inc, the revi-
ogy, voltage designations, and tests, except as other- sion shall apply.

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD (37.12.26-1987

Table 1
Range of kVA and Voltage Ratings
3.1 Kilovolt-Ampere Ratings. Kilovolt-ampere ratings kV A Ratings
are continuous and based on not exceeding either a
Low-Voltage Low-Voltage
65°C average winding temperature rise or an 80°C hot- High-Voltage Rdtings Ratings (volts) Ratings (volts)
spot conductor temperature rise. The temperature rise (volts) 208Y/120, 240 480Y/277,480
of the insulating oil shall not exceed 65°C when mea- Delta or wye
sured near the top of the tank. These kilovolt-ampere 2 400 75- 750 75- 750
ratings are based on the temperature and service condi- 4 160 75-1000 75-1000
4 800 75-1000 75-1500
tions specified in ANSI/IEEE C57.12.00-1980. The 7 200 75-1000 75-2000
kilvolt-ampere ratings shall be as follows: 12 000,12 470 75-1 000 75-2500
13 200, 13 800, 16 340 75-1000 75-2500
75 500 Grounded wye
112-1/2 750 22 860,23 900,24 940 75-1000 75-2500
1so 1000 34 500 75-1000 75-2500
225 1.500
NOTES :
300 2000 (1) Kilovolt-ampere ratings separated by a dash indicate that
2500 all intervening ratings covered in this standard are included.
(2) Unsymmetrical loading of wye-wye connected units may
3.2 Voltage Ratings and Tap Ratings cause heating of their tanks in excess of that which would be
3.2.1 Voltage ratings shall be in accordance with produced by balanced conditions. To reduce the probability of
tank heating, such units shall be provided with a core construc-
Table 1. tion that will not saturate when 33% zero sequence voltage is
3.2.2 Voltage taps shall be as given in Table 2. The applied.
tap changer handle in the terminating compartment (3) For complete connector ratings, see ANSI/IEEE 386-
1985.
shall be marked for de-energized operation.

than the total tap voltage range and shall be expressed

as a percentage of the rated voltage.
4. Basic Lightning Impulse Insulation Levels
and Dielectric Test Levels
6. Tests
4.1 Basic lightning impulse insulation levels (BILs)
shall be in accordance with Tables 2 and 3. 6.1 General. Except as specified in 6.2, tests shall be
4.2 Dielectric test levels shall be in accordance with performed as specified in ANSI/IEEE C57.12.00-1980
the distribution levels specified in Table 4 of ANSI/ and ANSI/IEEE (257.12.90-1980.
IEEE (257.1 2.00-1980. 6.2 Dielectric Test. For wye-wye connected units, the
transformer primary is designed for solidly grounded
application, and no applied-potential test is required.
The induced-potential test shall be performed by ap-
5 . Impedance Voltage plying, between the terminals of each winding, a volt-
age that will develop from the high-voltage line ter-
5.1 Percent Impedance Voltage. The percent imped-
minals to ground a voltage of 1000 volts plus 3.46
ance voltage, as measured on the rated voltage connec-
times rated transformer winding voltage, but in no
tion, shall be as follows:
case shall the line-to-ground voltage developed exceed
kVA Rating Percent Impedance Voltage 40 000 volts for 125 kV BIL and 50 000 volts for 150
kV BIL. For this test the neutral terminal shall be
75-500 Not Specified
grounded. However, under conditions where the neu-
750-2500 5.75
tral terminal ground connection can be removed, both
5.2 Tolerance. The tolerance on impedance voltage the applied potential test and the induced potential
shall be as specified in 9.2 of ANSI/IEEE C57.12.00- test as specified in ANSI/IEEE C57.12.00-1980 may
1980. be performed.
5.3 Tolerance on a Tap. The percent departure of the 6.3 Reference Temperature. The reference tempera-
tested impedance voltage on any tap from the tested ture to which losses, impedance, regulation, and effi-
impedance voltage at rated voltage shall not be greater ciency are corrected shall be 85°C.

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

Table 2
High-Voltage Taps
High-Voltage Tam
75- 5 00 kVA
Low- LOW-
Voltaee Voltaee
Ratinis Ratings 340,
High- 208Y/120 48OY/277,480 750-2500 kVA
Voltage (volts) (volts) Low-Voltage Ratings
Ratings BIL 208Y/120,240
(volts) (kV) Below Above Below 48OY/277,480 (volts)
2 400 45 4-2-1 12% 2-2-1 12% 2-2-112% 2520/2460/2340/2280
4 160 60 4-2-1 12% 2-2-112% 2-2-1 12% 4360/4260/4055/3950
4 800 60 4-2-1 12% 2-2-112% 2-2-1 12% 5040/4920/4680/4560
7 200 75 4-2-1 12% 2-2412% 2-2-1 12% 756017380/7020/6 840
12 000 95 4-2-112% 2-2412% 2-2-112% 12 600112 30011 1 70011 1 400
12 470 95 4-2-1 12% 2-2-1 12% 2-2-1 12% 13 090112 780112 160111 850
13 200 95 4-2-112% 2-2-112% 2-2-1 12% 13 860113 530112 870112 540
13 800 95 4-2-112% * * 14 400114 100113 500113 200
16 340 95 * * * 17 200116 770115 910115 480
:22 860 Grd Y113 200 125 4-2-112% 2-2-1 12% 2-2-1 12% 24 003123 431122 288121 717
23 900 Grd Y/13 800 125 4-2-112% 2-2-112% 2-2-112% 25 095124 497123 302122 705
24 940 Grd Y/14 400 125 4-2-112% 2-2-1 12% 2-2-1 12% 26 187125 563124 316123 693
134 500 Grd Y/19 920 150 4-2-112% 2-2-1 12% 2-2-112% 36 225135 363133 638132 775

*Taps are the same as those for 750-2500 kVA ratings (see last column).

Table 3
Electrical Characteristics of
Low-Voltage Terminals and Minimum Electrical Clearances
60-HZ Minimum Minimum
Dry One- Clearance, Clearance,
Low-Voltage Minute Live Parts Live Parts
Ratings BIL Withstand to Ground* Phase to Phase*
(volts) (kv) (kV) (inches) (inches)
208Y/120 30 10 1 1
240 30 10 1 1
48OY1277 30 10 1 1
4 80 30 10 1 1

*These dimensions should be increased wherever possible to allow for

ease in making connections by the user.

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

Table 4
Transformers and Connectors
High-Voltage Ratings and Electrical Characteristics
Electrical Characteristics of
Transformer Completely Assembled High-Voltage Connectors*
High-Voltage Ratings
High-Voltage 60-Hz Dry One-
Ratings BIL Phase to Ground Phase to GroundIPhase to Phase BIL Minute Withstand
(volts) (kV) (kV) (kV) (kV) OtV)
2400 45 8.3 8.3114.4 95 34
4160 to 4800 60 8.3 8.3/14.4 95 34
7200 15 8.3 8.3114.4 95 34
12 000 to 16 340 95 8.3 or 8.3114.4 or 95 or 34 or
15.2t 15.2126.37 125t 40t
22 860 Grd Y to 125 15.2 15.2126.3 125 40
24 940 Grd Y
34 500 Grd Y 150 21.1 21.1136.6 150 50

*For complete connector ratings, see ANSIIIEEE 386-1985.

?Required connector rating should be specified.

7. Construction fore the high-voltage door can be opened. Where the

low-voltage compartment door is of a flat panel design,
7.1 General. A pad-mounted compartmental-type the compartment door shall have three-point latching
transformer shall consist of a tank with high-voltage with a handle provided for a locking device. Hinge
and low-voltage cable terminating compartments as pins and associated barrels shall be corrosion-resistant
shown in Figure 3 or Figure 7. The compartments material, passivated AIS1 Type 304 or the equivalent.
shall be separated by a barrier of metal or other rigid 7.1.4 The transformer tank and compartments shall
material, be so constructed as to limit disassembly, breakage,
The transformer tank and compartments shall be as- and prying open of any doors, panels, and sills with
sembled as an integral unit suitable for flush mounting the doors in the closed and locked position.
on a flat rigid surface. The assembly shall restrict the 7.1.5 There shall be no exposed screws, bolts, hing-
elltry of water (other than flood water) into compart- ing, or fastening devices that are externally removable.
ments so as not to impair the operation of the trans- In addition, there shall be no openings through which
former. foreign objects such as sticks, rods, or wires might be
7.1.1 Cabinet security as described in 7.1.2 through inserted to contact live parts.
7.1.1 1 shall be evaluated in accordance with the test 7.1.6 The door handle and hasp shall be designed
procedures and requirements of the design test method and constructed of a material to limit breaking or
for cabinet security described in the NEMA Standards bending. The door handle and the provision for locking
Publication for Transformers, Regulators, and Reactors, device on the low-voltage compartment door shall be
NEMA TR 1-1980.' designed and located to limit prying, cutting, or break-
7.1.2 The high-voltage and low-voltage compart- ing of the locking mechanism.
ments shall be located side-by-side on one side of the 7.1.7 One or more captive and recessed pentahead
transformer tank. When viewed from the front, the or hex-head bolts shall be provided for additional secur-
low-voltage compartment shall be on the right. ity of the low-voltage compartment door. A blind bolt
7.1.3 Each compartment shall have a door so con- hole shall be provided. The design of the captive and
structed as to provide access to the high-voltage com- recessed bolt shall be in accordance with Figure 11.
partment only after the door to the low-voltage com- Bolts shall be constructed of a corrosion-resistant mate-
partment has been opened. There shall be one or more rial, and the design shall minimize the possibility of
additional fastening devices that must be removed be- misalignment and cross threading.
7.1.8 Transformers with handholes shall have a
l Available from the National Electrical Manufacturers Asso-
cover that is removable only after being unfastened
ciation, 2101 L Street, NW, Washington, DC 20037. from inside the compartments.

10

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD (257.12.26-1987

7.1.9 The bottom edges of the compartments shall 7.2.5 Low-voltage line and neutral terminals shall
be so constructed as to provide for the use of hold- be in accordance with Figure 4(a), 4(b), 8(a), or 8(b)
down devices that are accessible only from inside the and arranged for vertical takeoff. Terminal dimensions
compartments. shall be as shown in Figure 9(a), 9(b), 9(c), or 9(d), as
7.1.10 Construction of the unit shall be such that it specified.
can be lifted, skidded, or slid, or any combination of 7.2.6 The low-voltage neutral shall be either a blade
these, into place on the mounting surface without dis- connected directly to the tank or a fully insulated ter-
turbing the high-voltage or low-voltage cables. minal. If a fully insulated terminal is used, a ground
7.1.11 All compartments and transformer surfaces pad shall be provided on the outer surface of the tank.
in contact with the mounting surface and a minimum One or more removable ground straps suitably sized
of 1 inch above the mounting surface shall be designed for the short-circuit rating of the transformer, as de-
or treated to minimize corrosion. The underside of the fined in ANSI/IEEE C57.12.00-1980, shall be provided
tank, when within 1 inch of the mounting surface, shall and connected between the low-voltage neutral termi-
also be designed or treated to minimize corrosion. nal and the ground pad.
7.1.12 Jack bosses or jacking facilities shall be pro- 7.2.7 For wye-wye connected units, the high-volt-
vided on the tank. The vertical clearance for a jack age neutral shall be connected to the low-voltage neu-
shall be 1-112 inches minimum, 6-1/2 inches maximum. tral internally, with provision for opening this connec-
7.1.13 The transformer shall be arranged for rolling tion for testing.
in two directions: parallel to and at right angles to one 7.2.8 Connector and terminal designations shall be
side of the transformer. as defined in ANSI C57.12.70-1978. The high-voltage
7.1.14 The transformer shall be provided with lift- connector and low-voltage terminal designations and
ing provisions that are permanently attached and ar- locations shall be as shown in Figures 1 through 4 or 5
ranged on the tank to provide a distributed balanced through 8.
lift in a vertical direction for the completely assembled The identification of connector and terminal con-
transformer and shall be designed to provide a safety nections shall be as shown on the instruction name-
factor of 5 . The safety factor of 5 is the ratio of the plate.
ultimate stress of the material used to the working stress. 7.2.9 The angular displacement shall be as shown in
The working stress is the maximum combined stress Figure 10.
developed in the lifting provisions by the static load on
the completely assembled transformer. 7.3 High-Voltage and Low-Voltage Compartments.
The compartment doors shall be of sufficient size to
7.2 Connectors and Terminals provide adequate operating and working space when
7.2.1 The electrical characteristics of the com- removed or open. The doors shall either be equipped
pletely assembled high-voltage connectors shall be as for latching in the open position or designed for man-
shown in Table 4. The electrical characteristics and ual removal.
clearances of the completely assembled low-voltage
terminals shall be as shown in Table 3. 7.4 Instruction Nameplate
7.2.2 The number, location, and arrangement of 7.4.1 The instruction nameplate shall be located in
the high-voltage connectors and low-voltage terminals the low-voltage compartment and shall be readable
shall be as shown in Figures 1 through 4 or 5 through 8. with the cables in place. Where the nameplate is
7.2.3 High-voltage connectors shall be provided for mounted on a removable part, the manufacturer's
connection to the distribution system through separable name and transformer serial number shall be perma-
insulated high-voltage connectors. The high-voltage nently affixed to a nonremovable part.
connectors shall consist of either bushing wells, bush- 7.4.2 The nameplate shall conform to ANSI/IEEE
ing wells with bushing inserts, or integral bushings, as C57.12.00-1980: nameplate A for 500 kVA and below;
specified. Cable accessory parking stands shall be pro- nameplate B for 750 kVA and above. The high-voltage
vided. For specific details concerning high-voltage BIL shall be included on the nameplate.
separable connectors and cable accessory parking
stands, refer t o ANSI/IEEE 386-1985. Separable insu- 7.5 Oil Preservation
lated high-voltage connectors that are designed for 7.5.1 Transformers shall be of sealed-tank construc-
operation after the transformer is in place shall be tion. Sealed-tank construction is that construction
located so that they can be operated with hot-line tools. which seals the interior of the tank from the atmo-
7.2.4 When provided, the high-voltage neutral bush- sphere and in which the gas volume plus the oil volume
ing may be two insulation classes below that for the remains constant. The transformer shall remain effec-
phase bushings. tively sealed for a top-oil temperature range of - 5 O C to

11

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

+105'C, continuous, and under the operating condi- 7.6.2 Unless otherwise required, welded main-cover
tions described in ANSI/IEEE C57.91-1981 and ANSI/ construction shall be provided. Where access t o internal
IEEE C57.92-1981. connections for test purposes or internal tap changer is
7.5.2 A replaceable valve to relieve excess pressures required, one or more handholes shall be provided.
shall be furnished in the low-voltage compartment on 7.6.3 Where a bolted-on cover of any kind is used,
the tank wall above the 140°C top oil level, by manu- the construction shall conform t o 7.1.
facturer's calculation, and shall be located so as not 7.6.4 The tank ground provision shall consist of the
to interfere with the use o f the low-voltage terminals or following pads:
the operating handle of the low-voltage circuit breaker. (1) 500 kVA and below. two steel pads, each with
The inlet port shall be 1/4 inch or larger NPT (or a 1/2-13 UNC tapped hole, 7/16 inch deep.
N F thread with gasket), sized for a specified minimum (2) Above 500 kVA: two unpainted, copper-faced
flow rate. steel or stainless steel pads, 2 X 3-1/2 inches each, with
Exposed parts shall be of weather- and corrosion- two holes spaced on 1-3/4-inch centers and tapped for
resistant materials. 1/2-13 UNC thread. The minimum thickness of the
Gaskets and O-rings shall withstand oil vapor and copper facing shall be 0.015 inch. The minimum thread
105°C temperature, continuous, under the operating depth of holes shall be 1/2 inch.
conditions described in ANSI/IEEE C57.9 1-1981 and
These ground pads shall be welded on or near the trans-
ANSI/IEEE C57.92-1981 without seizing or deteriorat-
former base. one in the high-voltage compartment and
ing for the life of the transformer.
one in the low-voltage Compartment. In cases where
The valve shall have a pull ring for manually reduc-
the transformer tank and compartments are separate,
ing pressure to atmospheric, using a standard hook-
provisions shall be made for electrically connecting
stick, and be capable of withstanding a static pull force
them.
of 25 pounds for 1 minute without permanent defor-
mation. The valve shall withstand a static force of 7.7 Components for Loop Primary Cable Systems. The
100 pounds for 1 minute applied normal t o its longi- minimum current-carrying capabilities of components
tudinal axis at the outmost extremity of the body. for looped primary systems shall be 200 amperes (con-
When specified, the venting port o n the outward tinous current rating) and 1 0 000 amperes rms sym-
side of the valve head seat shall be protected t o prevent metrical for 0.17 second (short-time current rating) for
entry of dust, moisture, and insects before and after transformers with or without high-voltage switching.
the valve has been actuated; or a weather-cap-type indi-
cator shall be provided that will remain attached t o
the valve and provide positive indication to an observer
8. Other Requirements That May Be Specified
that the valve has operated. Venting and sealing charac-
for Some Applications
teristics shall be as'follows:
Cracking pressure: 1 0 psig k 2 psig 8.1 Certain specific applications call for transformer
Resealing pressure: 6 psig minimum requirements not covered in Sections 3 through 7;
Leakage from resealing pressure t o minus 8 psig: 0 Section 8 comprises descriptions o f the most frequently
Flow at 15 psig: 35 SCFM minimum" used requirements for such transformers. They shall be
met only when specified in conjunction with the re-
*SCFM is flow in cubic feet per minute, corrected
quirements of Sections 3 through 7. These specific re-
for air pressure o f 14.7 psi and air temperature of
quirements may change the dimensions in Figures 5
2 1.1"c.
through 8.
7.6 Tanks 8.2 When specified, high-voltage windings without
7.6.1 The tank shall be of sufficient strength t o taps shall be provided. In addition, when specified, taps
withstand a pressure of 7 psig without permanent dis- other than those covered in Table 2 shall be provided.
tortion and 12 psig without rupturing or displacing
8.3 When specified, additional high-voltage and low-
other compoents of the transformer or affecting cabi-
voltage accessories shall be provided. Accessories that
net security as described in 7.1 .I. A 1-inch upper plug
are suitable only for de-energized operation shall be so
(or cap) for filling and pressure testing shall be pro-
marked.
vided. A 1-inch NPT drain plug (or cap) for transfor-
mers rated 75 -500 kVA and a 1-inch NPT drain valve 8.4 When specified, low-voltage terminal construction
with built-in sampling device for transformers rated shall be adequate for the application of a user-defined
750-2500 kVA shall be provided. current transformer.

12

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

8.5 When specified, the lifting provisions covered in 8.8 When specified for wye-wye connected units, the
7.1.14 shall be removable from the tank. high-voltage neutral shall be solidly connected internally
to the transformer tank wall, or the high-voltage neu-
8.6 When specified, a high-voltage rating of 34 500
tral shall be brought out through a separate bushing
lCrd'/I9 920 with 125 kV BIL be provided. into the high-voltage
~. portion of the compartment and
8.7 When specified for wye-wye connected trans- grounded externally.
formers, the core construction shall be of the triplex
(single-phase cores) construction.

P
(NOTE 4)
A
I
I I
* H L K - K A K & - I - & K 4 H -
D
ID I M ENSI ON
ClN FIGURE 3

L BASE
PLANE

Separable Insulated Connectors with High-Voltage Ratings of

8.3 and 8.3114.4 kV 15.2 and 15.2/26.3 kV 21.1 and 21.1/36.6 kV
kVA
Ratings H K P H K P H K P
75-150 2.3 4.0 4.5 2.9 4.0 4.5 4.0 6 .O 7.5
225-500 3.0 4.0 4.5 3.0 4.0 4.5 4.0 6 .O 7.5
750-2500 3.2 4.0 4.5 3.2 4.0 4.5 4.0 6 .O 7.5

NOTES:
(1) High-voltage connector arrangements and dimensions are for applications requiring certain minimum dimensions.
(2) All dimensions are in inches and are minimum.
(3) The above minimum dimensions do not provide for all types of parking-stand-mounted devices.
(4) For bail clearances, when specified, P = 11 inches for 8.3/14.4-KV connectors, 14.0 inches for 15.2-kV and
15.2126.3-kV connectors, and 17.0 inches for 21.1-kV and 21.1/36.6-kV connectors.
(5) Configuration for 21.1/36.6kV connectors is based on ANSI/IEEE 386-1985, Figure 7, designation interface for
separable insulated connectors.

Figure 1
Minimum Dimensions for Radial-Feed Transformers

13

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

Q LOWEST
H IG H-VOLTAG E

t P

3 4’

BASE
PLANE

Separable Insulated Connectors with High-Voltage Ratings of

8.3 and 8.3114.4 kV 15.2 and 15.2126.3 kV 21.1 and 21.1136.6 kV
kVA
Ratings H N M K P H N M K P H N M K P
All 3.0 4.0 3.0 4.0 4.5 3.0 4.0 3.5 4.5 4.5 4.0 4.0 3.75 6.0 7.5

NOTES:
(1) High-voltage connector arrangements and dimensions are for-applications requiring certain specific dimensions.
(2) All dimensions are in inches and are minimum.
(3) The above minimum dimensions do not provide for all types of parking-stand-mounted devices.
(4) For bail clearances, when specified, P = 11 inches for 8.3/14.4-kV connectors, 14.0 inches for 15.2-kV and
15 2/26.3kV connectors, and 17.0 inches for 2 1 . l k V and 21.1/36.6kV connectors.
(5) Configurations are based on ANSIIIEEE 386-1985, Figure 7 , designation interface for separable insulated connectors.

Figure 2
Minimum Dimensions €or Loop-Feed Transformers

14

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

H IGH-VOLTAGE
COMPARTMENT
I
I LOW-VOLTAGE
7
BOTTOM -----C 1c

FLANGE
314 M I N
I
1-1/2 MAX
3 MAX RIGID BARRIER

VOLTAGE

---/----
COMPARTMENT
AND
- - - - ----- HIGH-VOLTAGE

Q LOWEST HIGH-
VOLTAGE PHASE
CONNECTOR
I
I
1
I
I
Q LOWEST LOW-
VOLTAGE
TERMINAL
7 E
COMPA RTM ENT

1 .
I
MAX
3 { BASE
PLAN E

Separable Insulated Connectors

with High-Voltage Ratings of
8.3 or 15.2 kV 21.1 kV
LVA Low-Vol tage
Ratings Ratings (volts) D E F D E F
75-500 All 21 20 18 21 20 21
750-1000 240,208Y/120 27 27 18 27 27 21
750-2500 480,480YI277 27 27 18 27 27 21

NOTES:
(1) High-voltage connector arrangements and dimensions are for applications requiring
certain minimum dimensions.
(2) All dimensions are in inches and are minimum unless otherwise specified.

Figure 3
Compartment Designations and Minimum Dimensions
for Loop-Feed or Radial-Feed Transformers

15

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C5 7.12.26-1987

LVA Ratings A B
75-150 3 6
225-500 4 8
750-2500 5 8

(a) Staggered Low- Voltage Terminal Arrangement

t
4
( b ) In-Line Low- Voltage Terminal Arrangement

NOTES
(1) Low-voltage terminal arrangements and dimensions are for applications requiring certain minimum
dimensions.
(2) All dimensions are in inches and are minimum.
(3) This is the dimension to the rigid barrier between the high-voltage compartment and the low-voltage
compartment.

Figure 4
Low-Voltage Terminal Arrangements
and Minimum Dimensions

16

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C5 7.12.26-1987

r Q HIGH-VOLTAGE CONNECTORS

D
DIME NSlON
ON FIGURE 7

BASE

TANK SURFACE

0.75
+ 118
-0
INSIDE
Cable Accessory Parking Stand

Separable Insulated Connectors with High-Voltage Ratings of

8.3 and 8.3114.4 kV 15.2 and 15.2126.3 kV 21.1 and 21.1136.6 kV
kVA
Ratings H K P H K P H K P
All 3.5 5.0or6.5 4.5 4.5 6.5 4.5 5 .O 7 .O 7.5

NOTES:
(1) High-voltage connector arrangements and dimensions are for applications r e q u h g certain specific dimensions.
(2) Configuration of 2 1 . l k V and 21.1/36.6kV connectors is based on ANSI/IEEE 386-1985, Figure 7 , designation
interface for separable insulated connectors.
(3) All dimensions are in inches.
(4) H and P are minimum dimensions. Dimension K has a tolerance of *0.25 inch.
(5) For bail clearance, when specified, P = 11 inches for 8.3/14.4-kV connectors, 14.0 inches for 15.2-kV and
15.2/26.3-kV connectors, and 17.0 inches for 21.1-kV and 21.1/36.6kV connectors.

Figure SA
Specific Dimensions for Radial-Feed Transformers

17

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD (37.12.26-1987

Q HIGH-VOLTAGE CONNECTORS

/ -7-
P = 7.5

-!!.YE 5’

D
I
DIMENSION
ON FIGURE 7

TANK SURFACE

Separable Insulated Connector

High-Voltage Ratings of
21.1 and 21.1/36.6 kV
kVA
Ratings H K -0
All 5 .o 5 .O INSIDE

NOTES:
(1) High-voltage connector arrangements and dimensions are for applications requiring certin specific dimensions.
(2) Configuration is based on ANSI/IEEE 386-1985, Figure 8, designation interface.
(3) All dimensions are in inches,
(4) H and P are minimum dimensions. Dimension K has a tolerance of k0.25 inch.
(5) For bail clearance, when specified, P = 20 inches for 21.lkV and 21.1/36.6kV connectors.

Figure 5B
Specific Dimensions for Radial-Feed Transformers

18

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C5 7.12.26-1987

-K
I BELOW Q

P = 4.5
(NOTE 4)
1
N
t B Q O F LOWEST
I H IGH-VOLTAGE
N I CONN ECTOR
t
D DIMENSION
ON FIGURE 7
I I I I I BASE
1
PLAN E
- M-c* M--- K- K- M 7

CL I-K-4

--rl MIN
TANK
/////p/,//// 0.75
su R FACE 7 I + 118

Cable Accessory
Parking Stand

Separable Insulated Connectors with High-Voltage Ratings of

8.3 and 8.3114.4 kV 15.2 and 15.2126.3 kV
kVA
Ratings H N M K H N M K
All 3.5 6.0 4.5 5.0 or 6.5 4.5 6.0 4.5 6.5

NOTES:
(1) High-voltage connector arrangements and dimensions are for applications requiring certain specific di-
mensions.
(2) All dimensions are in inches.
(3) H and P are minimum dimensions. Dimension K, M, and N have a tolerance of i0.25 inch.
(4) For bail clearance, when specified, P = 11 inches for 8.3/14.4-kV connectors and 14.0 inches for
15.2-kV and 15.2126.3-kV connectors.

Figure 6A
Specific Dimensions for Loop-Feed Transformers

19

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

W
-m z
4
a

r
irY-
c
Y

tc
E

fL
I

20

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

-f--
I

tY
r

t
U"
f

L
U"
t
2
F-
i

21

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

BOTTOM
H IGH-VOLTAG E
f F MIN INSIDE
FLANGE --s-
314 MIN
1-1/2 MAX
I

2 MAX RIGID BARRIER

BETWEEN LOW-
VOLTAGE
COMPARTMENT AND

[---- T---/---
r
H IGH-VOLTAGE
- a - -
COMPARTMENT

D
Q-LOWEST HIGH-
VOLTAGE PHASE
CO" ECTOR
'
1
Q-LOWEST LOW-
VOLTAGE
TERMINAL E
I
i
I
L2 L MAX { BASE
PLANE

Separable Insulated Connectors with High-Voltage Ratings of

8.3 or 15.2 kV 21.1 and 21.1/36.6 kV
F (Note 4)
kVA F Figure 4 Figure 5
Ratings D E (Note 3) D E Interface Interface
75-150 21 21 18 27.0 21.0 24.0 30.0
225-500 27 31 18 27.0 31.0 24.0 30.0
750-2500 27 46 18 27.0 46.0 24.0 30.0

NOTES :
(1) High-voltage connector arrangements and dimensions are for applications requiring certain specific di-
mensions.
(2) All dimensions are in inches. Tolerance on Dimensions D and E is &OS inch.
(3) Transformers conforming to Figure 6, using 15.2kV connectors, require a minimum depth of 19.0
inches at the elevation at the parking stands.
(4) Dimensions are based on ANSI/IEEE 386-1985, Figures 7 and 8, interface for separable connectors.

Figure 7
Compartment Designations and Specific Dimensions
for Loop-Feed and Radial-Feed Transformers

22

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

LVA Ratings A B
75-150 5 6
225-2500 6 8

(a) Staggered Low- Voltage Terminal Arrangement

( b ) In-Line Low-Voltage Terminal Arrangement

NOTES:
(1) Low-voltage terminal arrangements and dimensions are for applications requiring
certain specific dimensions.
(2) All dimensions are in inches.
(3) Tolerance on all dimensions is t0.25 inch unless otherwise specified.
(4) Dimensions are to rigid barrier between high-voltage compartment and low-voltage
compartment.

Figure 8
Low-Voltage Terminal Arrangements
and Specific Dimensions

23

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

TT
t I
I
I
v 9(4) HOLES 5
TANK SURFACE TANK SURFACE
1
MIN 4
(NOTE 2)

kVA Low -Voltage kVA Low-Voltage

Ratings Ratings (volts) Ratings Ratings (volts)
75-300 208Y/120 500 208Y/120
75-500 240 75 0 240
75-5 00 480,48OY/217 750-1500 480,48OY/277

NOTES :
(1) All dimensions are in inches unless otherwise specified.
(2) Greater thickness may be required.
(3) Larger thread size or length, or both, may be required if materials other than
copper are used.
(4) Terminals a, b, and d are normally supplied; terminal c is supplied only when
specified.
(5) To be furnished with additional support, designed by the manufacturer, at the end
furthest from the tank wall without interfering with the use of any of the ten holes.

Figure 9
Low-Voltage Terminals

24

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD (257.1226-1987

I
I
-b TANK SURFACE
I I I
(NOTE 5)

\
I
- I , I -
'
1 ' _ ' I 1 I I
\ I , I , I

\) f I I
\ goo I I I I
Y
~~ ~

kVA Low-Voltage
Ratings Ratings (volts)
750-1000 208Y/120
1000 240
2000-2500 480,48OY/277

TANK S U R F A C E 7

kVA Low-Voltage Ratings Thread Size Minimum L

Ratings (volts) (Note 3) (Note 3)
75-150 240,208Y/120 5/8-11 UNC-2A 1.25
75-300 480,48OY/277 5/8-11 UNC-2A 1.25
225-300 240,208Y/120 1-14 UNS-2A 1.75
5 00 480,48OY/277 1-14 UNS-2A 1.75
500 240,208Y/120 1-114-12 UNF-2A 2.62

Figure 9
Low-Voltage Terminals (continued)

25

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

Figure 10
Angular Displacement

26

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.
 AMERICAN NATIONAL STANDARD C57.12.26-1987

+o.ooo
0'750 -0.025
o*86 -0.03

HEX HEAD 0.56

+o.oo
-0.02
PENTAHEAD

rO.380 MAX
0.226 M I N

-
-
- AS REQUIRED
AS REQUIRED =
4 1/2-13 UNC

0 . 1 2 5 7 r . 2 5 0 DIA
I I
MIN

Cross Section of Cross Section of

Recessed Nonrotating Cup - Recessed Nonrotating Cup -
Preferred Method Acceptable Alternative

:NOTES:
(1) All dimensions are in inches unless otherwise specified.
(2) The captive method is not shown.

Figure 11
Captive and Recessed Pentahead and Hex Head Bolts

27

Authorized licensed use limited to: Pan Electro Technic Enterprises Pvt. Ltd.. Downloaded on July 08,2010 at 10:26:35 UTC from IEEE Xplore. Restrictions apply.