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Disclosure to Promote the Right To Information
Whereas the Parliament of India has set out to provide a practical regime of right to
information for citizens to secure access to information under the control of public authorities,in order to promote transparency and accountability in the working of every public authority,
and whereas the attached publication of the Bureau of Indian Standards is of particular interest
to the public, particularly disadvantaged communities and those engaged in the pursuit of
education and knowledge, the attached public safety standard is made available to promote the
timely dissemination of this information in an accurate manner to the public.
!"#$%&# '(%)
“ !"# $ %& #' (")* &" +#,-. ”Satyanarayan Gangaram Pitroda
“Invent a New India Using Knowledge”
“ /0 )"1 &2 324 #' 5 *)6 ” Jawaharlal Nehru
“Step Out From the Old to the New”
“ 7"#1 &" 8+9&") , 7:1 &" 8+9&") ”Mazdoor Kisan Shakti Sangathan
“The Right to Information, The Right to Live”
“ !"# %& ;<" =7"#" > 72 &(: ?0 )"@" #AB 7" <&*" A *”Bhart+hari—N,ti-atakam
“Knowledge is such a treasure which cannot be stolen”
IS 3961-3 (1968): Recommended current ratings for cables,
Part 3: Rubber insulated cables [ETD 9: Power Cables]
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IS : 3961 (Part III) - l968(Reaffirmed 1996)
Indian Standard
RECOMMENDED CURRENT RATINGS FORCABLES
PART III RUBBER INSULATED CABLES
(Ninth Reprint AUGUST 1997)
UDC 62 1.31 5.21 :621 .315 .616
©Copyright 1968
BURE AU OF IND IAN STA NDA RD SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
Gr3 November 1968
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AMENDMENT NO. 1 SEPTEMBER 1983
TO
1 S : 3 9 6 1 ( P a r t 3 ) - 1 9 6 8 RECOMMENDED CURRENT
RATINGS FOR CABLES
PART 3 RUBBER INSULATED CABLES
A l t e r a t i o n
[Page 5, clause 3.1, entry(b), under second col.]Substitute 'Clipped direct and unenclosed' for
'Clipped direct and enclosed'.
(ETDC 59)
Peprint at Printograph, New Delhi, Ph : 5726847
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IS : 3961 (Part III) - l968
Indian Standard
RECOMMENDED CURRENT RATINGS FORCABLES
PART III RUBBER INSULATED CABLES
Conductors and Cables Sectional Committee, ETDC 32
Chairman
SHRI K. MATTHAN
Members
SHRI S. D. BANA
SHRI J. H. PATEL ( Alternate)SHRI P. K. BHARUCHA
SHRI A. C. MODY ( Alternate)SHRI M. R. BHAT
SHRI B. C AMIN ( Alternate)WG CD R H. S. BHATIA
Ripresenting
Tata-Ebasco Consulting Engineering Service*, Bombay
Gujarat Electricity Board, Baroda
Insurance Association of India, Bombay
Bombay Suburban Electric Supply Ltd, Bombay
Directorate of Technical Development & Product ion(Air)
Fo O F F R S. V. BASARKAR ( Alternate)SRRI D. P. BHATIA
SHRI P. L. KAPUR ( Alternate)SHRI S. K. BHATTACHABYA
SURVEYOR OF WORKS II
(ELECTRICAL) ( Alternate)
SHRI H. K. BHATTACHARJEE
SHRI N. K. SEN ( Alternate)SHRI N. N. CHAKRABORTI
SHRI K. V. CHAUBAL
SHRI M. L. DONGRE
SHRI AVTAR SINGH ( Alternate)CDR N. G. FADNAVIS
SHRI HARNAM SINGH
SHRI S. K. M A N I ( Alternate)SHRI A. K. KAHALI
SHRI N. V. RAMAN ( Alternate)SHRI S. K. KANJILAL
SHRI S. T. UDESHIR ( Alternate)
Directorate General of Supplies & Disposals (Inspec-
tion Wi ng) (Ministry of Works, Housing &Supply)
Central Public Works Department
Directorate General of Mines Safety (Ministry ofLabour, Employment & Rehabilitation)
Electrical Inspector to the Government of WestBengal, Calcutta
Federation of Electricity Undertakings of India.Bombay
Bombay Electric Supply & Transport Un de rt ak in gBombay
Naval HeadquartersDirectorate of Standardization (Ministry of Defence)
Indian Cable Co Ltd, Calcutta
Railway Board (Ministry of Railways)
(Continued on page 2)
BUREA U OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
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IS : 3961 (Part III) - l968
(Continued on page 1)
Members
SHRI D.M. LAM
Divisional Engineer Tele-
GRAPHS (C) ( Alternate)SHRI M. R. LODH
Representing
Indian Posts & Telegraphs Department (Ministry ofTransport and Communications)
Devidayal Cable Industries Ltd, BombaySHRI KAMAL AGGARWAL ( Alternate)
SHRI O. P. MATHURSHRI A. K. MITRA
SHRI P. S. SRINIVASA MODALIAR
Electrical Manufacturing Co Ltd, CalcuttaCalcutta Electric Supply Corporation Ltd, CalcuttaRadio & Electricals Manufacturing Co Ltd. Bangalore
SHR I V. R. CHANDER SHRI
SHBI S. N. MUIHUI National Tot House, CalcuttaSHRI B. K. MURHKRJRR ( Alternate)
SHRI P. MUKUNDAN
SHRI R. SRN ( Alternate)SHRI H. V. NARAYANA RAO
Hindustan Cables Ltd, Rupnarainpur
Central Water & Power Commission (Power Wing)SHRI S. S. MURTHY ( Alternate)
SHRI S. PEER MOHAMMADSHRI P. M. JOSEPH ( Alternate)
SHRI S. R. C. POTISHRI K. S.JOSHI ( Alternate)
SHRI B. H. RAISHRI J. S. BHAN ( Alternate)
SHRI A. K. RAMANSHRI P. K. SANKARANARA-
YANAN ( Alternate)SHRI M. J. RAO
Aluminium Industries Ltd, Kundara
Oriental Power Gables Ltd, Kota
National Insulated Cable Co of India Ltd, Calcutta
Asian Cables Corporation Ltd, Bombay
Tata Hydro-Electric Power Supply Co Ltd, BombaySHRI M. V. GONDHALEKAR ( Alternate)SHRI G. P. SAXENA
SHRI L. K. SINGHI ( Alternate)DR P. S. SHAHSHRI K. SRIKIVASA RAO
SHRI A. SUBRAMANIAM
Fort Gloster Industries Ltd, Calcutta
Cable Corporation of India Ltd, BombayDirectorate General of Technical Development
(Ministry of Works, Housing & Supply)Madras State Electricity Board, Madras
SHRI A. T. SRESHTA ( Alternate)SHRI L. R. SUBRAMANYAM Henley Cables (India) Ltd, Poona
SHRI K. V. RAMA RAO ( Alternate)SHRI Y. S. VENKATSEWARAN,
Director (Elec tech) (Secretary)Director General, ISI ( Ex-officio Member )
Panel for Current Ratings of the Different
Types of Cables, ETDC 32: P5
Members
SHRI P. M.Joseph Aluminium Industries Ltd, KundaraSHRI S. KRISHNAMOORTHY ( Alternate)
SHRI H. V. NARAYANA RAO Central Water & Power Commission (Power Wing)SHRI S. S. MURTHY ( Alternate)
SHRI N. V. RAMANSHRI M. DEV ( Alternate)
SHRI P. K. SANKARANARAYANANDR P. S. SHAH
Indian Cable Co Ltd, Calcutta
Asian Cables Corporation Ltd, BombayCable Corporation of India Ltd, Bombay
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IS : 3961 (Part III) - l968
I ndian Standard
RECOMMENDED CURRENT RATINGS FOR
CABLES
PART III RUBBER INSULATED CABLES
0 . F O R E W O R D
0.1 This Indian Standard (Part I I I ) was adopted by the Indian StandardsInstitution on 16 July 1968, after the draft finalized by the Conductors andCables Sectional Committee had been approved by the ElectrotechnicalDivision Council.
0.2 This standard has been drawn up to provide to the users generalguidance for loading of cables. The overloading of cables will reduce thelife expectancy of the cable and at the same time underloading it will meanuneconomic utilization of its capacity. Depending upon the loading cyclemet with in practice, the installation engineer may decide the economicloading of cables.
0.3 The permissible current ratings have been specified for three commonlyadopted conditions of installation, namely, bunched and enclosed, clippeddirect and un-enclosed and other defined conditions.
0.4 The rating factors specified in 4 shall be used to modify the currentratings in respect of ambient temperature and grouping.
0.5 This standard is being issued in a number of parts covering different
types of cables. Other part i published so far are:IS:3961 (Part IU1967 Recommended current ratings for cablet:
Part I Paper-insulated lead-sheathed cable:
IS:3961 (Part II)-1 967 Recommended current ratings for cablet:Part II PVC-insulated and PVC sheathed heavy duty cables
IS:3961 (Part IV)-1968 Recommended current ratings for cables:Part IV Polythene insulated cables
IS:3961 (Part V)-1968 Recommended current ratings for cables:Part V PVC-insulated light duty cables and wires
0.6 In preparing this standard, assistance has been derived from IEERegulations for the Electrical Equipment of Buildings of Institution of theElectrical Engineers, U. K.
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IS : 3961 (Part III) - l968
0.7 For the purpose of deciding whether a particular requirement of thisstandard is complied with, the final value, observed or calculated, express*ing the result of a test, shall be rounded off in accordance with IS: 2-1960*.
The number of significant places retained in the rounded off value shouldbe the same as that of the specified value in this standard.
1. SCOPE
1.1 This standard (Part I I I ) covers recommended current ratings for boththe copper conductored as well as aluminium conductored rubber insulatedcables of voltage ratings 250/440 volts and 650/1100 volts covered by
IS: 434 (Part I) -1964† and IS: 434 (Part II) - 1964‡ respectively.2. BASIC ASSUMPTIONS
2.1 The current ratings given in Tables 1 and 2 of the standard are basedon the following assumptions:
a)
b)
Ambient air temperature
Maximum conductor temperature
40°C
60°C
3. METHOD OF INSTALLATION
3.1 The current ratings given in this standard are for the methods of installation as given in the following table:
Type of Cable
Single-core cables
Type of Installation
a) Bunched and enclosed
b) Clipped direct andun-enclosed
c) Defined conditions
a)
b)
a)
b)
a)
Method of Installation
2 cables, single-phase
ac or dc
3 or 4 cables, three-phase ac
2 cables, single-phaseac or dc
3 or 4 cables, three-
phase ac
Flat or vertical (2cables, single-phase acor dc, or 3 or 4 cables,three-phase)
*Rules for rounding off numerical values (revised ).
†Sperification for rubber insulated cables: Part I With copper conductors (temmi).‡Specification for rubber insulated cables Part II With aluminium conductors
(revised ).
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IS : 3961 (Part III) - l968
Type of Cable
Twin and multi-core
cablesa)
b)
c)
Type of Installation
Enclosed in a conduit
or trunking
Clipped direct andenclosed
Defined conditions
b)
a)
b)
a)
b)
c)
d)
a)
b)
Method of Installation
Trefoil (3 cables,
three-phase)One-flat twin cable,single-phase ac or dcOne-flat three-corecable, three-phase
One-flat twin cable,single-phase ac or dc
One-flat three-corecable, three-phase
One-circular twin
cable, single-phase acor dcOne-circular three- orfour-core cable, three-phase
One-circular twin
cable, single-phase acor dcOne-circular three-
core cable, three-phase
4. RATING FACTORS
4.1 For Variation in Ambient Temperature — The current ratings forcables given in Tables 1 and 2 are based on an ambient air temperature of40°C. Where the ambient air temperature differs .from this value, theappropriate rating factor given below shall be applied:
Ambient Temperature°C
25
30
35
45
50
55
Rating Factor
1.32
1.22
1.12
0.86
0.71
0.50
4.2 For Groups — The current ratings given in Tables 1 and 2 are for
tingle circuits only. For groups, the appropriate rating factor given in 4.2.1shall be applied.
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IS : 3961 (Part III) - l968
4.2.1 For groups of cables* (o r circuits†) un-enclosed, the single-circuitratings apply provided that:
a) the horizontal clearance between cables* (or circuits†) is:1) For Single-Core Cables
i)
ii)
not less than 6 times the overall diameter of an individual
cable, and
not less than the overall width of an individual circuit, exceptthat the horizontal clearance need not in any case exceed150 mm.
2) For Twin and Multi-core Cables
not less than b times the overall diameter of an individual
cable except that the horizontal clearance need not in any caseexceed 150 mm.
b)
c)
the vertical clearance between cables* (or circuits!) is not lessthan 150 mm; and
if the number of cables* (or circuits†) exceed 4, they are installedin a horizontal plane.
In all other cases, unless a more precise evaluation of current rating hasbeen made , based on experimental work or calculated data, the followingfactors are applicable:
Rating Factor for Number of Cables* (or Circuits†) [Pair ofcables in single-phase ac or dc; 3 cables per circuit or 4 cables(three-phase + 1 neutral) per circuit ]
Single-core cable
Twin and multi-core cablet
20.80
0.80
30.69
0.70
40.62
0.65
50.59
0.60
60.55
0.57
80.51
0.53
100.48
0.48
120.43
0.45
140.41
0.43
16‡0.39
0.41
18‡0.38
0.39
20‡0.36
0.38
5. DEFINED CONDITIONS
5.1 The current ratings in the columns of the tables headed ' defined condi
tions' apply to cables run under the conditions defined below.5.1.1 Single-Core Cables
5.1.1.1 Two or three single-core cables are installed one above theother, fixed to the vertical surface of a wall or open cable trench as follows,the distance between the wall and the surface of the cable being 25 mm ineach instance:
a) Cables in which the conductor cross-sectional area does not exceed185 mm
2 are installed at a distance between centres of twice the
overall diameter of the cable,
*For twin and multi-core cables.†For single-core cables,‡In case of single-core cables, not applicable to three-phase.
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IS : 3961 (Part III) - l968
b)
c )
Cables in which the conductor cross-sectional area exceeds 185 mm2
are installed at a distance between centres of 90 mm, and
The ratings for two cables may be applied with safety in instances
where such cables are installed in horizontal formation on bracketsfixed to a wall, either spaced as indicated above, or touchingthroughout.
5.1.1.2 Three single-core cables are installed in trefoil formation, fixedto the vertical surface of a wall or open cable trench, the cables touchingthroughout and the distance between the wall and the surface of the nearestcable being 25 mm; or alternatively, three single-core cables are installedin a trefoil formation and laid on a non-metallic floor, the cables touchingeach other and the floor throughout.
The ratings given apply provided that the sheaths of single-core metal-sheathed cables are electrically bonded at each end of the run.
The cables are assumed to be remote from iron, steel, or ferro-concreteother than the cable supports.
5.1.2 Multi-care Cables — Gables of all types other than single-core cablesare installed singly fixed to the vertical surface of a wall or open cabletrench, the distance between the surface of the cable and the wall being25 mm in every instance.
For cables spaced by distances less than those described above, thecurrent ratings in the columns headed ' clipped direct' to a surface shouldbe applied.
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IS : 3961 (Part III) - 1968
T A B L E 1
C U R R E
N T R A T I N G S F O R
S I N G L E - C I R C U I T S I N G L E - C O R E R U B B E R
I N S U L A T
E D S H E A T H E D
O R
U N S H E
A T H E D
U N A R M O U R E D
C A B L E S A C C O R D I N G
T O
I S : 4 3 4 ( P a r t s I &
I I ) - 1 9 6 4
( C l a u s e s 2 . 1 , 4 . 1 a n d
4 . 2 )
N O M I N A L
A R E A
O F
C O N D U C T O R
( 1 )
m m
2 1 1 . 5 2 . 5 4 6 1 0 1 6 2
5 3 5 5 0 7 0 9 5 1 2 0 1 5 0 1 8 5 2 2 5 2 4 0 3 0 0 4 0 0 5 0 0 6 2 5
B U N C
H E D
A N D
E N C L O S E D
2 C a b l e s , S i n g l e -
P h a s e
a c o r d c
C u
( 2 )
A 1 1 1 4 1 8 2
4 3 1 4 2 5 7 7 3 8 8 1 0 8 1 3 3 1 6 4 1 9 0
— — — — — — — —
A l
( 3 )
A 8 1 1 1 4 1
9 2 4 3 2 4
5 5 6 6 9 8 4 1 0 3 1 2 7 1 4 7
— — — — — — — —
3 o r 4 C a b l e s ,
T h r e e - P h a s e a c
C u
( 4 ) A
9 1 2 1 5 2 1 2 5 3 6 4 9 6 2 7 5 9 3 1 1 4 1 3 9 1 6 1
— — — — — — — —
A l
( 5 )
A 7 9 1 2 1
6 2 0 2 8 3 8 4 8 5 8 7 2 8
8 1 0 8 1 2 5
— — — — — — — —
C L I P P E D
D I R E
C T
A N D
U N - E N C L O S E D
2 C a b l e s , S i
n g l e -
P h a s e a c o r d c
C u
( 6 )
A 1 3 1 7 2 2 2 9 3 7 5 1 6
8 8 8 1 0 7 1 3 1 1 6 1 1 9 6 2 2 4 2 5 7 2 9 3 3 3 1 3 4 4 4 0 0 4 8 8 5 7 0 6 5 5
A
l
(
7 ) A 1 0 1 3 1 7 2 2 2
8 3 9 5 3 6 8 8 3
1
0 2 1 2 4 1 5 2
1
7 4
1
9 9
2
2 7
2
5 7
2
6 6
3
1 0
3
7 8
4
4 2
5
0 7
3 o r 4 C a b l e s ,
T h r e e - P h a s e a c
C u
( 8 ) A 1 1 1
5 2 0 2 7 3 4 4 6 6 2 7 9 9 6 1 1 8 1 4 3 1 7 6 2 0 3 2 3 0 2 6 4 2 9 7 3 1 0 3 6 0 4 3 8 5 1 3 5 9 1
A l
( 9 ) A 9 1 2 1 5 2 1 2
6 3 6 4 8 6 1 7 5 9 1 1 1
1 1 3 7 1 5 7 1 7 9 2 0 5 2 3 0 2 4 0 2 7 9 3 3 9 3 9 8 4 5 8
D E F I N E D
C O N D I
T I O N S [ F L A T
O R
V E R T I C A L
( 2
C A B L E S ) , S I N G L E
-
P H A S E
a c O R d c
,
O R 3 O R 4 C A B L E S
,
T H R E E - P H A S E ]
C u ( 1 0 )
A — — — — — — — — — 1 3 8 1 7 3 2 1 8 2 5 5 2 9 4 3 3 7 3 8 5 4 0 1 4 7 9 5 7 5 6 5 6 7 4 6
( A l
1 1 )
A — — — — — — — — — 1 0 7 1 3 4 1 6 9 1 9 7 2 2 8 2 6 2 2 9 9 3 1 1 3 7 2 4 4 5 5 0 9 5 7 8
T R E I L
T H R E E -
P H A S E
I
C u ( 1 2 )
A — — — — — — — — — 1 2 5 1 5 3 1 8 9 2 2 0 2 5 3 2 9 0 3 2 8 3 4 2 4 0 5 4 8 3 5 6 1 6 3 1
A l
( 1 3 )
A _ — — — — 9 7 1 1 9 1 4 7 1 7 0 1 9 6 2 2 4 2 5 4 2 6 5 3 1 4 3 7 8 4 3 5 4 8 9
8
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IS : 3961 (Part III). 1968
T A B L E 2
C U R R
E N T R A T I N G S F O R S I N G L E - C I R C U
I T T W I N
A N D
M U L T I - C O R E R U B B
E R I N S U L A T E D
S H E A T H E D
O R
U N S H E A T H E D
U N A R M O U R E D
C A B
L E S A C C O R D I N G T O
I S : 4 3 4 ( P a r t s I &
I I ) - 1 9 6 4
( C l a u s e
2 . 1 ,
4 . 1 a n d 4 . 2 )
9
N O M I N A L
A R E A
O F
C O N D U C
T O R
( 1 )
m m 2
1 1 . 5 2 . 5 4 6 1 0 1
6 2 5 3 5 5 0 7 0 9 5 1 2 0 1 5 0 1 8 5 2 2 5 2 4 0 3 0 0
E N C L O S E
D
I N
C O N D U I T
O R
T R U N K I N G
O n e - F l a
t
O n e - F l a t 3 -
T w i n C a b
l e ,
S i n g l e - P h a s e
a c o r d c
C u
( 2 ) A 1
0 1 3 1 7 2 3 2 9 3 9 5 3 6 7 — — — — — — — — — —
A
l
( 3
)
A
8 1 0 1 3 1 8 2
2 3 1 4 1 5 2 —
—
—
—
—
—
—
—
—
—
C o r e
C a b l e ,
T h r e e - P h a s e
C u
( 4 ) A
9 1 1 1 5 2 0 2 5 3 4 4 7 6 0 —
— — — — — — — — —
A l
( 5 ) A
7 9 1 1 1 7 2 0 2 7 3 6 4 6 —
— — — — — — — — —
C L I P P E D
D I R E C T
A N D
U N - E N C L O S E D
O n e - F l a t
T w i n C a b l e ,
S i n g l e - P h a s e
a c o r d c
t C u
( 6 )
A 1 2 1 5 2 0 2 7 3 4 4 6 6 2 7 9 —
— — — — — — — — —
A l
( 7 ) A 9 1
2 1 6 2 1 2 6 3 6 4 6 6 1 —
—
—
—
—
—
—
—
—
— —
—
—
—
— —
— O n e - F l a
t 3 -
C o r e C a b l e ,
T h r e e - P h a s e
C u
( 8 )
A 1 0 1 4 1 8 2 4 3 0 4 0 5 7 7
0 —
—
- -
A l
( 9 )
A 8 1 1 1 4 1 8 2 3 3 1 4 3 5 4 —
— — — — — — — — —
O n e - C i r c u l a r
i : T w i n C a b l e ,
S i n g l e - P h a s e
a c o r d c
C u
( 1 0 ) A 1
0 1 3 1 8 2 3 3 0 4 1 5 5 7 0 8 6 1 0 9 1 2 8 1 5 7 1 8 0 2 0 5 2 3 4 2 6 4 2 7 5 3 1 9
I
A l
( 1 1 ) A
8 1 0 1 4 1 8 2 3 3 2 4 3 5 4 6 6 8 4 1 0 0 1 2 1 1 3 9 1 5 9 1 8 1 2 0 5 2 1 3 2 4 7
O n e - C i r c u l a r
3 o r 4 C o r e
C a b l e , T h r e e -
P h a s e
C u
( 1 2 )
A 9 1 2 1 6 2 1 2 6 3 6 4 8 6 1 7 5 9 2 1 1 2 1 3 7 1 5 7 1 7 8 2 0 4 2 3 1 2 4 0 2 8 0
A l
( 1 3 )
A 7 9 1 2 1 6 2 0 2 8 3 7 4 7 5 8 7 1 8 7 1 0 6 1 2 3 1 3 8 1 5 8 1 7 9 1 8 6 2 1 7
D E F I N E D
C O N D I T I O N S
O n e - C i r c u l a r
T w i n C
a b l e ,
S i n g l e -
P h a s e
a c o r
d c
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BUREAU OF INDIAN STANDARDS
Headquarters :Manak Bhavan, 9 Bahadur Shah Zafar Marg, NEW DELHI 110002Telephones: 323 0131, 323 3375, 323 9402Fax: 91 11 3234062, 91 11 3239399, 91 11 3239362
Telegrams: Manaksanstha
(Common to all Offices)Central Laboratory :
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Ragional Offices:
Central: Manak Bhavan, 9 Bahadur Shah Zafar Marg, NEW DELHI 110002
* Eastern : 1/14 CIT Scheme VII M, V.I.P. Road, Manlktola, CALCUTTA 700054
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Southern : C.I.T. Campus, IV Cross Road, CHENNAI 600113
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Telephone
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337 86 62
60 38 43
235 23 15
832 92 95
550 13 48
839 49 55
55 40 21
40 36 27
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8-28 88 01
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