Note: Descriptions are shown in the official language in which they were submitted.
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CABLE TEST SET
TECHNICAL FIELD
The present invention relates to product quality and
safety testing of circuit size electrical cable having
plural conductors. More particularly, the present
invention relates to an apparatus and method for testing
the continuity and insulation leakage integrity of such
cable.
BACKGROUND ART
Various local and governmental standards authorities
have established standards that require certain electrical
cables to be subjected to continuity and insulation
leakage integrity testing before sale to the public. When
each marketable length of cable must be tested, the
process is labor-intensive and adds significantly to the
product cost. Previously, the cable was tested manually
by first connecting the respective ends of the cable to a
voltage source and a lamp or meter for indicating
electrical continuity through the individual wires
comprising the cable. Thereafter, any electrical
insulation leakage integrity between electrical wires was
tasted by means of a megohmmeter or the like to indicate
electrical insulation leakage integrity faults or failure.
Only a limited number of lengths of cable could be tested
per hour by any one person with such an apparatus.
MoreoverP if high voltages were involved, the testing
personxiel would be subjected to safety hazards if the
cables were mishandled.
Since the operating and test voltage standards may
vary in different areas, the test voltage level must be
adjusted to the desired values.
The present invention organizes and regiments the
testing equipment and test procedures to ensure rapid and
efficient compliance with the best standards and with
maximum test personnel safety.
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DISCLOSURr ON INVENTION
In view of the foregoing limitations and shortcomings
of the prior art testing methods and procedures, as well
as other_ disadvantages not specifica:Lly mentioned above,
it should be apparent that there exists a need in the art
for an improved apparatus and method for testing circuit
size electrical cables having multip:Le conductors.
More particularly, the present invention organizes
the apparatus and the steps of the standards testing in a
form which ensures efficient and safe testing of the
object cables.
It is, therefore, a primary object of this invention
to fulfill that need by providing a first apparatus for
testing circuit size electrical cable having plural
conductors, which includes: a voltage source of a first
level; apparatus for adjusting said voltage to test
voltage levels; a device for indicating the presence of
said test voltage levels; apparatus for selectively
connecting said test voltage levels to the individual
conductors of said cable; and a device for selectively
switching said voltage levels to said connecting device at
different switching device positions; wherein said
indicating device is adapted for connection through said
switching device, said indicating device, and said
individual ones of said conductors of said cable to said
voltage levels to indicate continuity in respective ones
of said conductors in a first switch position and an
electrical leakage integrity path between two or more
conductors in another switch position. ~ voltage meter or
other indicator may be included to indicate specific test
voltage levels.
The objective of the invention may also be
accomplished by providing an apparatus for testing circuit
size electrical cable having plural conductors, including:
a first voltage source; a test voltage source; first
device for indicating the presence of said test voltage;
second device for indicating the presence of said first
voltage; a relay device for selectively connecting said
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second indicating device and said first voltage source;
apparatus for selectively connecting said test voltage to
separate conductors of said cable; and a device for.
selectively switching said test voltage to said connecting
apparatus at different switching device positions; wherein
said first indicating device is adapted for connection
through said switching device and said first indicating
device to individual conductors of said cable to said test
voltage to indicate electrical leakage integrity between
said individual conductors in a first switch position, and ,
wherein said second indicating device is adapted for
connection to said first voltage through respective ones
of said conductors via said relay device under control of
said switching device to indicate continuity of individual
conductors in another switch position.
Tn apparatus for testing circuit size electrical
cable having plural conductors, the objective of the
invention can be achieved by the test method which
includes the steps of providing d first voltage;
selectively connecting ends of individual ones of the
conductors to the fixst voltage thraugh the contacts of a
relay and an indicator in series therewit~i via a switch
controlling said relay in a first switch position to
indicate electrical continuity of each conductor; noting
the-indicator response for each conductor; providing a
test voltage; selectively connecting separate conductors
in a second switch position to said test voltage via an
indicator and said switch in a second position to indicate
an electrical leakage integrity path among said
conductors; and noting the indicator response for each
combination of two conductors.
With the foregoing and other advantages and features
of the invention that will become hereinafter apparent,
the nature of the invention may be more clearly understood
by reference to the following detailed description of the
invention, the appended claims, and the view illustrated
in the attached drawing.
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BRIEF DESCRIfZ'ION OF DRAWING
FIG. 1 is a schematic diagram i_l.lustrating an example
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
There is shown in FIG. 1 an embodiment of the present
invention suitable for testing circuit size electr.i.cal
cable 12 having plural conductors, or wires. Such cables
are also known in 'the art as building wire or non-metallic
sheathed cable. Each cable is composed of at least two
circuit conductors 16, 18, which are conventionally
longitudinally encased within plastic electrical
insulation 30, and at least one ground wire 14, which is
often uninsulated. A third circuit conductor 20 may be
included; when such is supplied, it is also usually
insulated. Occasionally, a cable may be encountered which
does not include the ground wire 14. At least a portion
of the ground wire may be wrapped with a paper wrapping
(not shownj. A longitudinal reinforcing material may also
be included.
The two specific electrical tests for which this
apparatus and method are intended include continuity, here
defined as the substantial electrical conductivity of the
wire, and electrical insulation leakage, defined here to
refer 'to an unacceptable electrical current path between
pairs of wire conductors.
A source of voltage 22 is provided to the test
apparatus 10. The present invewtion contemplates use of
ordinary electrical AC mains voltage as source 22. DC
voltages may be used with. appropriate circuit equivalents
and substitutes for AC specific elements described in the
exemplary embodiment.
Often, the test voltage level desired is other than
that conveniently available from the AC mains. Tn such
situations, a means for adjusting the voltage to the
required test levels must be provided to accommodate this
voltage difference. In the present.embodiment, an
adjustable transformer may be used, shown here
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schematically as autotransformer 24. A Powerstat Model
~klOC autotrans.former may be used with AC mains voltage
levels in the range of from about 9U to a-t least about 150
volts to produce a test voltage level of from about 0 to
at least about 150 volts.
A meter 50 may be convenient to indicate the voltage
level available from the autotransformer 24. Safety
precautions commensurate with good engineering practice
should be followed. A power ON/OFF switch 32 and a fuse
34 or.other circuit overload protection device may
therefore be incorporated into the primary circuit of the
autotransformer, as shown. Appropriate grounding of
exposed metal cabinet parts should be arranged to minimize
personnel injury hazards. It may also be convenient to
include a POWER ON indicator such as lamp 36 to indicate
when the test apparatus is energized, as potentially
lethal voltage levels are anticipated.
The present embodiment includes separate indicators
for the continuity test and for the electrical leakage
integrity test; however, a single indicator could be used
as explained hereinafter. For the purposes of this
illustrative example, individual red incandescent lamps
are used to indicate failure of a cable to pass the
respective continuity or electrical leakage integrity
test. Other indicators and other lamp colors may also be
used.
A first lamp 26 for indicating electrical leakage
integrity failure is connected between the autotransformer
24 secondary winding and a pair of test leads 28, which
are to be connected to the cable conductors under test,
via switch 42 in.the "LEAKAGE" test position 46.
When internally set to test electrical leakage
integrity, each of the test leads 28 is connected to
different conductor at ane end thereof, ixsually the
beginning or the end of the cable 12. Then, when switch
42 is placed in the "LEAKAGE" position, a complete
electrical path is formed only when a low resistance path
is provided between the two conductors, such as occurs
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with defective insulation 16 on the conductors. Such a
defect results in a short circuit, connecting the
indicator lamp 26 to the test voltage source 24 and
lighting the indicator 26. Two of the conductors 14, 16,
18, 20 are connected at a time and 'tested in pairs. Thus,
each of the conductors 14, 16, 18, and 20 in a given cable
12 is tested in this way in combination with each of the
other conductors in the cable to ensure absence of
electrical leakage between the wires.
A second lamp 38 for indicating continuity failure is
connected across 'the AC mains via normally-open contacts
48 of a relay 40. The relay coil (not shown) is operated
via.a pair of test leads 28, which are to be connected to
the ends of a conductor (14, 16, 18, or 20) in the cable
12 under test, via switch 42 in the "CONTINUITY" test
position 44.
Switch 42 is shown as a double-pole, double-throw
switch, with each of the test leads (28) connected to one
of the respective common poles of the switch. One
switched pair of poles is connected to the autotransformer
24 output. The remaining pair of switched poles is
connected to a relay, as will be discussed subsequently.
Those of ordinary skill in the art will recognize that a
double-pole, double-throw relay and appropriate control
circuit may be substituted for the switch, the switch
version being shown here for simplicity.
When internally set to test continuity, each of the
test leads 28 is connected to wn opposite end of a given
wire conductor 14, 16, 18, 20, placing the conductor in
series with the internal operating coil (not shown) of
relay 40 and completing thereby a circuit path across -the
source voltage. Relay 40 may be, for example, a MEK Model
54 transistorized relay with at least one set of normally
open contacts 48. When switch 42 is placed in the
"CONTINUITY'° position 44, a complete path is formed which
includes the relay coil to activate the relay 40 and close
contacts 48, connecting the indicator lamp 38 to the AC
mains voltage source and lighting 'the indicator. Each of
the conductors in a given cable is tested in this way to
ensure full continuity of the wires.
Each of the two switch 42 positions corresponds to
one of the cable tests. When switch 42 is in the position
labeled "CONTINUITY" 44, the cable conductor continuity is
tested. When switch 42 is in the po:oition labeled
"LEAKAGE" 46, the cable conductor electrical leakage
integrity is tested. Though not sho~m, a center-off
switch could be substituted, having a third position which
could be labelled "OFF" or the like.
One of ordinary skill in the art will recognize that
a variation of the switching circuit, especially suitable
when a relay is used in place of switch 42, would be to
substitute a four-pole, double-throw contact arrangement
in which the common poles of the extra double-pole,
double-throw contacts are connected to a single indicator
to signal a failure. In this configuration, the switched
extra pairs of. poles.are connected, respectively, to
points 52, 54 and 56, 58 in place of the separate
indicator lamps 26, 38. In this manner, a single
indicator or lamp can be alternately connected to indicate
failure.of the cable for both of the functions being
tested.
A cable may be tested for continuity by a method
which includes both continuity tests and leakage integrity
tests. This is accomplished by first supplying a voltage
such as AC mains voltage from a source at 22, connecting
the test leads 28 to the ends of individual conductors and
then placing the switch 42 in the "CONTINUITY" position 44
with the source voltage applied, noting the response of
indicator lamp 38, and subsequently repeating this process
for each conductor of the cable. The cable may then be
tested for electrical leakage integrity by supplying a
test voltage, such as 100 volts AC or such other voltage
level as may be required, from a source at 24 (the voltage
level from which may be adjusted as required), connecting
the test leads 28 to an end of each of two individual
conductors in pairs of conductors and then placing the
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switch 42 in the "L>;AKAGK" position 46 with the source
voltage applied, noting the response of indicator lamp 26,
and subsequently repeating -this process for each
combination of two conductors in the cable.
Although certain presently preferred embodiments of
the invention have been described herein, it will be
apparent to those skilled in the art to whidh the
invention pertains that variations and modifications of
the described embodiment may be made without departing
from -the spirit and scope of the invention. Accordingly,
it is intended that the invention be limited only to the
extent required by the appended claims and the applicable
rules of law.
