Tips & News - September 2012

CRIMP BOTH ENDS

pin. The two in parallel are crimped at one end in the buttonhead and at the other in a small copper tube. The fast section has a stainless steel strain wire and parallel copper element, similar to a K link. These two are crimped at one end in the cable adapter and at the other end in a small copper tube. The two crimped copper tubes are joined by a solder connection. GENERAL STRENGTH T, K, and Slo-Fast links are designed to withstand pull forces in excess of 20 lb. This is twice the ANSI requirement of 10 lb. The actual withstand capabilities vary from fuse to fuse. Generally, larger links have greater capability, but type of construction is also a big factor. FUSE OPERATION High level faults, 1,000 amps and up, are easy to recognize. The fuse’s auxiliary tube is nearly gone or totally destroyed, and the element is consumed. When faults are in the 500 to 1,000 amp range, the auxiliary tube will burst but remain intact. In such cases most of the element is consumed depending on the size of the fuse. Unlike high-level fault incidents, lowlevel faults are sometimes hard to accept as having occurred because of the limited damage. In a low-level fault the auxiliary tube is not damaged, and the element may be nearly whole. By knowing the characteristics of a fuse link’s remains after a low-current operation, one can recognize that a fault has occurred. These characteristics vary with the fuse type.

SOLDER BOTH ENDS

CRIMP BOTH ENDS

STRAIN WIRE

COPPER ALLOY ELEMENT

STRAIN WIRE

SILVER COPPER ELEMENT

SOLDER

SMOOTH TIN ELEMENT

COPPER ELEMENT

CRIMP BOTH ENDS

CRIMP

15ampTlink

140ampTlink

Photograph1 15AmpKLink

Photograph2 140AmpKLink

T LINK LOW-LEVEL OPERATION T links, 1 through 100 amps, which have operated at low fault or overload currents, have auxiliary tubes (Photograph 4) that have not ruptured. The tin element will melt somewhere between the soldered connections. This transfers the full current to the stainless steel strain member, which in turn melts in its mid-section. After the interruption, the remaining tin element will have its original smooth surface. The element’s solder connections, and the strain member’s crimped connections will be undisturbed. In Photographs 5, 6 and 7 the auxiliary tubes did not rupture, the tin elements

140 and 200 amp T links have a heavy copper element which is soldered into the buttonhead at the top and mechanically crimped into the cable adapter at the bottom. K LINK CONSTRUCTION The 1 through 3 amp K links are constructed the same as T links. The 6 through 100 amp K links have stainless steel strain wires to provide mechanical strength and copper alloy elements to carry current. These two wires are attached in parallel by crimps at the buttonhead and cable adapter (see Photograph 1). The 140 and 200 amp K links have large silver/copper elements which, unlike T links, are crimped both at the cable adapter and buttonhead (see Photograph 2).

Photograph3

SLO-FAST LINK CONSTRUCTION

Slo-Fast links have two sections (Photograph 3). The slow section has a current-carrying heater coil wrapped around an insulated strain

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