US3255329A - Fuse adapter - Google Patents

Description

June 7, 1966 A. R. NORDEN FUSE ADAPTER Filed May 28, 1963 f s. M M

N an m W 1 E W mm ATTORNEYS United States Patent 3,255,329 FUSE ADAPTER Alexander R. Norden, New York, N.Y., assignor to Murray Manufacturing Corporation, Brooklyn, N.Y., a corporation of New York Filed Mar..28, 1963, Ser. No. 268,725 2 Claims. (Cl. 200-119) This invention relates generally to fuse adapters for receiving type S fuses. The invention is characterized by a novel spacing member which eliminates all possibility of connecting into an electrical circuit a fuse of higher rating than the electrical circuit may safely carry. The invention is useful in any type S fuse adapter, but it is particularly useful in the type S fuse adapters described incopending patent application Serial No. 291,771, which was filed on July 1, 1963 for a Fuse Mounting Assembly.

Type S fuses are designed to minimize the possibility of connecting into an electrical circuit a fuse of higher rating; e.g. connecting a 30 amp. fuse into a 20 amp. circuit, thereby allowing the circuit to become substantially overloaded without blowing the fuse. This is done by using different screw threads on different type S fuse sizes and by using different dimensions for the line contact of the fuse. Under ordinary conditions, the different screw threads and different contact dimensions are adequate to' prevent the fuse from making contact if it is inserted in the wrong size fuse holder. In some cases, however, it is possible for the fuse to make contact in the wrong size fuse holder notwithstanding the difference in screw threads and contact dimensions.

Accordingly, the principal object of this invention is to provide a fuse adapter which eliminates all possibility of connecting into an electrical circuit a fuse of higher rating than the electrical circuit.

Other objects and advantages of the invention will become apparent to those skilled in the art from the following description of one specific embodiment of the invention, as illustrated in the attached drawings, in which:

FIGURE 1 is an elevation view of a first type S fuse; FIGURE 2 is an elevation view of a second type S fuse;

FIGURE 3 is a plan view of a fuse holder with a type S fuse adapter inserted therein;

FIGURE 4 is an elevation section taken on the line 4-4 of FIGURE 3;

FIGURE 5 is a perspective view of'a portion of the fuse holder shown in FIGURES 3 and 4;

FIGURE 6 is an elevation section of one illustrative embodiment of this invention; and

FIGURE 7 is an elevation section of a fuse holder with the fuse adapter of FIGURE 6 inserted therein.

FIGURE 1 shows a prior art type S fuse, which comprises a ceramic body member 10 on which are formed rectangular screw threads having an accurately determined pitch and width. The ceramic body 10 is enlarged at the top to form a shoulder 12, which supports a metallic load spring contact 14. The ceramic body 10 is hollow, and the spring load contact 14 is coupled to the inside of body member 10 through a slot formed therein. A fuse element is connected within the hollow portion of body 10 between the load contact 14 and a line contact 16, which is attached to the bottom of body 10. The top of the body 10 is closed by a metallic cap 18, which contains a mica window to permit visual inspection of the fuse element.

The fuse shown in FIGURE 1 is a amp. fuse. FIG- URE 2 shows a amp. type S fuse, which differs from the 20 amp. fuse only in the length of the line contacts 16 and 16'. This difference of length, however, is critical because it ordinarily prevents a 30 amp. fuse from mak- 3,255,329 Patented June 7, 1966 ing contact in a fuse holder which is designed to receive a 20 amp. fuse. In a 20 amp. fuse holder, the thread dimensionsare selected so that the line contact of the 30 amp. fuse will not touch the line contact of the fuse holder when the 30 amp. fuse is fully screwed into the socket. The 20 amp. fuse, however, will make contact in the 20 amp. fuse socket because of its longer line contact. This can be better appreciated by referring to FIGURES 3 and 4, which show a fuse holder with a type S fuse adapter inserted therein. (This particular fuse holder and fuse adapter are disclosed and claimed in the above-noted copending patent application.)

Referring to FIGURES 3 and 4, the holder comprises a block 20 of insulating material in which is formed a generally cylindrical recess 22. A metallic line contact 24 is located in the bottom of the recess (FIGURE 4), and a metallic load contact 26 is located in one side of the recess. Two rectangular slots (FIGURE 3!) are formed in the sides of recess 22 to receive a fuse adapter, which can be a type S fuse adapter or an Edison type fuse adapter, as explained fore fully in the abovenoted copending US. patent application. In this particular example, a type S fuse adapter is shown inserted in the recess of the fuse holder.

The type S fuse adapter comprises a hollow shell member 28 which is made of insulating material and threaded on the inside to receive a type S fuse. Shell member 28 is secured on the top to a metallic clip 30, which is disclosed more fully in FIGURE 5. Clip 30 has two downwardly projecting legs 32 and 34 each of which is provided with a corresponding lanced hook member 36 and 38. When the fuse adapter is inserted into the fuse holder recess, hook members 36 and 38 engage in matching notches 36' and 38' (FIGURE 4)-to secure the fuse adapter in the recess. It should be noted that notch 36 is formed in load contact 26, which means that clip 30 acts as an extension of load contact 26. When a 20 amp. fuse (FIGURE 1) is screwed into shell member 28, the load contact 14 of the fuse bears against the top of clip 30, thereby connecting fuse load contact 14 to holder load contact 26. The line contact 16 of the 20 amp. fuse makes contact directly with the line contact 24 of the holder via an opening formed in the bottom of shell member 28.

When a 30 amp. type S fuse (FIGURE 2) is screwed into a 20 amp. fuse adapter, however, as indicated by the dashed lines in FIGURE 4, the line contact 16 of the fuse does not normally touch fuse holder line contact 24 because of the difference of length between contacts 16 (FIGURE 1) and 16' (FIGURE 2). Under normal conditions, this prevents the 30 amp. fuse from being connected into a 20 amp. circuit. It should be noted, however, that there is a small gap G (FIGURE 4) between the bottom of the fuse adapter and the fuse holder recess. This gap is necessary to insure that lanced hooks 36 and 38 will snap into their corresponding notches 36' and 38' when the fuse adapter is inserted into the fuse holder recess. But if the gap G is larger than the difference of length between the line contact 16 of the 20 amp. fuse and the line contact 16' of the 30 amp. fuse, the 30 amp. fuse will make contact in the 20 amp. socket inspite of the difference of length in the line contacts 16 and 16'. Furthermore, since the difference of length is quite small, the likelihood that this abnormal condition will occur is reasonably high.

In accordance with this invention, there is provided means to insure that the 30 amp. fuse cannot make contact in a 20 amp. socket when the gap G is larger than the difference of length between theline contacts of the two fuses. This can be better appreciated from an examination of FIGURES 6 and 7, which show one illustrative embodiment of the invention.

' notches.

Referring to FIGURE 6, the fuse adapter of this invention is similar tothe prior art fuse adapters except for the bottom portion, which contains a spacer 40 whose dimensions are selected to positively prevent a 30 amp. fuse from making contact in a 20 amp. fuse adapter. The inside diameter D of spacer 40 is selected to be larger than the outside diameter of the fuse line contact 16 and the holder line contact 24 but smaller than the inside diameter of fuse body 10. Therefore, when a fuse is screwed into the fuse adapter socket of this invention, as indicated by the dashed lines in FIGURE 7, the bottom of the fuse body contacts the top of spacer 40 and the bottom of spacer 44 contacts the bottom of the fuse holder recess. The fuse line contact 16 and the holder line contact 24 extend through the center of spacer 40 and will meet if the length L of the spacer is shorter than the length of fuse line contact 16 plus the height H (FIG- URE 4) of holder line contact 24. Therefore, in accordance with this invention, the length L of spacer 40 is selected to be shorter than the length of fuse line contact 16 plus height H but longer than the length of fuse line contact 16' plus height H. This allows the 20 amp. fuse to make contact in the fuse adapter but positively prevents the 30 amp. fuse from making contact. It should be noted that spacer 40 is loosely fitted into the bottom of shell member 28 so that it can readily slide up and down to allow the fuse adapter to be snapped into the fuse holder. In order for lanced hooks 36 and 38 to be engaged in their corresponding notches 36' and 38, it is necessary to have a small gap 6' between the bottom of the fuse adapter and the fuse holder so that the lanced hooks can be pushed past their corresponding If spacer 40 were rigidly attached to the bottom of the fuse adapter, it would prevent lanced hooks 36 and 38 from being moved past their corresponding notches, and thus prevent the adapter from being easily snapped into the fuse holder.

Spacer 40 can be made of any suitable material, either metallic or nonmetallic, but for each of manufacture and assembly, it is preferably made of brass in the form of a cylinder having a flange at one end only. In this case, the unflanged end of the cylinder is inserted through the hole in shell member 28 from the inside and then peened over to form the lower flange on sleeve member 40. The peening is done over a shim placed against the cylinder on the bottom of shell member 38. The shim, of course, is removed after the peening operation has been completed, and the thickness of the shim will determine the overall length L of the finished spacer. In general, the thickness of the shim should be selected to be equal to the desired overall spacer length minus the thickness of the spacer flanges and the thickness of the bottom of shell member 28. The desired overall spacer length depends on the length of the line contacts of the fuses and fuse holders, as explained earlier.

From the foregoing description it will be apparent that this invention provides a fuse adapter which eliminates all possibility of connecting into an electrical circuit a fuse of higher rating than the electrical circuit. It should also be understood that this invention is by no means limited to the specific embodiment disclosed herein by way of example, since many modifications can be made in the disclosed structure without departing from the basic teaching of this invention. For example, the spacer member of this invention does not have to be formed in the shape of a flanged cylinder; it could be a plain cylinder with holes drilled through the top and bottom to receive stop pins, or it could be flanged at one end and drilled to receive a stop pin at the other end. These and many other modifications of the disclosed structure will be apparent to those skilled in the art, and this invention includes all modifications falling within the scope of the following claims.

I claim:

1. A cup-shaped fuse receiving adapter removably inserted into a fuse holder recess which contains a line contact of predetermined height H above the bottom of the recess, said adapter including means cooperating with said recess for the fixed positioning of said adapter therein, and reqiuring a predetermined initial gap between said adapter and said recess; a hollow spacer'member passing through an aperture in the bottom of said adapterand having two open ends for receiving respectively the line contact of said fuse holder and the line contact of a fuse, said spacer being shorter in axial dimension than the combined height H plus the length of the line contact of a fuse of predetermined rating and longer than the corresponding dimension of higher rated fuses, and means limiting said spacer to a predetermined longitudinal displacement relative to said adapter whereby said spacer may effectively perform its function Without obviating the gap necessary for insertion of the adapter into the recess.

2. The combination defined in claim 1 in which said hollow spacer member comprises flanges at both ends thereof for limiting said spacer member to said predetermined longitudinal displacement.

References Cited by the Examiner UNITED STATES PATENTS 1,832,194 11/1931 Esser 200-119 1,910,482 5/1933 Stoddard 200-119 1,948,421 2/1934 Johnson et a1. 200-l1'9 1,956,337 4/1934 Wood 2001 19 1,969,257 8/1934 Cowles 2001i9 FOREIGN PATENTS 46,456 2/ 1911 Austria.

BERNARD A. GILHEANY, Primary Examiner.

HIRAM B. GILSON, Assistant Examiner.

Claims (1)

1. A CUP-SHAPED FUSE RECEIVING ADAPTER REMOVABLY INSERTED INTO A FUSE HOLDER RECESS WHICH CONTAINS A LINE CONTACT OF PREDETERMINED HEIGHT H ABOVE THE BOTTOM OF THE RECESS, SAID ADAPTER INCLUDING MEANS COOPERATING WITH SAID RECESS FOR THE FIXED POSITIONING OF SAID ADAPTER THEREIN, AND REQUIRING A PREDETERMINED INITIAL GAP BETWEEN SAID ADAPTER AND SAID RECESS; A HOLLOW SPACER MEMBER PASSING THROUGH AN APERTURE IN THE BOTTOM OF SAID ADAPTER AND HAVING TWO OPEN ENDS FOR RECEIVING RESPECTIVELY THE LINE CONTACT OF SAID FUSE HOLDER AND THE LINE CONTACT OF A FUSE, SAID SPACER BEING SHORTER IN AXIAL DIMENSION THAN THE COMBINED HEIGHT H PLUS THE LENGTH OF THE LINE CONTACT OF A FUSE OF A PREDETERMINED RATING AND LONGER THAN THE CORRESPONDING DIMENSION OF HIGHER RATED FUSES, AND MEANS LIMITING SAID SPACER TO A PREDETERMINED LONGITUDINAL DISPLACEMENT RELATIVE TO SAID ADAPTER WHEREBY SAID SPACER MAY EFFECTIVELY PERFORM ITS FUNCTION WITHOUT OBVIATING THE GAP NECESSARY FOR INSERTION OF THE ADAPTER INTO THE RECESS.

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