IS 8945 (1987): Electrical measuring instruments …electrical measuring instruments shall be not only constructed in accordance with Group I require- ments, but shall also be submitted

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IS 8945 (1987): Electrical measuring instruments forexplosive gas atmospheres [ETD 12: Measuring Equipment forBasic Electrical Quantities]

IS : 8945 - 1987

Indian Standard

SPECIFICATION FOR '-\ I ELECTRICALMEASURINGINSTRUMENTS \, / FOREXPLOSIVEGASATMOSPHERES

( First Revision )

UDC 621-317.7-213-34

, -. ‘.

..’

i @ Cojyright 1988

BUREAU OF INDIAN STANDAnRDS MANAK BHAVAN, Y BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

June 1988

IS : 8945 - 1987

Indian Standard

SPECIFICATION FOR ELECTRICAL MEASURING INSTRUMENTS

FOR E’XPLOSIVE GAS ATMOSPHERES

( First Revision )

0. FOREWORD

0.1 This Indian Standard ( First Revision ) was adopted by the Bureau of Indian Standards on 8 .January 1988, after the draft finalized bv the lilectrical Measuring InstrumL-nts Sectional kom- mittee had ‘been approved by the ElectrotcAmical Division Councrl.

0.2 This standard sprcihzs the ,general rcquirc- mt:nts for construction testing and marking of rleccrical apparatus for esplosive gas atmospheres and to be read with the followmg Indian Stand- ards concerning specific types of protection:

IS

IS

IS

: 2148-1981 Specification for flameproof enclosures of electrical apparatus ( second revision )

: 5780-1980 Specification for intrinsically safe electrical apparatus and circuits (,first 1zuisiom )

: 6381-19'72 COn~trllcticJn and testing of electrical apparacu~ with type of protection ‘e’

IS : 7389 ( Part 1 )-1976 Spkfication for prcssrlrizctl er:c:oilll (’ Vi:11 110 internal

snurce of flammab!e gas or vapour (,/irsl reui.ciort )

IS : 8289-1976 Specification ro, f~l(~ctrical equipment with type of’ protrction ‘11’

0.3 For the purpose of this standard, \vlicrcvc*r th(-rc is relcrcnce to other stanr!;u d(s), Iatrsl version of the referred standard(s) Fliall b<. apl)licablr.

0.4 While preparing this standard, assistaricc bar been derived from all parts of IEC Pull 79 ‘Electrical apparatus for explosive gas atmos- phere’ issued by the International Electrotechnical Commission.

0.5 For the purpose of deciding whether a [J~Wfi-

cular requirement of this standard is cornl)lic:tl witll, the final value, observed or calclilatcd, expressing the result of a test, shall I)i- ro~md(~~1 011 in accordance with 1.S : 2-1960*. ‘I’hcb nllr~li~(.r 01 significant places retained in the rorirrtlt:tl 00 v:rlrkc* should be the same as tllat of the. SIJKifie(~ I.:LIIIT

irl this standard.

1. SCOPE

1.1 This st;mtla~d CI :VC’TS rc.qliirexriellts and tests tE)r ti,(. fiJilOwing direct ac,tinc; electrical indicating i!i~tI‘~!lilrll1S ( . ‘1 111~ uding multirnn~e instruments ) t;)r u;e in l~azarr!ou; ;irn;-splicre5:

2) A 11i1i f‘tm-5.

i,’ \Voltrnc.tcrs.

c) CVattnIctr! i ' c:ir:c:f= and polypha5c ’ ,

c’: \‘a1 nlclcI’\ ~ 1

c.,j Power factor iriilicntol~~,

f ) Frequency’ meters ( pointer and vibrating reed type ), and

g) Ohmmeters ( non-ratio type j.

IS : 8945 - 1987

definitions in addition to those given in IS : 5572 ( Part 1 )-1970* and IS : 2148-1968t, shall apply.

2.1 Flameproof Enclosure - An enclosure for electrical instrument that will withstand, when the covers or other access doors are properly secured, an internal explosion of the flammable gas or vapour which may enter or which may originate inside the enclosure, without suffering damage and without communicating the internal flammatlon ( or explosion ) to the external tlammable gas or vapour in which it is designed to be used through any jolrlts or other structural openings in the enclosure.

2.2 Plate Protection - The type of protection in which the parts capable of igniting flammable mixtures are enclosed in an enclosure having openings with special fittings ( plate protection stacks ) such that, in case of an internal explosion, a dmg~~ous pressure rise is avoldcd and transmls- sion 01 the explosion to the flammable mixture outside the enclosure is prevented.

2.3 Pressurized Enclosure - An enclosure for instruments in which the parts are capable of igniting Hammable or explosive mixture: are enclosed in enclosures, which are scavenged by fresh air or inert gases ( protective gas ) under pressure so that fire damp or explosrve mixture which have eutered the enclosure before the apparatus was put into operation are expelled and may not enter the enclosures during operation.

2.4 Intrinsically-Safe Circuit - A circuit in which any spark or thermal effect produced either normally or in specified fault conditions is incapable, in the test conditions prescribed in this standard, of causing ignition of a given gas or vapour.

2.4.1 Intrinsically-Safe Apparatus - Apparatus in which all the circuits are mtrinsically safe.

2.5 Special Fastenings - Fastenings which may only be opelled with special means ( for example, triangular shrouded bolt ).

2.6 Creepage Distance - The shortest path by which a curlent may pass over the surface of‘ an insulator or through joints of insulators joined together.

2.7 Clearance -- ‘The sllortest path in air as mca,;urcd by a taut string, over which current may pass ( Ilasliover ).

2.8 Limiting Temperature - 1 t is the maximum perlr!issilJlt~ ct?11prr:?ture ot apparatus 01 pal ts of apparatus. It is determined by the:

a) tlaIlgt:I of ignition of the explosive gas atmosphere, and

b) thermal stability of the materials used.

The lower temperature is the one to be taken into consideration.

2.9 Ignition Temperature - The lowest tem- perature at which ignition occurs under specified test conditions.

2.10 Maximum Surface Temperature - The highest temperature attained under practical con- ditions of operation withm the rating of the appa- ratus ( and recogmzed overloads, ii any ) by any part ot’any surface, the exposure of which to an explosive atmosphere may involve a risk.

XUTE --For flameproof apparatus, the, surface, to IN considered is the exttrnal surface. I“ur other t)ppr 01 apparatus intclrxil surfaces are tqualiy inlporr,mt, 11 the exploiive atmosphere has access to ~hern.

2.11 Spacings - The shortest distance between two reference points irrespective of the mate1 ial between them ( air, oil, compound ).

NUTE - Creepage distance, clearance and spacing5 occur between:

a, I ive parts at ditferent L oltages,

bj live parts and earthed parts,

c) hve parts and pomrs accearible to culltact 01 metal parts, an0

d) live parts and supports ( walk, etc J.

When determining crerpage distances, clcarar~ct and spacmgs, it ahoulu be norrd that live parts which are only varntshed, enamelled, oxidlzcd or surface-rrmt- ed in a sm111~~r manner are not conslde~ed ah Insulate (I.

2.12 Type of Protection ‘e’ - The type of pro- tection ‘e’ is the method ot protection by wluch additional measures are apphed, so as to g~vc increased security against the possibility oi exccb- sive temperatures and of’ the occurrence ot arcs and sparks in apparatus which does not pr~~ducc arcs or sparks in normal service.

2.13 Thermal Current Limit Ith - ‘Ihe IL~IS value ot currcut wliich may flow through 1~‘” 101 one second wirhout causing excessive Ilealnlg.

2.14 Dynamic Current Limit fd3.,, - ‘l’he pc-ilk value ot the current, the forces due to whch thr electrical apparatus may wiLtistarld \L lllI( IUI damage.

3. GROUPING AND CLASSIFICATION OF ELECTRICAL MEASURING INSTRUMENTS

3.1 Llec tric;tl ~~i(';huriiJfi instruinl.lJti loI t.xplo\l\ I’

2

gas atmospheres is divided into ( see IS : 2148-1981* ): ’

Group I - Electrical measuring instruments for mines susceptible to fire-damp.

Group II - Electrical measuring instruments for all places with an explosive gas atmos- phere, other than mines susceptible to fire- damp.

3.1.1 For mines where gases other than fire- damp may normally and naturally occur, the electrical measuring instruments shall be not only constructed in accordance with Group I require- ments, but shall also be submitted to the tests prescribed for the appropriate Group II explosive mixture and marked accordingly.

3.2 Electrical measuring instruments of Group II is subdivided according to the nature of the explosive gas atmosphere for which it is intended.

3.2.1 For certain types of protection, the sub- division IIA, IIB, IIC is prescribed; this is based on the maximum experimental safe gap (MESG) for flameproof enclosures or on the minimum igniting current (MIC) for intrinsically sare elec- trical measuring instruments (see IS : 9570-1980t).

NWI.E - Measuring instruments marked IIB is suitable for applications requiring Group IIA measuring instruments. Similarly, measuring instruments marked IIC is suitable for applications requiring Group IIA and Group IIB measuring instruments.

3.2.2 For all types of protection, the tempera- ture classes II to 76 correspond to the classilica- tion of electrical apparatus according to its maximum surface temperature ( see Table 1 ).

3.3 Electrica! measuring instruments may be tested for a particular explosive gas atmosphere. In this case it shall be certified and marked accordingly.

4. TEMPERATURE

4.1 Electrical measuring instruments for explosive gas atmospheres shall normally be designed for operation in an ambirnt temperature range from - 2V’C to + 40°C. Where the electrical measuring instruments is suitable for a temperature range \vhi~~Il difl’ers from tllis, the range shall be marked accordingly. The temperature classification, ‘ 7’ class as given in Table 1, shall be based on the maxil~lum trmprrarurc of tlic ambient tempera- tlu-e rarlge for which the measuring instruments is designed.

4.2 The maximum surface tcrupcr,lture shall not (.xcf‘<.(I:

a\ for Group I clcctrical Itieasuring instru- ments;

IS:8945-1987

1) 90°C where instruments are likely to be touched in normal use,

2) 135°C if the above risk is avoided, that is, instruments are not likely to come in contact with the personnel directly.

b) for Group II electrical rneasuring instru- ments; the value in Table 1 bvhich corrc’s- ponds to the temperature class of the

electrical measuring instruments.

NOTE - When chasing electrical mvasuring instru- ment> the Group II, the user should take into accollnt the influence and the smouldcring t(‘mperatuw of dust\ if they arc likely to be deposited 111 a la),‘r.

TABLE 1 CLASSIFICATION OF MAXIMUM SURFACE TEMPERATURE FOR GROUP II ELECTRICAL MEASURING INSTRUMENTS

( Claues 3.2.2, 4.1, 4.2 and 4.3)

Temperature class 71 72 73 74 75 Ifi

Maximum surface 450 300 200 135 1 uo 8.5 remperature

t”(J)

4.3 For Group II electrical measuring instruments, if a maximum surface temperature different from those given in Table 1 is selected, this ternpera- ture shall be indicated on the electrical measuring instruments concerned.

4.4 The maximum surface temperature of ttlc electrlcal measuring iustrumcnts shall be below the lowest ignition temperature of the explosive gas atmospheres for which the electrical measuring instrument is designed. However, f’or cumpouents having a total surface area of not more than 10 cm% ( for example, transistors or resistors used in intrinsically safe electrical circuits ), thrir surface temperature may rxceed that fur the t(m- perature class marked vn the electrical mc,asuring instruments if there is no direct or indirect risk 01 ignition from these components with safety margin Of:

a) 50°C for 7-1, 7-2 and 73; and

b) 25% for l-4, irg and 7-6.

‘l‘his safety n,argiri sllnll l)e cnsurcd l)y caspcri- ence of similar co~rlpon(~t~ts or 1)~ test 01 ttlc elrctriLa1 measurill g Iu~trumeiits it>cxif ill c,ul)losivc IllixLurcs having tile apl)I~opr~a~c tllcrrl~~ll ‘:;.;~t~ori c1i.lr~ic.teristic.s ( see IS : U~:i!~-l!~/O” j.

5. TYPES OF PROTECTION

3

IS : 8945 - 1987

either one or combination of the following types of protection:

a) Intrinsically safe electrical instrument,

b) Pressurized enclosure,

c) Flameproof enclosure,

d) Type of protection ‘e’, and

e) Plate protection ( flame arrestor ).

6. GENERAL CONSTRUCTIONAL REQUIREMENTS

6.1 General - In addition to the requirements specified in relevant part of IS : 12+8*, the follow- ing requirements given in 6.1.1 to 6.2.4.7 shall be complied.

6.1.1 Electrical instruments shall be able to withstand the special conditions and fulfl the: requiremrnts of mirling service ( for exampI<:. rough handling, illTVC't 01' moistul~c, p(iL-if!.irrg agtnts :Ind clusl, tcrilprr,lture diKcrences, Ctc ).

6.1.2 Tllc. design of clectri:,:ll irlstrumc~nt\ fat u<~’ in pxplosivc sits atmosp1lcre s11ould be based or? ill, am!)i(::it tcnlprralu~~e Of‘ l(J”(:;

6.1.3 Mea-ltrirlg instruments shall nr)t be installed in the housing of circuit breaker provided lvith ‘171arneproof Enclosure’ or ‘Plate Protection’.

6.2 Additional Requirements

6.2.1 Intrir~sicaUpSafe Iutrument - An intrinsi- c,illv-safe instrument req;irernents:

shall satisfy three basic

a) Adequatr separation from other ci: cldits,

b) Ali components in the circuit shall have a maximum surface tempcratnre less t!lan specitied in 1s : 5780-19801_ in order to avoid igrlition resultin,? from thermal effect, and

c) No ignition due to spark shnll result when tile circuit is tested or checked.

6.2.1.1 In all other respects the instrument sil:~ll satlsfb. tl:c: reqilircments uf IS : ~~5SO-l%Oi-.

6.2.2.3 Pressurizing system shall be so arranged that, until a quantity of scavenging medium ( air tir inert gas ) equal to five times the capacity of the enclosure has been passed through it, the electrical parts which might ignite the explosive mixtures cannot be put into operations.

6.2.2.4 If scavenging stops, the parts inside the enclosures which might ignite the rxplosivc. mixture should be put out of service or an alarm signal should be given.

6.2.2.5 To take care oI’ static charge, all electrically conducting metal parts shall br properly earthed.

6.2.3 FLameproof Enclosure - The provisions of IS : 21J8-1981* shall apply.

6.2.4 T_:pe oj- Protection ‘e’

6.2.4.1 The Ijrovisions of IS : 6X81-1972t sh?ll a!!pl!~,

6.2.4.2 hIc,ksurill;r instrunlrnts and measul.- iilg transf0rnicr.s sli;li! be able to \v,tlistdl!d cc,rltinuousiy 1 ,I! tir;lc._; tilrir ratctl currelit I, 01 their rated voltage \vithout excerding the, limitill: ternpcl ature speci liczd III ‘l‘ablc 1.

6.2.4.3 Current transformers and thr currc‘nt carrying parts of measuring instruments ( cxclutl- ing voltage circuits ) shall be able to withstand thermal and mechanical stresses resulting from currents at least equal to the values stated in Table 2, with no reduction irl their security against explosions.

TABLE 2 RESISTANCE TO THE EFFECT OF SHORT-CIRCUIT CURRENTS

4

to equal to the current flowing in the short- circuited secondary windings of the current trans- formers with its primary windings carrying the currents Zth and Zdyn applicable to them ( Zdyn is the dynamic current limit. )

6.X4.6 Instruments with moving coils are not permitted.

6.2.4.7 If the current is fed to the moving part through strips, the stated voltage and current limit shall not be exceeded even in the case of contact with the frame or short circuit between strips.

a)

b)

d)

Type of protection ‘e’ may be applied to main supply apparatus provided at all loads (from no load to short circuit ), the tempe- rature and the temperature rise do, s not exceed the value given in Table 1.

Instruments which are not portable should have an earthing terminal on its metal housing.

Creepage distance shall be as far as practi- cable run in different planes. This may be achieved for instance by rounded ribs, breakings or recesses. Ribs shall have a minimum height and thickness of 3 mm. They shall be rounded with a minimum radius of 0.5 mm.

Creepage distances and clearances shall not be reduced below the minimum permissible value by influences occurring in normal operation like mechanical and magnetic forces.

IS:8945-1987

Creepage distance and clearances shall be not less than .the value’s given in Table 3. The material for parts depending upon the creepage distances are given in Table 4.

7. MARKLNG

7.1 The instrument dial shall be clearly and inde- libly marked in a.ccordance with IS : 1248 (Part l)- 1983* and IS : 8241-1976t.

7.1.1 The instrument may also be marked with the Standard Mark.

NATE - The use of the Standard Mark is governed by the provisions of the Bureau of Indian Standards Act 1986 and the Rules and Regulations made thrre- under. The Standard Mark on products covrrrd bb an Indian Standard conveys the assurance that they have, bwn producrd to comply with the r<,quirt~m(:nts of that standard under a well-dtxfined system of insprction, test- ing and quality control which is devised and sllpervisetl bv 131s and operated by the producer. Standard marked products are also continuously checked by BIS for con- formity to that standard as a further saf~~gtlartl. Details of conditions undrr which a licencc for thf. use ol‘ the Stal,dard Mark may be granted to manufacturws or producers may be obtained from the l~wcau of Indian Standards.

7.2 Measuring instruments and associated current transformers shall be marked as belonging together.

*Specification for direct acting indicating analogue electrical measuring instruments and their accessories: Part 1 General requirements ( second revision ).

tMethod of marking for identifying electrical rquip- ment for explosive atmospheres.

TABLE 3 MINIMUM VALUES OF CREEPAGE DISTANCES AND CLEARANCES

[ Clause 6.2.4.7(e) ]

INSULATION RATIN@ ~__~~_~~~~~~~_~_~

dc Voltage VoFtige

(1) (2)

24

60

110

250

440

600

660

800

1 200

1 500

3 000

24

60

125

250

440

600

750

1 000

1 500

2 000

3 000

6 000

10 000

CREEPAGE DISTANCE r---------- *---_--.-__~

n b c d

(3) (41

mm mm

6 6

6 6

6 6

6 6

6 8

10 12

14 18

20 24

28 32

36 42

50 60

90 110

12s 150

(5)

mm

6

6

8

10

12

15

22

30

40

50

72

130

180

(‘3) mm

6

6

10

12

14

20

28

36

50

70

90

160

240

(7)

6

6

6

6

6

8

10

14

20

28

3(i

60

100

5

IS I 8945 - 1987

(1)

a*

h*

TABLE 4 MATERIALS OF PARTS

[ clousa 6.2.4.7(e) 1

(2)

Ceramic materials Silicate glass Natural mica Mica Moulding compounds

Mica hloillding compounds Moulding compounds Moulding compounds bhl bnite Rubber

Moulding compounds Moulding compounds Moulding compounds Ebonite Rllhhcr Laminated paper

Laminated fabric d* Larninat-~(1 p Iper

Lrrrnlnatd fabric

*These ref(,r tu Table 3.

_- - -

Inorganic Inorganic

Organic Inorganic Inorganic I nurganic

Inorganic Organic Organic

8. TESTS

8.1 Type Tests

8.1.1 The type test is intended to prove safety against danger of explosion. It is carried out only on production samples after completion of the development of the types. Production samples in type of protection, ‘plate protection’, shall be tested in explosive mixture. Equipment in the types of protection ‘prtssurized enclosure’ and ‘e’ need only be tested in explosive mixtures, if it is considered absolutely necessary according to reie- vant Indian Standard [ see IS : 7389 ( Part 1 )- 1976* and IS : 6381-19i2t].

8.1.2 For instruments in types of protection ‘flameproof enclosure’, tests shall be carried out in accordance with IS : 2148-1981:.

8.1.3 For instruments in type of protection ‘flameproof enclosure and ‘plate protection’, tests for internal prrssure and test for flameproofness shall be carried out wlthout the instrument. The enclosuce alone ~1~~111 be tested with all parts neces- sary iur scaling including the window. If there is a chance of the interior parts causing objcction- able subdivisions then the enclosure should be tested with the instrument fitted inside or a durn- ing may replace the instrument.

8.1.3.1 The pressure test is not required ill the case of plate protection system, if the tree specific opening cross-section exceeds 80 mm’/1 capacity.

8.1.3.2 To carry out the pressure tests, rllts test pressure shall be asspecified in IS : 214%1981”.

8.1.3.3 If the enclosure (ilameproot or plate: protected ) remains unchanged after the prrssurc: test, the test shall be regarded as having been passed.

8.1.4 For instruments in type of proLectioii ‘c.‘, test for determining temperature rise shall be carried out. h or tlus, the values of’ temperatu~;: shall be decided in accordance with ‘l’able 1. ‘l‘l~s test and other teals shall be Larricd out according to IS : tJ381-1972t.

8.1.5 If the temperature rise of the short circuit strength and thus the safety 01 the insllumcrlt IS dependent 011 additional apparatus, the eircctiv<.- ness IA rhe latter shall be tested.

8.1.6 The high voltage tcbt 011 IJlt’;lSlil III,+

instrurncnts shall be cdrrled out ii1 accot ~i,rl~~c \\ 1;. 1S : 1248 ( k-art 1 ,-198X$, but at Ir,asc ;L \-oi:~lsc of :! UUU volts shall be applied even in rhe C:LX ljl’ rated voltages down up LO -10 \‘.

8.2 Routine Tests

8.2.1 These tests are intended to find out any fault in material or manufacture and to cerlly compliance with minimum requirement to stand explosion hazards.

8.2.2 For instruments in type of pwtcctlorl ‘flameproof enclosure’ and *plate protectloll’, every dimensions, such as the gap, width, Itngths or flamepath, gap between plates ill the plate stacks and thlckne>s of the plate shall be chct,ked to ensure their adherence to permissible iiruits.

8.2.2.1 The test holes shall be carefully sealed after the test is carried out. It shoulcl I,e thoroughly checked to make sure that the seal can not hark loose.

8.2.2.2 If during explosion test, IIO lgnirion takes place; during static test. no leakage: takt s

place; and if the tnclusure remains ii1laL.c; tllc,il the test may be regarded as passed.

8.2.3 l-or irlstruments ( in type ul prot(.(‘tlotl ‘e’ ), volLaye trst sllall be carried Olil ~11 .Lc ('II)-

danw lvith IS : bL81-19T2t.

8.3 In atltl~tion the illatrumerlt sllall ix, tc slc.11

accordlrlg to rclevarlt part 01 Ib : 12.t8.

6

BUREAU OF INDIAN STANDARDS

Headquarters:

Manak Bhavan, 9 Bahadur Shah Zafar Marg, NEW DELHI 119002

Telephones: 3310131, 3311375

Regional Offkes:

Central: Manak Bhavan, 9 Bahadur Shah Zafar Marg, NEW DELHI 110002

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Telearams: Manaksanstha (Common to all otfices)

Telephone

3310131, 3311375

362499

21843, 31641

412442, 412519, 412916

6329295

26348, 26349

384955, 384956

66716

53627

-

231083

63471, 69832

216876, 218292

62305

76637

25171

52435

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