Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
  • H01H85/02—Details
  • H01H85/04—Fuses, i.e. expendable parts of the protective device, e.g. cartridges
  • H01H85/041—Fuses, i.e. expendable parts of the protective device, e.g. cartridges characterised by the type
  • H01H85/048—Fuse resistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
  • H01H85/0013—Means for preventing damage, e.g. by ambient influences to the fuse
  • H01H85/0021—Means for preventing damage, e.g. by ambient influences to the fuse water or dustproof devices
  • H01H2085/0034—Means for preventing damage, e.g. by ambient influences to the fuse water or dustproof devices with molded casings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
  • H01H85/0013—Means for preventing damage, e.g. by ambient influences to the fuse
  • H01H85/0021—Means for preventing damage, e.g. by ambient influences to the fuse water or dustproof devices
  • H01H85/003—Means for preventing damage, e.g. by ambient influences to the fuse water or dustproof devices casings for the fusible element

Definitions

• This invention has its most important, but not only, application to the field of fuses designed to protect phone lines against surges caused primarily by lightning.
• Lighting striking phones lines is a common problem. Lightning strikes can cause current surges to be induced into circuits in telephone lines which can damage switching station and other equipment. The same is true under conditions referred to as power cross. Power cross occurs when a power line comes into physical and electrical contact with a telephone line which can also damage equipment from a power surge created in the telephone line. To minimize damage from such conditions, elements referred to as wire-wound resistors are placed in the line to absorb some of the energy of a power surge caused by these conditions.
• the surge resistor fuse is constructed of two major components: a wire-wound resistor and a thermal fuse. The wire-wound resistor will melt to open the circuit under some unduly severe energy surge conditions.
• the thermal fuse protects the circuit under more modest overload conditions caused by short circuit or prolonged overloads.
• the use of a separate resistor and a thermal fuse requires greater space than if such elements were combined in a single housing, and the purchase of two separate elements which is more expensive than if both elements shared a common enclosure.
• a broad aspect of the present invention comprises a resistor and fuse as described which share a common housing and connecting leads.
• the invention includes the placement of the fuse element inside the body of the resistor. This makes the fuse much more compact and maximizes the desired heat transferring function of the resistor.
• the surge resistor fuse of the present invention comprises a hollow insulating tube around which resistance wire is spirally wound or otherwise deposited, and the fuse element is a section of fuse wire forming a finger of solder extending axially inside the tube.
• the finger of solder occupies only a part of the volume of the insulating tube interior so that when the solder melts, it can quickly flow into the remaining space inside the tube to form a gap or discontinuity in the circuit involved.
• Figure 1 is a perspective view of the surge resistor fuse of the present invention.
• Figure 2 is a cross-sectional view of the surge resistor fuse of the present invention.
• Figure 3 is an enlarged view of the connection between the solder finger and the first lead wire.
• Figure 4 is a further enlarged view of Figure 3 showing the details of the coating of the solder finger and first lead wire.
• the surge resistor fuse of the invention illustrated in Figure 1 and indicated by reference numeral 2 includes an outer generally cylindrically- shaped enclosure 4 from which extends a pair of connecting leads 6-6'. The leads are shown extending from one end of the enclosure.
• the enclosure 4 is shown closely enveloping the resistor and fuse element to be described to preferably be arranged in a manner which makes a product of minimum overall size without adversely affecting the desired functions of these two elements.
• the enclosure 4 has a layer of insulating material which could be molded over the resistor portions of the fuse to be described, or more preferably, by dipping the resistor and fuse element in a body of the desired material to form a coating thereover which seals the interior from the external elements.
• the resistor comprises a hollow insulating tube 12, preferably made from a ceramic material which is well-known in the art.
• the size of the tube will vary with the capacity of the resistor.
• the tube 12 has a first end 14 and a second end 16.
• a first conductive end cap 18 preferably made of silver-plated stainless steel.
• the first end cap 18 encloses the first end 14 of the tube 12, and is anchored to the tube 12 by an interference press-fit.
• Attached to the inner center of the first end cap 18 and extending axially through the tube 12 is a solder finger 20.
• the solder finger 20 is soldered to the inside of the first end cap 18 at 9 ( Figure 2) as by heating the first end cap.
• a second end cap 22 At the second end 16 of the tube 12 is a second end cap 22.
• the second end cap 22 has an opening 24 in the center.
• the second end cap 22, which is preferably made of stainless steel, is attached to the tube 12 by an interference press-fit.
• a resistance wire 26 having the resistor referred to.
• the diameter of the wire 26 will vary depending on the value and surge capacity desired. The distance between turns of the wire 26 should be maximized for best performance.
• the ends of the resistor wire 26 are welded to the first end cap 18 and the second end cap 22, respectively.
• the surge capacity of the wire 26 depends in part on the cross-sectional area of the wire. The wire 26 acts to absorb energy from the current pulse created by any power surge.
• the fuse wire may be a finger of solder 20 coated, if necessary, with a material which prevents oxidation of the solder. This coating is shown in Figure 4 where it is identified by reference numeral 21. It may be made of a material commonly referred to as a "hot melt adhesive.”
• the finger of solder 20 is soldered to the inside of the first end cap 18 at 9 ( Figure 2) as by heating the end cap to melt the end of the solder finger 20.
• the solder finger forms an extension of the straight inner end portion 6a 7 of the lead 6'.
• the lead 6' bends sharply around the end face of the tube 12 so that the end cap 18 is locked upon the end 14 of the tube 12.
• the lead then extends axially through the end cap opening 24.
• the other lead 6 is a straight lead welded to the outer face of end cap 22.
• the following specifications are applicable to a resistor and fuse element like that shown in the drawings designed to have a cold resistance value of 82.5 ohms: (1)
• the fuse opens under the following conditions: (a) a prolonged overload of 350 ma. flowing for a maximum of 3 minutes to deliver 10 watts of power to the resistor; (b) a prolonged overload of 780 ma. flowing for a maximum of 30 seconds to deliver 50 watts of power to the resistor.
• Lead specifications external lead spacing - .200"; lead diameter - .020";
• Resistor specifications diameter - .0035"; resistor wire material - Stablohm 800 (75% nickel, 20% chromium and balance is aluminum and copper) ; wire resistors - 65.30 ohms/ft. winding spacing - .0035" number of turns - 20.5
• Insulating tube specifications tube material - Steatite L3 tube outer diameter - .235" tube inner diameter - .05" tube length -.370"
• the surge resistor fuse acts as follows. Under the conditions of 1(a) and 1(b), the resistor wire 26 heats and the solder finger 20 melts, thus opening the fuse. Under the conditions of (2) , the wire 26 around the tube 12 melts and opens like a fast- acting fuse, thus opening the circuit. Finally, under the conditions listed in (3) , the resistance wire 26 limits current through the surge resistor fuse, thus allowing the solder finger 20 to remain intact.

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• Fuses (AREA)
• Emergency Protection Circuit Devices (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

Family

ID=22529707

Family Applications (1)

Country Status (4)

Families Citing this family (12)

Family Cites Families (7)

• 1993
  • 1993-11-09 US US08/149,312 patent/US5418516A/en not_active Expired - Fee Related
• 1994
  • 1994-03-25 TW TW083102632A patent/TW282550B/zh active
  • 1994-11-08 AU AU81334/94A patent/AU8133494A/en not_active Abandoned
  • 1994-11-08 WO PCT/US1994/012851 patent/WO1995013622A2/en not_active Ceased

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