# US 4,399,402 A · Resistive fault sectionalization

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- Number: US 4,399,402 A
- Document ID: US4399402A
- Status: Granted
- Kind: A
- Application number: 06/298,074
- Filed: 1981-08-31
- Granted: 1983-08-16
- Earliest claimed: 1981-08-31
- Assignees: Bell Telephone Laboratories, Incorporated
- Inventors: James A. Pelletier
- Web page: https://patentgrep.com/patent/US4399402A

## CPC

- G01R 31/083: {in cables, e.g. underground}
- G01R 31/50: Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58)
- G01R 31/52: Testing for short-circuits, leakage current or ground faults
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A methodology, and associated circuitry, for locating a resistive shunt fault coupling the cable shield and the conductors of the cable pair under test comprises the steps of: (i) measuring the open-circuited DC resistance (A.sub.1 and A.sub.2) of the pair from test locations (A and B) which straddle the fault; (ii) measuring the short-circuited DC resistance (A.sub.3) of the pair from one of the test points (A or B); and (iii) evaluating the resistance of one conductor of the pair between the fault and the location of the short circuit measurement according to a predetermined quadratic expression involving the three measured quantities. Sensitivity of the measurement technique is reduced by adding a resistor in series with said pair, at either location A or B, so that A.sub.2 is substantially equal to A.sub.1.

## Claims

### Claim 1

A method for testing a cable pair (TIP,RING) to locate a shunt resistance fault (R.sub.F) between first (A) and second (B) test positions by determining the conductor (TIP or RING) resistance (R.sub.X) between said fault and said second test position, said method
CHARACTERIZED BY THE STEPS OF
measuring the DC resistance (A.sub.1) of said pair at said first test position with said pair open-circuited at said second test position,
measuring the DC resistance (A.sub.2) of said pair at said second test position with said pair open-circuited at said first test position,
measuring the DC resistance (A.sub.3) of said pair at said second test position with said pair short-circuited at said first test position, and
determining the value of said resistance (R.sub.X) from the expression
R.sub.X.sup.2 -A.sub.2 R.sub.X +(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 =0.

### Claim 2

A method for testing a cable pair (TIP,RING) to locate a shunt resistance fault (R.sub.F) between first (A) and second (B) test positions by determining the conductor (TIP or RING) resistance (R.sub.X) between said fault and said second test position, said method
CHARACTERIZED BY THE STEPS OF
measuring the DC resistance (A.sub.1) of said pair at said first test position with said pair open-circuited at said second test position,
adding a preselected resistance (.+-.R) in series with one conductor (TIP or RING) of said pair to form a series combination,
measuring the DC resistance (A.sub.2) of said series combination at said second test position with said pair open-circuited at said first test position,
measuring the DC resistance (A.sub.3) of said series combination at said second test position with said pair short-circuited at said first test position, and
determining the value of said resistance (R.sub.X) from the expression
(R.sub.X .+-.R).sup.2 -A.sub.2 (R.sub.X .+-.R)+(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 =0.

### Claim 3 (depends on 2)

The method as recited in claim 2 further comprising the step of selecting said resistance (.+-.R) so that A.sub.2 essentially equals A.sub.1.

### Claim 4

Testing apparatus for locating a pair fault (R.sub.F) between first (A) and second (B) test positions by determining the conductor (TIP or RING) resistance (R.sub.X) between said fault and said second test location, said apparatus
CHARACTERIZED BY
first means at said first location to sequentially configure said pair (i) for measuring the DC resistance (A.sub.1), (ii) by open-circuiting and (iii) by short-circuiting said pair, respectively, and
second means at said second location, operating simultaneously with said first means, to configure said pair (i) by open-circuiting said pair, (ii) for measuring the DC resistance (A.sub.2), and (iii) for measuring the DC resistance (A.sub.3), respectively, of said pair,
wherein said resistance (R.sub.X) is a solution to the quadratic expression
R.sub.X.sup.2 -A.sub.2 R.sub.X +(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 =0.

### Claim 5

Testing apparatus for locating a pair fault (R.sub.F) between first (A) and second (B) test locations by determining the conductor (TIP or RING) resistance (R.sub.X) between said fault and said second test location, said apparatus
CHARACTERIZED BY
first means at said first location to sequentially configure said pair (i) for measuring the DC resistance (A.sub.1), by (ii) open-circuiting and (iii) by short-circuiting said pair, respectively, and
second means at said second location, operating simultaneously with said first means, to configure said pair (i) by open-circuiting said pair, (ii) by adding a preselected resistor (.+-.R) in series with one conductor of said pair and measuring the DC resistance (A.sub.2) of the series combination, and (iii) by measuring the DC resistance (A.sub.3) of said combination,
wherein said resistance (R.sub.X) is a solution to the quadratic expression
(R.sub.X .+-.R).sup.2 -A.sub.2 (R.sub.X .+-.R)+(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 -0.

### Claim 6 (depends on 5)

The apparatus as recited in claim 5 wherein said resistor (.+-.R) is chosen so that A.sub.2 essentially equals A.sub.1.

### Claim 7

Wire-pair apparatus for testing a resistive fault (R.sub.F) located between first (A) and second (B) test locations and for determining the resistance (R.sub.X) of one wire (TIP or RING) between said fault and said second test location, said apparatus
CHARACTERIZED BY
first means at said first location having three sequential modes of operation including: a first mode for measuring the DC resistance (A.sub.1) of said pair; a second mode for disconnecting said first means from said pair; and a third mode for shorting said pair, and
second means at said second location operating in one-to-one correspondence to said modes for: disconnecting said second means from said pair during said first mode; measuring the DC resistance (A.sub.2) of said pair during said second mode; and measuring the DC resistance (A.sub.3) of said pair during said third mode,
wherein said resistance (R.sub.X) is a solution to the quadratic expression
R.sub.X.sup.2 -A.sub.2 R.sub.X +(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 =0.