3 965ams fault locating overview presented by gary morris

3965AMS

Fault Locating Overview

Presented by

Gary Morris

Outline

• Fault Locating – RFL– TDR

Fault Locating• When to Use TDR and RFL• Opens and TDR for Capacitive Faults• RFL and TDR for Resistive Faults

When to Use TDR or RFL

• You should know what fault or condition you have before trying to isolate with the RFL or TDR.

TDR RFL

Load Coil Yes No

Tip/Ring Open Yes No

Water Yes No

Bridge Tap Yes No

High Res Opens Yes No

Short = or < 500 Ohms Yes

Tip Ground No Yes

Ring Ground No Yes

Battery Crosses No Yes

TDR

• Press the TDR key• Choose Setup to enter cable information.• When finished choose a test and press OK

TDR Trace Examples - Open

• Here is a pair the is open at 1780 feet.

TDR Tip Open

• Here is a pair the has an open tip open at 780 feet.

TDR Series Resistance

• Here is a pair the has a high resistance open at 950 feet.

TDR Short

• Here is a pair the has an short at 1000 feet.

TDR Water

• Approximately 100 Feet of water.

Expert Pair Test

1. RFL test is used for faults under 20 mΩ.

2. Always draw a diagram of the fault for better analysis.

3. There three factors that is always involved in RFL (Resistance Fault Locating) - Gauge, Length and Temperature of the cable. Any two of the three must be known for RFL to work. The best option is to know the Gauge and Length of the section under test and the test set will compute the cable temperature. This is done during RFL Setup.

4. A pair may have some light faults in it but it can be used as a ‘Good Pair’ as long as the light fault is at least 200 times better than the magnitude of the fault in the faulted pair. Ex: If the fault on a pair is 1 kilo-ohms, a pair with a 200 kilo-ohm fault can be used as a good pair. Of course, the higher the magnitude, the better.

5. For best RFL accuracy , make a long cable section shorter by going to the middle of the section and open the pair to cut it in half. Check for the fault in one direction and then the other and then isolate the clean side. Repeat the process until the cable section becomes short enough where the following becomes practical:

a) the length of a short section can easily be measured physically with a roller tape. If gauge and section length are known, the test set will compute cable temperature.

b) With a short cable section, the use of a reel of jumper wire as a “Good Pair” placed above ground is now possible, instead of digging into the cable for a good one. Saves time. With a separate good pair and knowing the gauge and length of the section is the best and most accurate RFL option.

6. In a ‘Single Pair Hookup’, the best good conductor to use is the mate of the faulted one and the next best is any good conductor from any of the adjacent pairs in the same group. Ex: If a pair has TIP(A) is

faulted and RING(B) is good, RING(B) is then the best good conductor to use to shoot the fault on TIP(A).

7. If DTF (Distance-To-Fault) and DTS (Distance-To-Strap) are equal, the fault is either at the strap or beyond.

RFL Fault Locating Tips

The use of a

“Separate Good Pair”

is always the most accurate way to

locate any type of a resistance fault.

RFL TIPS

Resistance FaultsGROUND : A fault between ‘Tip [A]’ and ‘Ground’, ‘Ring [B]’ and ‘Ground’ or both conductors and ‘Ground’.

Resistance Faults Cont..SHORT : A fault between ‘Tip [A]’ and ‘Ring [B]’ conductors.

Resistance Faults Cont..Battery CROSS : A fault between a working pair and a non-working pair (pair under test).

Pair # 1 - Working pair

Pair # 2 - Non-working(Pair under test)

-48 VDC

-46 VDC

Solid Cross FaultWater

-48 VDC

-7 VDC

Resistive Cross fault

Pair # 1 - Working pair

RFL Hookup Examples


It can be any pair of any gauge, longer or shorter than the faulted one,

it doesn’t matter.

For short cable section lengths (1000 feet or less), the good pair can be a

reel of a CO jumper wire or a telephone jacketed wire placed above ground.

Reel of CO jumper wire

or

telephone jacketed wire

Good Pair

Faulted Pair Strap

End-1

End-2

Ground Fault

Shield/GroundNear-End Far-End

Good Pair


It can be any pair of any gauge, longer or shorter than the faulted one,

it doesn’t matter.

For long cable section lengths (several thousand feet), the good pair can come

from another cable adjacent to the cable with the faulted pair.

Good Pair

Faulted Pair

Common

End-1

End-2

Near-End Far-End

Good Pair

Faulted Pair

Strap

Short

Fault

How To Extend The “Far-End Strap” If Necessary

Reel of CO jumper wire or telephone jacketed wire or any two wires, same length

(any gauge)

Faulted Pair

Far-End Strap

End-1 End-2

Short

Near-End

Common

Good Pair [ from a distant cable ]

Strap extension

Far-End

RFL Single Section Setup

T-GR-GShortTip CrossRing CrossWet Pulp

Choose fault type.

Choose single pair or separate pair.

Select single or multiple section.

Choose the gauge.

Length or temperature must be “unknown.”

RFL Multiple Section Setup

T-GR-GShortTip CrossRing CrossWet Pulp

Choose fault type.

Choose single pair or separate pair.

Select single or multiple section.

Choose the gauge.

Length or temperature must be “unknown” on last section.

Aerial Cable:

1. If cable is not in direct sunlight. Add 20oF to the air temperature.

2. If cable is in direct sunlight. Add 40oF to the air temperature.

Buried Cable:

1. Use temperature of tap water (city water). Let water flow out of a water faucet for several minutes and then measure the temperature.

2. In cold climates, use soil temperature at cable depth.

Estimating Cable Temperature

RFL Cont..

Press setup to change section 1 from 24 awg to 26 awg.

3640.8 ft

3406 ft234.8 ft

Distance To Strap (DTS) = 4000 feetDistance To Fault (DTF) = 2500 feetStrap To Fault (STF) = 1500 feet

The bridge tap does not affect this reading.

1000 ft 3000 ft

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1000 ft 3000 ft

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Fault measures here!

1000 ft 3000 ft

500 ft

400 ft

Questions ?

• Live Demo

• 1-800-426-8688 Option 3

3 965ams fault locating overview presented by gary morris

Documents

faulted pair

nonworking pair pair

expert pair testrfl

ohm fault

single pair hookup

short cable section

short section

best good conductor