The field of the invention relates generally to fuseholders or fuse blocks, and more specifically to modular fuse blocks adaptable for use with more than one of a plurality of overcurrent protection fuses having different current ratings and opposed, axially extending terminals of different physical size.
Fuses are overcurrent protection devices for electrical circuitry, and are widely used to protect electrical power systems and prevent damage to circuitry and associated components when specified circuit conditions occur. A fusible element or assembly is coupled between terminal elements of the fuse, and when specified current conditions occur, the fusible element or assembly melts or otherwise structurally fails and opens a current path between the fuse terminals. Line side circuitry may therefore be electrically isolated from load side circuitry through the fuse, preventing possible damage to load side circuitry from overcurrent conditions.
A variety of different types of overcurrent protection fuses are known and utilized in electrical power systems. In any given electrical power system, fuses of different electrical ratings may be utilized and various terminations options may be necessary complete electrical circuits through the fuses with connecting wires. As fuses of different ratings typically vary in a physical package size from one another, so do the fuse blocks that are used in combination with differently rated fuses. This typically results in somewhat customized fuse blocks for fuses of certain ratings and also for desired type of terminations, and a large inventory of parts is typically required to meet wide ranging needs in the field. Improvements are desired.
A considerable variety of overcurrent protection fuses are known in the art and have been used to some extent with a corresponding variety of fuseholders or fuse blocks. Conventionally, fuseholders tend to be designed to accommodate specific types and sizes of fuses only. That is, conventional fuse holders are constructed with a certain type of fuse in mind (e.g., cylindrical fuses versus rectangular bodied fuses), having certain ratings (e.g. voltage and current ratings) and certain types of terminations (e.g., ferrules versus blade contacts). Such conventional fuseholders generally lack any flexibility to accommodate other types of fuses, or other sizes of fuses.
Some known fuse holders are provided in modular form that may be assembled into larger fuse blocks, and thus may accommodate different numbers of fuses relatively easily. For example, U.S. Pat. No. 6,431,880 is commonly owned with the present application and discloses modular body sections coupled to one another, and a power bus common to all of the body sections. The fuse block of U.S. Pat. No. 6,431,880 is designed for use with ATC™ automotive blade-type fuses of Cooper Bussmann, St. Louis Mo. Such blade-type fuses include parallel terminal blades extending from a common side of a thin, rectangular, insulating housing, and a fuse element extending between the terminal blades at an interior location in the housing. The aforementioned ATC™ blade-type fuses are available with voltage ratings of 32V DC (or less) and current ratings of 1 to 40A. Typical of blade-type fuses, ATC™ fuses of different ratings are provided in the same physical package (i.e., the fuse housing and the terminal blades are typically of the same size and shape), and hence are color coded and marked so that the different ratings can easily be distinguished from one another.
For higher powered electrical systems, square or cylindrical bodied fuses are known having more substantial terminal elements extending axially from opposed ends of the fuse bodies, and also more substantial fuse elements for the increased demands of higher power applications. For example, cylindrical Class J fuses, Class R fuses, and Class H(K) fuses are available having voltage ratings of, for example 250V AC or 600V AC and current ratings of 100A, 200A, 400A or 600A. Such cylindrical fuses may include ferrules or knife blade contacts extending axially from opposing ends of the cylindrical, insulative fuse body, with a fuse element or assembly extending between the ferrules or knife blades interior to the fuse body. Ferrule type fuses are also known having current ratings of about 100A or less.
Unlike the blade-type fuses discussed above, the square or cylindrical bodied fuses of different ratings involve varying physical package size. That is the square or cylindrical bodies vary in diameter and axial length, and the associated ferrules or knife blade contacts extending from opposite ends of the fuse bodies have different proportions for differently rated fuses. Cylindrical fuses of smaller ratings typically have smaller diameter and shorter bodies relative to cylindrical fuses of larger ratings, and the ferrules and/or knife blade contacts are smaller in fuses having smaller ratings. Likewise, square bodied fuses of smaller ratings would have bodies with smaller sides relative to square bodied fuses having larger current ratings, and the knife-blade contacts would be smaller in fuses having lower current ratings.
FIG. 24 illustrates an exemplary fuseholder 100 for use with cylindrical bodied fuses having opposed, axially extending terminals. The fuseholder 100 is accordingly configured to accommodate a fuse 102 having a generally cylindrical body 104 and conductive terminal elements 106 and 108. In various embodiments, the fuse 102 may be a Class J fuse, Class R fuse, or Class H(K) fuse rated at 600V AC (or less) and having current ratings of 100A to 600A. A fuse element completes a conductive path interior to the body 100 between the conductive terminal elements 106 and 108, which may include knife blade terminal contacts as shown. The terminal elements 106 and 108 of the fuse 102 are received by terminals 110 and 112 that define fuse clips to receive the fuse terminal elements 106, 108 and also define termination structure to establish line side and load side electrical connections to electrical circuitry of an electrical power system. The line side and load side connections to the fuse holder 100 are typically established with wires using any one of a variety of techniques known in the art, such as, for example, terminal screws and/or box lug terminals accepting stripped wire ends, ring terminals, etc.
The terminals 110 and 112 of the fuseholder 100 are further provided on a nonconductive base piece 114 that may be configured for mounting to an electrical panel, chassis, or other support structure via a mounting bore 116 and a fastener (not shown). Nonconductive barrier elements 118, 120, 122 and 124 may be provided to form partial compartments for the line and load side terminals 110, 112. In the example shown, the barrier elements 118, 120, 122 and 124 extend generally perpendicular to a plane of the base piece 114 and extend only adjacent the line and load side terminal elements 110, 112, while leaving the fuse body 104 generally exposed. As such, a technician can grasp the body 104 of the fuse 102 by hand and extract it from the line and load side terminals 110, 112 without being hindered by the barrier elements 118, 120, 122 and 124.
A number of fuseholders 100 may be individually mounted side-by-side to form a multi-pole fuse block, with the barrier elements 118, 120, 122, 124 separating adjacent line and load side terminals 110, 112 in the adjacent fuse holders in the block. Some degree of protection is therefore provided against inadvertently shorting the line or load side terminals as the fuse blocks are serviced. The barrier elements 118, 120, 122, 124 also offer some protection against a risk of electrical shock via inadvertent contact by a technician's fingers, and some degree of “finger safe” operation is therefore provided. However, while the barrier elements 118, 120, 122, 124 provide some assurance against inadvertent contact with the line and load side terminals 110, 112 from the side (i.e., in a direction parallel to the plane of the base piece 114), it is still possible to contact the terminals 110, 112 from above (i.e., in a direction perpendicular to the plane of the base piece 114), whether with a user's fingers or tools.
As previously mentioned, differently rated cylindrical fuses tend to entail different physical package sizes. For example, considering class J fuses rated at 600V, a 100A fuse entails a first diameter and length of the fuse body 104, while a 200A fuse entails a second and larger diameter and length of the fuse body, as well as correspondingly larger terminal elements 106 and 108. Likewise a 400A rated fuse and a 600A rated fuse would entail increasingly larger circumferences and lengths of the cylindrical bodies 104 and still larger terminal elements 106 and 108. Large variations in size across the differently rated fuses are typical. Consequently, because of variations in the dimensions of such differently rated fuses, the fuseholder 100 is typically designed to accommodate one and only one of such differently rated fuses. In other words, differently rated fuses are not interchangeably used with the fuseholder 100, and instead a number of differently dimensioned fuseholders 100 must be produced and provided to accommodate the differently rated and differently sized fuses.
Considering the variety of fuse ratings available for cylindrical bodied fuses, and the corresponding variation in physical size, a large variety of fuseholders 100 would be necessary to provide full range of fuse blocks for use in a complex electrical power system. A rather large inventory of fuse blocks must be produced, stored and made available on site at the electrical power system, at some cost to technicians. If a fuse block of the proper size is not available, delays to full protection of an electrical system may result at even further cost. Still further, confusion can arise due to a relatively large number of available sizes of fuse blocks, leading to potential mistake in stocking and maintaining inventories, as well as installing and maintaining fuse blocks in the field.
Further compounding the issues above is the variety of termination options available for the fuseholder 100. Because the line and load side termination features tend to be integrally provided with the fuse clips, different line and load side terminals 110, 112 are necessary to provide different termination structures. In combination with dimensional differences of differently rated fuses, a large number of differently configured terminals 110, 112 may result, each of which must also be inventoried, stocked and maintained. For the exemplary fuseholder 100 depicted, ninety-one (91) total component parts have been found necessary to accommodate a set of fuses of different ratings and different termination options. Considerable cost and effort results in producing, stocking and managing such a large inventory of parts.
Still another disadvantage of the fuseholder 100 is that, when used to form larger fuse blocks having multiple poles, satisfying applicable UL specifications or IEC specifications concerning the spacing of the fuses in the blocks is difficult. For example, UL specifications (specifically UL Specification 4248) or counterpart IEC specifications may require specific positioning of the fuses in the block to achieve a minimum space or distance between energized or “live” connecting terminals in use. To satisfy such specification, a certain clearance is required between the connecting terminals such that the terminals are separated by a certain distance through air, or alternatively by another and larger distance measured on the surface of the fuseholder. The fuseholder 100 generally lacks a flexibility to meet such spacing or clearance requirements with certainty, and in some cases renders the satisfaction of such specifications difficult or impossible.
Fuseholders for square bodied fuses, such as NH fuses that those in the art would no doubt recognize, are also known and are subject to similar problems as the fuseholder 100 described above.