Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROU'.~ID OF TH~ IIiV13~i'rIOi~i
~ield ol the Invention
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This invention relates to electrical power plugs
and, more particularly, to an electrical power plug having an
internal fuse in series with the power line and the prong
connector.
Description of the Prior Art
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Electrical fuses are in common use for protecting ;~
electric circuits in the event of a short circuit~ Normally,
such fuses are found at a central terminal box for protecting
a large number of electrical outlets or are contained within `-
the electrical device being protected. However, these prior
art fuses cannot be used in ma~ applications, either because
the electrical device is not capa~le of holding a fuse or the
electrical device is connected to electrical outlets havin~
unknown current ratings. In particular, it is o~ten desirable
to place a fuse in series with a string of Christmas lamps.
~owever, the lamps themselves are not large enough to hold a
coRventional fuse and~the fuse rating of the soc~et to which
the string of lar,lps i9 connected is often unknown. Compounding
this problem is the practice of placing a large nurnber of such
strings in series. ~
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Placing a fuse in series-wi~h a string of Christrnas
lights ia desirable for reasons of economy as well as safety
since a safety cer~ification can be obtained~using a smaller
gauge wire in the circuit i~ the circuit also con~ains a ~useO ~ ~
This allows the use of a thinner wire wikhout sacrificing ~ ~ -
safety, a feature which is particularly important in the field-
of Christrnas tree decorations since~a thin wire is easier to
hide~among the branches~and is~also less expensive. The high
flammability o~ such Chri~stmas trees~also mak~s saf~ty the
factor of primary importanc~
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SUM~RY OF THE INVENTION
It is an object of the present invention to provide an
electrical plug containing a fuse which is easily replaced.
It is another object of the present invention to
provide such a fuse which is relatively inexpensive.
It is a further object of the present invention to
provide a fuse which is extremely compact, thereby maintain-
ing the plug at a conventional size.
It is still a further object of the present invention
to provide a fuseable electrical plug which is inherently reli~
able yet inexpensive to manufacture~
These and other ob~ects of the present invention are
provided by an elongated fuse holder carrying a wire fuse ele`-
ment extending beyond each end of the fuse holder. One end of
the wire fuse rests against a planar contact plate connected
to a conventional electrical prong adapted to be inserted in a
wall socket. The other end of the wire fuse is held against
a terminal which has been crimped to the end of the power line.
The fuse holder is extremely compact and is held in
place in parallel alignment with the electrical prong, thereby
insuring a compact configuration. The fuse element consists
only of a wire, and no soldering or special manufacturing pro-
cesses are needed. Thus the fuseable electrical plug of the
present invention is inexpensive to manufacture and the fuse
is readily replaceable. Furthermore, the simplicity of the
- design insures that the plug is inherently reliable.
BRIEF DESCRIPTION OF T~E DRAWINGS
Fig. 1 is an isometric view of the fuseable plug of
the present invention shown as assembled.
`~ 30 Fig. 2 ls an exploded isometric view of the fuseable
plug of the present invention.
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Fig. 3 is a top plan view of the fuseable plug of
the present invention.
Fig. 4 is a cross-sectional view of the fuseable plug
of the present invention taken along the lines ~-4 in Fig. 1.
; DETAILED DESCRIPTION OF THE INVENT:[ON
Referring now to the drawings, the plug housing 2
contains a pair of prong recesses ~1 adapted to receive the
prongs 24 and allow the ends thereof to pass through the end
of the plug housing 2. The prongs 24 have formed thereon a --
plug tab 28 for contacting the prongs of an add-on plug which
may be inserted at the rear of the plug housing 2. The plug
housing 2 contains an add-on plug recess 6 for allowing entry
of the add-on prongs tnot shown) into the plug housing 2. Each
of the prongs 24 contains a planar contact plate 26 which ex-
tends from the prong 24 at a right angle.
The plug housing 2 also contains fuse recesses 8
for allowing insertion of fuse holders 30. The fuse holder 30
is an elongated rectangular plane of plastic having integral
tabs at each end, each of which contains a bore through which
a wire fuse element 32 is inserted and an angled corner 50
corresponding to an angle on the corner of the fuse recesses 8
for insuring that the fuse holder 30 is properly oriented while
being inserted into the fuse recess 8. Each end of the fuse
element 32 is then bent over each end of the fuse holder 30.
The fuse element 32 can be formed from any electrical con-
ductor having a known resistance and a known melting point.
The fuse element 30 will have various current ratings, depend-
ing upon the diameter of the wire that constitutes the fuse
element 32. The diameter of the bores in the tabs is not
critical and, therefore, a wide variety of wire diameters may
be accommodated for a given sized bore. The fuse holder 30
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is inserted into the fuse recess 8 until the end of the fuse
wire 32 rests against the contact plate 26.
As best sho~m in Fig. 3, a pair of insulated leads
18 enter the plug housing 2 at a wire port 16 and enter grooves
14 which guide the lea~s 18 to the proper location. The leads
18 are forceably inserted in the yrooves 14 to cause the leads
18 to be frictionally held in place. For this reason, the
grooves 14 provide strain relief so that the leads 18 camlot
be forceably removed from the plug~ A contact 22 is secured
to the conductors in the insulated leads 1~, either by crimp-
ing or solderin~. The contacts 22 are held securely in place
above the end of the fuse holder 30 by the yrooves 14. The
contacts 22 are separated from each other by a projection 20
which, as will be explained hereinafter, also insures precise
alignment of the cover 34 with the plug housing 2. The fuse
holder 30 is easily re~oved from the plug housing 2 by forcing~
the ends of the pronys 24 into tne plug housing 2, tl~ereby
forcing the fuse holder 30 out the other end of the plug
housing 2 by the contact plate 26. A new fuse wire 32 is
then cut to length and inserted through tne holes at each end ~ ~-
of the fuse holder 30 and bent over each end. Finally, the
~ fuse holder 30 is reinserted in~ the fuse recess 8 after the
end of the prong 24 has been-puIled back to its original
~positîon.
~ cover 34 is secured to thè plug housing 2 by~
screws~46 which extend through the screw holes lO~in the plug
~ housing 2 and engage the threaded bores~36 in the cover 34.
-~ The cove~34 contains an aligmnent slot 42 which receives the~
~alignment projection 18 on the plug housing 2 to insure that ;
~the rotational position between the cover 34 and the plug ;
housing~2 is correct. Further alignr,lent is provided by pro-
jections~38 in the cover 34 which are inserted inta cylLndri-
cal racesses 12 in axial alig~ment with the screw holes 10
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and tab 39, which fits into recess 41. The cover 34 further
includes contact projections 40 which hold the contacts 22
against the ends or the fuse holder 30 to insure conduction
between the contacts 22 and the Euse wire 32. The fuse holder
30 is formed from a resilient plastic which, when compressed
between the contact projections 40 and the contact plates 26,
forms an arc to maintain the ends of the fuse wires 32 in
contact with the contact plates 26 and contacts 22.
The cover 34 further includes a pair of add-on plug
slots 44 through which the prongs of another plug (not shown)
can be inserted to enter the add-on plug recesses 6 and con-
tac~ the plug tab 28, integrally formed from the prongs 24.
In this way, a plurality of plugs may be serviced from one
socket. Note, however, that the add-on plugs will not be
protected by the fuse of the present invention.
- Although the fuseable electrical plug of the present
invention has been described as having a fuse in series with
} each prong 24, adequate short circuit protection can beobtained by including a fuse in series with only one of the
prongs. In this case, the non-fused prong will be identical
to those in conventional use. Thus, it is to be understood
that the present invention is not to be limited to the precise
structure disclosed.
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