NOTE: Because Hubbell has a policy of continuous product improvement,we reserve the right to change design and specifications without notice.
© 2000 Hubbell • 210 N. Allen • Centralia, MO • (573) 682-5521 Printed in U.S.A.5M-RGS
Bulletin 10-7701Rev. 9/97
Applicationof
Primary Fuses
IntroductionThe wide variety of fuse links offered by the A.B.Chance Company is instrumental in reducing themany problems facing today’s coordination engineers.Besides the increasingly popular ANSI K and T fuselinks, there is available a series of precision engineeredfuse links designed especially for transformer protec-tion.
The up to date design and construction plus rigidquality control of Chance fuse links assures the co-ordination engineer of dependable electrical and me-chanical fuse link operation. In nearly all cases re-gardless of the application or coordination problemthere is a Chance fuse link to fill the need.
ScopeTo more clearly understand why Chance fuse linksare the answer to your every day fusing problems letus take a closer look at what is expected of a fuse linkas a protective device. The following discussion of fuselink application and coordination will be limited tofuse links only. However, in actual practice the utilityengineer must take into consideration substationbreakers and relay settings, reclosers, sectionalizers,
and power fuses. These devices are found on nearlyall systems and their coordination must be treated ina manner similar to that which will be discussed forfuse links.
The Fuse Link as a Protective DeviceThe fuse link may be considered as the electrical weakelement in the distribution system. This so-calledweak element is purposely introduced into the sys-tem to prevent any damage to the lines and equip-ment which make up the distribution network. When-ever an overload or fault current passes through asection of line or a piece of equipment the fuse linkwhich is the weakest element electrically must meltin time to open the circuit and prevent damage to theline or equipment. The relationship of the magnitudecurrent passing through the link to the time requiredfor the link to melt is referred to as the minimummelting time current characteristic of the fuse link,Figure 1. The relationship of the magnitude of thecurrent passing through the link to the time requiredfor the link to melt and the arc to be extinguished isreferred to as the total clearing time-current charac-teristics of the fuse link, Figure 1.
®®
POWER SYSTEMS, INC.
2
Transformer Overcurrent Protection
Consider first the fuse link as an overcurrent protec-tive device. In such an application, Figure 2, the ]inkserves to protect a piece of electrical equipment fromany damage resulting from an overcurrent. The se-lection of proper fuse links to protect equipment fromovercurrent is determined by the overcurrent capac-ity of the equipment involved. Fortunately theovercurrent capacity of electrical equipment is quiteoften expressed in a time and current relationship.The electrical equipment most commonly protectedagainst overcurrent is the distribution transformer.The time-current overcurrent capacity of distributiontransformers is given in ANSI/IEEE C 57.109 entitled“Guide For Transformer Through-Fault-Current Du-ration.” With the overcurrent time-current capacityof the equipment known, and by the use of time-cur-rent characteristic fuse link curves the proper fuselink can be chosen. The ideal fuse link should pro-vide 100% protection. In other words at any value ofovercurrent or secondary fault current up to the maxi-mum fault current available, the fuse link shouldoperate and clear the circuit before the equipment isdamaged. In actual practice however, some utilitiesmay select fuse links which permit loading of equip-ment in excess of their overcurrent capacity. Thispolicy reduces the amount of refusing necessary butalso subjects equipment to overcurrent which candamage it or shorten its life expectancy.
Short Circuit Protection
The ability to protect transformers and other electri-cal equipment from overcurrent is not all that is re-quired of a fuse link. A fuse link must act quickly toisolate equipment or lines when the equipment suf-fers internal or external failure or when the line issubjected to a fault. This requirement is necessary tolimit the outage to the smallest possible area. It isalso necessary in order to minimize damage to theequipment and lines. Limiting outages to the small-est area not only provides greater continuity of elec-trical service but also reduces the problem of locat-ing failed or damaged equipment.
Fuse links are not only applied at the transformerbut are also found in locations on the distributionsystem where only short circuit protection is required;such a situation is shown in Figure 2 where the fuselink is referred to as a sectionalizing or lateral fuse.The selection of the lateral fuse link is dictated by thefull load current and fault current at the point of itslocation and by the time-current characteristics ofthe largest fuse link in the lateral. The process ofmaking this selection is called coordination of fuselinks and will be discussed in detail under the head-ing of “Coordination of Sectionalizing Fuses.”
Figure 1
SUBSTATION
SECTIONALIZINGFUSE
TRANSFORMER
LOADOVERCURRENTFUSE
Figure 2
3
MECHANICAL APPLICATION OFFUSE LINKS IN CUTOUTSThe first step in the application of fuse links is todetermine the type of cutout in which the fuse link isto be used, and thereby establish the fuse link con-struction required. For example, most open type andenclosed type cutouts are designed to use the 20 inchminimum length “universal” type fuse links. Most 18and 23 kV cutouts and even some 15 kV cutouts re-quire fuse links longer than the 20 inch length. Openlink type cutouts require an open link type fuse linkspecifically designed for the purpose. Special cutoutsmay impose additional mechanical requirements onthe fuse links. Because of the adaptability of the fuselinks offered by the A. B. Chance Company these re-quirements can be met in nearly all cases regardlessof the cutout in use. Where problems exist on me-chanical applications not readily solved consult yourChance representative.
ELECTRICAL APPLICATION FUSE LINKSThe following factors are pertinent to the proper ap-plication of fuse links on a distribution system:
1. Safe loading characteristics of equipment to beprotected.
2. In the case of transformer fuses, the degree ofovercurrent protection to be provided.
3. Load current at the point of application.
4. The fault current available at various locationson the system.
5. Time current characteristics of fuse links to beused on the system.
6. The type of protection to be provided by the fuselink.
A typical lateral of a distribution system is shown inFigure 3. The information given in Figure 3 coversmost of the factors listed above. Providing that nosecondary fuses are used, the fuse links located atthe transformers ideally should provide overcurrentprotection, and should protect the sectionalizing fuselink. The sectionalizing fuse link will operate to iso-late the entire lateral and protect the remainder ofthe system from interruption when a primary faultoccurs between it and the transformer fuse links. Atthe cross marks on the line diagram of the lateral areindicated the fault current available at the variouslocations. The rated full load current of each singlephase transformer can be calculated by dividing theKVA of the transformer by its kV rating. If we assumeall transformers to be fully loaded the load current inthe sectionalizing fuse link will be approximately thesum of the individual transformer full load currents.
25 KVA 7.2 kVTRANSFORMER
5 KVA 7.2 kVTRANSFORMER
6 AMP K OR0.7 AMP
SLOFAST
12 AMP K OR3.5 AMP
SLOFAST
2400AMPSS.C.
80 AMP KOR
40 AMP T
SECTIONALIZINGOR PROTECTED
FUSE
2000 AMPS S.C.
6 AMP K OR14 AMP
SLOFAST
10 AMP K OR2.1 AMP
SLOFAST
15 KVA 7.2 kVTRANSFORMER
10 KVA 7.2 kVTRANSFORMER
Figure 3
Transformer Fusing
Using the information given in Figure 3, let us deter-mine the fuse link required for each transformer. As-sume the utility has standardized on the ANSI type Kfuse links for reasons of economy and supply. The 5KVA 7.2 kV transformer has a full load current ratingof approximately 0.7 amperes. Any 1 ampere fuse linkwill carry the full load current of this transformerwithout melting. However, consideration must begiven to the time current characteristics of the 1 am-pere fuse link compared with the overload capacity ofthis transformer. The ANSI overcurrent curve for thisdistribution transformer is shown in Figure 4. Also
Figure 4
ANSI/IEEE OVERCURRENTCURVE FOR A 5 KVA 7.2 KVDISTRIBUTION TRANSFORMER
6AMP
K
1AMP
K
TIM
E IN
SE
CO
ND
S
CURRENT IN AMPERES
ASA CURVE AND K TOTAL CLEARING CURVES
4
pacity of the transformer but a large portion of thiscapacity is sacrificed. Also, protection is lost againstlow overcurrents of long duration.
It can be seen from the preceding discussion that theconventional type K fuse link leaves much to be de-sired in the way of transformer protection. Let us con-sider the steps possible to provide more ideal trans-former protection where such protection is consid-ered essential. There have been for many years fuselinks available with “dual” time current characteris-tics. These fuse links have characteristics which lendthemselves to better protection and utilization of theovercurrent capacity of distribution transformers.
The A. B. Chance Company developed and markets acomplete line of dual characteristic fuse links. Thesefuse links have been so refined that their time cur-rent characteristic curves, to all practical purposes,coincide with the ANSI transformer overcurrent curve.In Figure 3, note that the alternate proper SloFastfuse links for the transformer installations are re-corded as well as the applicable type K fuse links.Figure 6 is a comparison of the total clearing timecurve of a 21 ampere SloFast fuse link with the ANSIovercurrent curve for a 15 KVA 7.2 kV transformer.The rather unusual current rating assigned to SloFastfuse links is an aid in their application since the cur-rent rating assigned is identical to the continuouscurrent rating of the transformer which they were spe-cifically designed to protect. It can be seen from Fig-ure 6 that the SloFast fuse link provides the high-est degree of transformer protection and yet allowsmaximum use of available transformer overcurrentcapacity.
Figure 5
shown is the total clearing time curve of the Chance1 ampere type K fuse link. Examination of Figure 4reveals that although protection is provided for thetransformer its full overcurrent capacity at the highvalues of current is not realized. The fusing of thistransformer with a 1 ampere type K fuse link will re-sult in the transformer being taken out of serviceunder many overcurrent conditions which would nothave damaged the transformer in any way. In orderto realize the full overcurrent capacity of the trans-former the 6 ampere type K fuse link in many in-stances would be chosen. The total clearing time curveof the 6 ampere type K fuse link is also shown inFigure 4. The application of the 6 ampere type K fuselink eliminates many unnecessary outages, but allovercurrent protection is lost. The only function thatthis fuse link can perform is to isolate the transformerfrom the system in case of faults. Many utilities jus-tify this over-fusing of transformers by the assump-tion that most secondary faults or overloads will clearthemselves before any damage to the transformer canoccur. The above assumption seems to hold truein some cases, but in others the record of burnedout transformers, does not justify this over-fus-ing practice.
The overcurrent curve of the 25 KVA transformer isshown in Figure 5. Since these larger transformersare more expensive some utilities feel that it is neces-sary to compromise between no transformer protec-tion and lOO% transformer protection. In such cases,the 12 ampere K fuse link might be selected for fus-ing the 25 KVA transformer. The use of this 12 am-pere K fuse link utilizes some of the overcurrent ca-
ANSI OVERCURRENT CURVEFOR A 25 KVA 7.2 KVTRANSFORMER
12AMP
K
20AMP
K
6AMP
K
Figure 6
ANSI OVERCURRENT CURVE FOR A15 KVA 7.2 KV TRANSFORMER
2.1 AMPSLOFAST
TIM
E IN
SE
CO
ND
S
CURRENT IN AMPERES
ANSI CURVE AND SLOFAST TOTAL CLEARING CURVE
TIM
E IN
SE
CO
ND
S
CURRENT IN AMPERES
ANSI CURVE AND K TOTAL CLEARING CURVES
5
The dual element SloFast Fuse Link has two distinctsections to assure overall protection.
Coordination of Sectionalizing Fuses
In selecting a fuse link for use at a sectionalizing point,we must give consideration to coordination, that isthe cooperation of one fuse link with another to limitoutages to the smallest possible section of the distri-bution system.
When coordination is being considered, thesectionalizing fuse link shown in Figure 3 is referredto as the “protected” fuse, whereas the fuse links lo-cated at the transformers are referred to as “protect-ing” fuses. These two terms, “protected” and “pro-tecting” are used to indicate that one fuse link, theprotecting, operates and clears the circuit before theother, the protected, is damaged. In order to providethe necessary coordination between these fuse linkswe must refer to the fuse link time current charac-teristic curves. Using these curves, we first determinethe maximum total time required by the protectingfuse link to clear the maximum short circuit faultcurrent which is available at the point of its applica-tion. The proper protected fuse must carry the fullload current and have a minimum melting time greaterthan the maximum total clearing time of the protect-ing fuse at the maximum fault current available atthe protecting fuse. To provide protection againstoperating variables, 75% of the minimum melting timeof the protected fuse link is often used. Naturally, indetermining the coordination of the sectionalizing fuselink with transformer fuse links the largest trans-former fuse link in the section should be consideredsince it will place the strictest coordination require-ments on the sectionalizing fuse link.
In Figure 3 it is necessary to determine thesectionalizing fuse link required to coordinate withthe largest fuse link in the branch which in this caseis the 3.5 ampere SloFast fuse link used to protectthe 25 KVA transformer. The total clearing time curveof the 3.5 ampere SloFast fuse link indicates that themaximum time required by this fuse link to clear a2400 ampere fault is .0134 seconds. The propersectionalizing fuse link, therefore, must be capableof carrying 2400 amperes for .0134 seconds withoutbeing damaged. The ANSI type T fuse links have beenselected for our sectionalizing fuse because of theirslow time current characteristics. The minimum melt-ing time curves of the type T fuse links indicate thatthe minimum melting time of a 40 ampere T link at2400 amperes is .0185 Sec. As previously stated, toallow for operating variables, 75% of this minimummelting time is used, or .0139 seconds. The 40 am-
SUBSTATION
14 AMPSLOFAST
100 KVA 7.2 KVTRANSFORMER
40 AMP TPROTECTING
FUSE
2400 AMPS. S.C
3.5 AMPSLOFAST
25 KVA 7.2 KVTRANSFORMER
80 AMP TPROTECTED
FUSE
Figure 7
pere T fuse link will, therefore, meet the necessarycoordination requirements.
Where two sectionalizing fuses are in series the onefarthest from the power source becomes the protect-ing link and the one nearest the power source be-comes the protected link. In this application the properprotected link has to be selected in the same manneras in the application where a transformer fuse pro-tects a sectionalizing fuse. As an example, there aretwo sectionalizing fuses shown in series in Figure 7.In the consideration to select the proper fuse link forthe point nearest the power source this fuse link be-comes the protected link. It has already been deter-mined that a 40 ampere type T link is required forwhat has now become the protecting link. By refer-ence to the time current characteristic curves andthe use of the 75% operating variable factor it can bedetermined that the protected link should be an 80ampere type T.
Use of Time Current Characteristic Curves
and Coordination Tables
Since time current characteristic curves are usuallyprinted on transparent paper, it is possible to overlaythe total clearing time characteristic curve with theminimum melting time characteristic curve or viceversa. The minimum melting curve can be shifteddownward by 25% with respect to the total clearingtime curve. This shift, since the curves are printed onlog-log paper, automatically provides for 75% of the
Heat absorberHeater coil Fuse wire
Strain wire
Solder junction
Insulated strain pinFast
sectionSlow section
6
minimum melting time to be used in coordination.With the time current characteristic curves so ar-ranged we can readily determine the values of cur-rent at which any two fuse links will coordinate.
To simplify the process of coordination the A. B.Chance Company also provides coordination chartsfor all fuse links which they manufacture. In the caseof the SloFast fuse links, coordination charts are pro-vided with the SloFast link as the protecting fuse linkand all other Chance fuse links as the protected fuselinks. These charts are used to determine the properprotected fuse link when the short circuit currentavailable and the size of the protecting fuse link areknown.
The use of coordination charts can be illustrated inFigure 7 by determining the proper fuse link to belocated nearest the substation. In order to use thecharts, we must first determine which fuse link isthe protecting fuse link and which fuse link is theprotected fuse link. The protected fuse link is alwaysthe fuse link which is located nearest the power sourceand the protecting fuse link is that fuse link locatedadjacent to the protected fuse link and nearest theload. Refer to the coordination chart of the type Tfuse link. If a 40 ampere Type T fuse link is the pro-tecting fuse link and the available short circuit cur-rent is 2400 amperes, this chart indicates that theprotected link must be an 80 ampere T. The 80 am-pere T link will coordinate with a 40 ampere T link atshort circuit currents up to 3700 amperes.
“Rule of Thumb” Method for Coordination
of ANSI Type K or Type T Fuse Links
Another method of coordinating fuse links is possiblewhen the ANSI K or T fuse links are used. This isreferred to as the “Rule of Thumb” method. The “Ruleof Thumb” method is stated as follows:
Satisfactory coordination between adjacentratings of preferred or adjacent ratings ofnon-preferred fuse links is provided up tocurrent values of 13 times the smaller orprotecting fuse link rating for Type K fuselinks and 24 times the smaller or protect-ing fuse link rating for Type T fuse links.
The above coordination factors are made possible bythe standardization of maximum allowable arcing timeapplied to the fuse links. The 75% of minimum melt-ing time factor is also taken into consideration by thisrule of thumb method. Obviously, when ANSI fuselinks are used, the rule of thumb method simplifiesthe process of coordination in some instances.
Referring again to Figure 7, this method can be usedin checking the fuse link required adjacent to thesubstation . In using the rule of thumb method, wemust again use the terms “protected” and “protect-ing” fuse links. The method states that satisfactory
coordination between adjacent preferred or adjacentnon-preferred ratings of type “T” fuse links is pos-sible if the short circuit current does not exceedtwenty-four times the rating of the protecting fuselink, or in this case our 40 ampere “T” fuse link. It isevident that if the short circuit current does not ex-ceed 960 amperes (24 x 40 + 960) we could use a 65ampere T fuse link at the substation. However, theactual current is 2400 amperes and the rule of thumbmethod only establishes that a “T” fuse link largerthan the 65 ampere rating is required. Either of thetwo previous described methods (time current curvesor coordination charts) can be used to determine thislarger required “T” fuse link.
MECHANICAL INTERCHANGEABILITYIn addition to electrical characteristics, a fuse linkmust have certain physical and mechanical featuresin order for it to be interchangeable. Mechanical in-terchangeability is equally as important as electricalinterchangeability. Besides the standard universalfuse link for open and enclosed type cutouts, thereare a few special fuse links for use in what might becalled non-conventional or non-universal type cut-outs.
7
TABLE 1COORDINATION CHART
forCHANCE TYPE “K” (FAST) ANSI FUSE LINKS
6
14510060
8
220185150
10
295295295
170
12
370370370
320190
15
490490490
490400250
20
620620620
620620480
310
25
840840840
840840840
700440
30
100010001000
100010001000
1000750480
40
130013001300
130013001300
130013001000
600
50
160016001600
160016001600
160016001600
1175740
65
225022502250
225022502250
225022502250
225018401150
80
265026502650
265026502650
265026502650
265026501950
1250
100
345034503450
345034503450
345034503450
345034503450
26501500
140
580058005800
580058005800
580058005800
580058005800
580058004800
3000
200
940094009400
940094009400
940094009400
940094009400
940094009400
94004500
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type “K” Fuse Link Ampere Rating
TABLE 2COORDINATION CHART
forCHANCE TYPE “T” (SLOW) ANSI FUSE LINKS
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.
6
280280280
8
390390390
10
510510510
340
12
690690690
690400
15
920920920
920850480
20
115011501150
11501150990
550
25
150015001500
150015001500
1190670
30
190019001900
190019001900
19001500890
40
249024902490
249024902490
249024902000
1100
50
300030003000
300030003000
300030003000
22501250
65
390039003900
390039003900
390039003900
390030001700
80
480048004800
480048004800
480048004800
480048003700
2100
100
620062006200
620062006200
620062006200
620062006200
50002700
140
950095009500
950095009500
950095009500
950095009500
950095006600
3900
200
150001500015000
150001500015000
150001500015000
150001500015000
150001500015000
150005200
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type “T” Fuse Link Ampere Rating
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.
Protecting Type“K” Fuse LinkAmpere Rating
123
68
10
121520
253040
506580
100140200
Protecting Type“T” Fuse LinkAmpere Rating
123
68
10
121520
253040
506580
100140200
8
TABLE 3COORDINATION CHART
forCHANCE “MS” FUSE LINKS
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type “MS” Fuse Link Ampere Rating
TABLE 4COORDINATION CHART
forCHANCE TYPE SLOFAST FUSE LINKS
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.
5 7
640
10
980980
15
13001300850
20
163016301600
780
25
210021002100
16501000
30
260026002600
260019001200
40
325032503250
325032502250
1400
50
420042004200
420042004000
30002150
65
530053005300
530053005300
530039002800
80
620062006200
620062006200
620062004900
3200
100
840084008400
840084008400
840084008400
62001400
125
100001000010000
100001000010000
100001000010000
1000073001700
150
100001000010000
100001000010000
100001000010000
10000100009700
6700
200
100001000010000
100001000010000
100001000010000
100001000010000
10000100008200
3Protecting Type“MS” Fuse LinkAmpere Rating
357
101520
253040
506580
100125150
200
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type SloFast Fuse Link Ampere Rating
.2 .3
35
.4
52
.6
62
.7
65
1.0
1128775
6760
1.3
135112100
9590
1.4
143120110
104100
1.6
175160150
14514090
2.1
230225215
211208168
145130
3.1
325325325
325325295
275265230
3.5
340340340
340340315
300285250
4.2
440440440
440440440
415405380
310
5.2
530530530
530530530
530530500
445330300
6.3
620620620
620620620
620620620
570450430
300
7.0
660660660
660660660
660660660
610510480
350
7.8
820820820
820820820
820820820
820740700
610480
10.4
106010601060
106010601060
106010601060
106010501025
940820690
650
Protecting TypeSloFast Fuse Link
Ampere Rating
.2
.3
.4
.6
.71.0
1.31.41.6
2.13.13.5
4.25.26.3
7.07.8
10.4
9
TABLE 5COORDINATION CHART
forCHANCE TYPE SLOFAST AND TYPE “K” (FAST) ANSI FUSE LINKS
TABLE 6COORDINATION CHART
forCHANCE TYPE SLOFAST AND TYPE “T” (SLOW) ANSI FUSE LINKS
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type “K” Ampere Rating
6
165140125
8
220210195
190190
10
295295295
285285240
12
370370370
370370350
320320
15
490490490
490490490
490490440
20
620620620
620620620
620620620
550
25
840840840
840840840
840840840
840700700
30
100010001000
100010001000
100010001000
1000950950
820
40
130013001300
130013001300
130013001300
130013001300
12301100
50
160016001600
160016001600
160016001600
160016001600
160015501400
1400
65
225022502250
225022502250
225022502250
225022502250
225022502250
225020001700
80
265026502650
265026502650
265026502650
265026502650
265026502650
265025502300
100
345034503450
345034503450
345034503450
345034503450
345034503450
345034503250
140
580058005800
580058005800
580058005800
580058005800
580058005800
580058005800
200
940094009400
940094009400
940094009400
940094009400
940094009400
940094009400
Protecting TypeSloFast Fuse Link
Ampere Rating
.2
.3
.4
.6
.71.0
1.31.41.6
2.13.13.5
4.25.26.3
7.07.8
10.4
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type “T” Fuse Link Ampere Rating
6
285285285
275275
8
385385385
385385370
10
510510510
510510510
510510
12
690690690
690690690
690690690
15
920920920
920920920
920920920
920
20
115011501150
115011501150
115011501150
115011501150
25
150015001500
150015001500
150015001500
150015001500
1500
30
190019001900
190019001900
190019001900
190019001900
190019001800
1800
40
249024902490
249024902490
249024902490
249024902490
249024902490
24902300
50
300030003000
300030003000
300030003000
300030003000
300030003000
300030002800
65
390039003900
390039003900
390039003900
390039003900
390039003900
390039003900
80
480048004800
480048004800
480048004800
480048004800
480048004800
480048004800
100
620062006200
620062006200
620062006200
620062006200
620062006200
620062006200
140
950095009500
950095009500
950095009500
950095009500
950095009500
950095009500
200
150001500015000
150001500015000
150001500015000
150001500015000
150001500015000
150001500015000
3
83
3
78
Protecting TypeSloFast Fuse Link
Ampere Rating
.2
.3
.4
.6
.71.0
1.31.41.6
2.13.13.5
4.25.26.3
7.07.8
10.4
10
TABLE 8ELECTRICAL AND MECHANICAL INTERCHANGEABILITY TABLE
forEQUIVALENT FUSE LINKS
TABLE 7COORDINATION CHART
forCHANCE TYPE SLOFAST AND TYPE “MS” FUSE LINKS
Catalog Number
M3MSAM5MSAM7MSAM10MSAM15MSA
M20MSAM25MSAM30MSAM40MSAM50MSA
M65MSAM80MSAM100MSAM125MSAM150MSAM200MSA
Chance Type MSA Fuse Links
Catalog Number
21003 & 21003-U21005 & 21005-U21007 & 21007-U21010 & 21010-U21015 & 21015-U
21020 & 21020-U21025 & 21025-U21030 & 21030-U21040 & 21040-U21050 & 21050-U
21065 & 21065-U21080 & 21080-U21100 & 21100-U21125 & 21125-U21150 & 21150-U21200 & 21200-U
Ampere Rating
357
1015
2025304050
6580
100125150200
Kearney Type KS and KS-U Fuse Links
Ampere Rating
357
1015
2025304050
6580
100125150200
Maximum Currents (R.M.S. Amperes) For Safe Co-ordination
Protected Type “MS” Fuse Link Ampere Rating
5
410410410
410410400
7
650650650
650650650
650650650
10
980980980
980980980
980980980
980
15
130013001300
130013001300
130013001300
130013001300
20
163016301630
163016301630
163016301630
163016301630
16301500
25
210021002100
210021002100
210021002100
210021002100
21002100
30
260026002600
260026002600
260026002600
260026002600
260026002600
2600
40
325032503250
325032503250
325032503250
325032503250
325032503250
325032503000
50
420042004200
420042004200
420042004200
420042004200
420042004200
420042004200
65
530053005300
530053005300
530053005300
530053005300
530053005300
530053005300
80
620062006200
620062006200
620062006200
620062006200
620062006200
620062006200
100
840084008400
840084008400
840084008400
840084008400
840084008400
840084008400
125
100001000010000
100001000010000
100001000010000
100001000010000
100001000010000
100001000010000
150
100001000010000
100001000010000
100001000010000
100001000010000
100001000010000
100001000010000
200
100001000010000
100001000010000
100001000010000
100001000010000
100001000010000
100001000010000
3
300300300
300300
Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time ofthe protected link.
Protecting TypeSloFast Fuse Link
Ampere Rating
.2
.3
.4
.6
.71.0
1.31.41.6
2.13.13.5
4.25.26.3
7.07.8
10.4
11
CONVERSION TO ANSI FUSE LINKS
buttonhead, removable buttonhead and/or open link styles— that you would use on your system.
Construction details such as construction of the fuse ele-ment, auxiliary tubes and fuse link cable size and coatingshould also be considered along with the quality and per-formance of the fuse links produced.
In Chance type “K” fuse links, elements are made of silvercopper or silver alloy and Type “T” fuse links are made witha tin fuse element.
The purpose of the auxiliary tube is to assist the cutout inthe clearing of low fault currents and to protect the fuseelement from physical damage.
Converting to EEE-NEMA LinksAfter the type of link, “K” or “T” is selected, the followingsteps are suggested as a guide to implementing a conver-sion program.
1. Select the supplier — Considerations in determiningwhich manufacturer or manufacturers from whom youwould purchase fuse links include availability of stocks,reputation of company service rendered by salesman, and,of course, the quality and consistency of performance ofthe fuse links produced.
Samples of links should be obtained from all potential sup-pliers and should include all physical types — solid
Advantages of ConversionThrough the joint efforts of users and manufacturers, the ANSI Standards for Distribution Fuse Links were established toprovide the levels of performance and utility necessary to meet modern protective practices and operating conditions.They serve the two-fold purpose of providing guidance to the manufacturer and assurance to the user that specificelectrical requirements are met.
These joint standards, along with existing ANSI standards, set forth characteristics that will allow and provide for theelectrical, as well as mechanical, interchangeability of fuse links. Conversion to ANSI standard fuse links therefore per-mits multiple sources of supply for fuse links.
The ANSI standards are prepared so as to still permit the utility engineer to select fuse links using his individual judgmentbased on the details of manufacture, use with related equipment and other application factors.
Two Speed Ratios AvailableThe joint ANSI standards have established two types of fuse links, designated Type “K” and Type “T”. The Type “K” linkcommonly called “fast” has speed ratios of the melting time-current characteristics varying from 6 for the 6-ampere ratingto 8.1 for the 200 ampere rating. Type “T” (slow) fuse links have speed ratios of the melting time-current characteristicvarying from 10 for the 6-ampere rating to 13 for the 200 ampere rating.
The type of link selected, “K” or “T”, is based largely on the time-current characteristics of the fuse link presently used, ifsuch characteristics meet present day coordination requirements. The more closely the time-current characteristics meetthose of the present fuse links, the easier the conversion.
TIM
E IN
SE
CO
ND
S
“Representative” minimum and maximum curvesfor ANSI Type “T” (slow) fuse links.
“Representative” minimum and maximum timecurrent characteristic curves for ANSI Type “K”(fast) fuse links.
CURRENT IN AMPERES CURRENT IN AMPERES
TIM
E IN
SE
CO
ND
S
12
Type K Fuse Link
For OverloadProtection of
Transformers*
Ampere Rating
“K” or “T”
368
1015202530
40506580
100
100 or 140140
140 or 200
“K”
101220
25 or 3040506580
80 or 100100 or 140
140140 or 200140 or 200
200——
“T”
68
10 or 12
1520 or 2525 or 3030 or 40
40
5065 or 8080 or 100
100100 or 140
140200—
For Short CircuitProtection**
Ampere Rating
Figure 6
TABULATION OFMINIMUM MELTING CURRENT VALUES
TYPE K 10 AMP FUSE LINKManufacturer
Time Periodin Seconds
300100101.1
CHANCE
19.520.025.042.5
129.0
A
19.520.023.043.0
130.0
C
20.021.026.045.0
130.0
B
19.520.024.543.0
129.0
Current in Amperes
TABULATION OFMINIMUM CLEARING VALUES
TYPE K 10 AMP FUSE LINK
Time Periodin Seconds
300100101.1
CHANCE
23.524.029.552.0
167.0
A
23.023.527.049.0
170.0
C
23.025.031.054.0
180.0
B
23.024.029.054.0
170.0
Manufacturer
Current in Amperes
CHANCE TYPE MS ANDMSA FUSE LINKS
Ampere Rating
357
1015202530
40506580
100
125150200
RECOMMENDED CHANCE ANSIFUSE LINK
3. Make-up cross reference charts — Using either thecomposite curves or the tabulations used to develop thesecomposite curves, a cross reference chart like the one shownbelow should be made comparing the ANSI link and thelink now in use. (See Fig. 8 for typical example.)
4. Check coordination with other overcurrent protec-tion equipment — In some instances it may be necessaryto check the coordination of the ANSI link with otherovercurrent protection devices, but this should not be aserious problem unless the time-current characteristics ofthe selected ANSI link has a considerably different speedratio than the fuse link now in use.
5. Change records and drawings — With the cross refer-ence charts you can change over all records and drawingsto specify the proper size ANSI links.
You are now ready to put these new links on your system.There are several methods by which this has been done.One of the following examples may be found to have par-ticular advantages to your company.
Convert one division at a time, using salvaged links inun-converted districts.
Convert all but one division, using all the salvagedfuse links in one un-converted division until they aredown to a disposable level.
Convert all divisions simultaneously, scrapped all non-ANSI links in stock.
Many factors will affect the conversion finally adopted. Thesefactors can best be evaluated by the utility involved.
The weather resistance of these auxiliary tubes should beevaluated since any fuse link may be in service many yearsbefore it operates.
The type of coating used on the fuse link cable should pre-vent excessive corrosion which could result in cable break-age. Chance engineers have found that lead coating givesexcellent resistance to corrosion.
It is imperative that every link used on your system consis-tently match the published time-current characteristiccurves so as to properly coordinate the protective equip-ment.
2. Make-up composite time current characteristicscurves — In order to meet specified electrical interchange-ability requirements, all manufacturers’ fuse links are re-quired to meet minimum and maximum melting currentvalue at three time points (a) 300 seconds for fuse linksrated 100 amps and below and 600 seconds for fuse linksrated 140 and 200 amps, (b) 10 seconds and (c) 0.1 sec-onds. These standards for minimum, and maximum melt-ing time result in a band curve for each rating of each type(see Fig. 1 and 2 on page 2).
Because these ANSI standards allow a band width for theminimum and maximum melting time curves and a vari-ance in factors applied for arcing time by different manu-facturers, each manufacturer’s curve varies slightly al-though still within the limits of the standards. It is there-fore recommended that on each size of link a compositeminimum melting curve and a composite total clearing timecurve be constructed from the individual curves on eachmake of link to be used. This can be done by preparing achart for each size link as shown below.
To actually prepare the composite curve for each size link,the minimum figure at each current rating should be se-lected and plotted for the minimum melting composite curve.
When plotting the total clearing time curve, the maximumfigure should be selected at each current rating.
The composite curves thus obtained will provide a bandwithin which the fuse links of all the selected suppliers willoperate.
Type T Fuse Link