The D.C. Scout Battery Distribution System Ground Locator

1
The D.C. Scout Battery Distribution System
Ground Locator

• Presented by H.J. Arnett Industries, LLC

2
D.C. Scout Purpose

• The D.C. Scout is used for locating resistive or
  non-resistive current paths from DC Battery
  Distribution System to building ground without
  de-energizing components or loads in the system.

3
D.C. Scout Description

• Instrument consists of two basic parts
• A) Pulser Unit, used to pulsate current through
  the DC battery DC Scout building ground loop
• B) Pulse Detector Unit, used to detect pulses
  generated by the Pulser Unit in the DC battery
  DC Scout building ground loop

4
Operational Overview

• The D.C. Scout repeatedly opens and closes
  (pulses) the closed circuit, established when
  D.C. Scout is connected. Current flows from the
  () battery pole, through the wire shorted to
  building ground, through the D.C. Scout building
  ground lead, then back through the D.C. Scout /-
  battery lead to the negative battery post.
• Note that the ground detection system battery is
  the source of the current flow, not the Scout.

5
Operational Overview

• The D.C. Scout Detector Unit can then detect and
  show these pulses on the Detector Unit Meter
  where the Pulse Detector Current Transformer
  Probe is clipped over a wire in the current path.
• This systematic approach of noting where pulses
  have been detected, then moving down the wire to
  where pulses are not detected, pinpoints the
  ground fault location.

6
D.C. Scout Precautions

• Always wear proper Personal Protection Equipment
  when working on and around energized circuits
• Work involves energized circuits
• Inspect all energized equipment for proper
  installation and functions before initializing
  work

7
D.C. Scout Limitations

• D.C. Scout Pulser Unit should be connected in
  parallel with grounded circuit (positive or
  negative ground) it will have full battery
  voltage across it for a solid ground or partial
  voltage across it for a resistive ground.
• Pulse amplitude will be set for a minimum of 5 mA
  to a maximum of 200 mA DC.
• D.C. Scout Pulser Unit has two in-line fuses to
  ensure protection of D.C. Scout and system it is
  analyzing. If more sensitive protection is
  desired, a lower amperage quick-blow fuse may be
  substituted this would limit output capacity of
  D.C. Scout.
• Under no circumstances should a fuse rating of
  more than 250 mA be installed in BATT FUSE or
  GRND FUSE fuseholders.
• With both Switches A and B on, there is no
  current limiting resistors in circuit and it is
  possible to quickly blow D.C. Scout Pulser Units
  BATT FUSE or GRND FUSE.

8
Operation Instructions

• Follow all tag out and safety procedures for
  working on energized circuits.
• Ensure all systems operators are aware of fault
  situation and procedures to follow
• Determine if Ground is Positive () or Negative
  (-)
• Controls on D.C. Scout Unit will be set to locate
  the problem. If it is a Positive Ground, set
  controls to () GRD, or (-) GRD

9
Operation Instructions

• Set controls on the pulser unit as follows
• If ground is positive (), set Meter Switch C to
  ().
• If ground is negative (-), set Meter Switch C to
  (-).
• Set pulse amplitude adjust control to minimum
  current position.
• Set pulser ON/OFF switch to OFF.
• Verify fuses for battery fuse and ground fuse are
  100 mA (1/10A).
• Plug in D.C. Scout pulser Unit 120 VAC power
  cord.

Meter Switch C-Positive or Negative Ground Switch
10
Operation Instructions

• Set controls on the Pulser Unit as follows
• If ground is positive (), connect D.C. Scout
  Pulser Unit as follows
• Connect black BLDG GROUND lead to building ground
  wire.
• Connect red BATT. /- lead to negative (-) bus.
• If ground is negative (-), connect D.C. Scout
  Pulser Unit as follow
• Connect black BLDG GROUND lead to building ground
  wire.
• Connect red BATT. /- lead to positive () bus.

Negative Bus Connection
Building Ground Connection
11
Operation Instructions

• Adjust D.C. Scout Pulser Unit as follows
• NOTE A solid ground has zero resistance to
  ground. A resistive ground will show up on both
  positive and negative indicators, but one will
  show more strongly than other.
• If system voltage is 24, 48, 125 VDC with a solid
  ground
• Set Switch A - ON (closed).
• Set Switch B - OFF.
• Set 5K/55K switch to 5K.
• Set 30mA/300mA meter range
• switch to 300mA.

Switch A and B
12
Operation Instructions

• Adjust D.C. Scout Pulser Unit as follows
• If system voltage is 250 VDC with a solid ground
• Set Switch A - OFF.
• Set Switch B - OFF.
• Set 5K/55K switch to 5K.
• Set 30mA/300mA meter range
• switch to 300mA.

Switch A and B
13
Operation Instructions

• Adjust D.C. Scout Pulser Unit as follows
• If system voltage is 24, 48, 125 or 250 VDC with
  a resistive ground
• Set Switch A - OFF.
• Set Switch B - OFF.
• Set 5K/55K switch to 55K.
• Set 30mA/300mA meter
• range switch to 30 mA.

Switch A and B
14
Operations Instructions

• The D.C. Scout package has an External Pulse
  Indicator Lamp. This lamp is handy for seeing
  when each pulse from the Pulser Unit occurs, even
  when the user may be 40 yards or more away from
  the Pulser Unit.
• Plug the External Pulser Lamp jack into the
  Pulser Unit External Lamp Output plug. The lamp
  has velcro backing to place it in the upper right
  side of the units lid when open.

15
Operation Instructions

• Set up D.C. Scout Pulse Detector Unit as follows
• Plug pulse detector unit current transformer
  probe into banana jacks of on back of Pulse
  Detector Unit.
• Turn on pulse detector unit by pulling out on
  balance control knob.
• Adjust balance control until meter needle is
  centered on meter.
• Perform a battery check by pressing red button on
  back of unit meter needle should deflect to BATT
  OK position on meter face.
• Clamp current transformer probe around red BATT
  /- lead of pulser unit.

16
Operations Instructions

• Set pulser ON/OFF switch to ON.
• NOTE If turning on pulser causes any relay
  actuations, this relay and its wiring should be
  thoroughly investigated to ensure these
  components are not the cause of ground fault.
• Adjust pulse frequency adjust control for desired
  pulse rate. Slowest rate is a good place to
  start.
• CAUTION Do not adjust pulse amplitude to exceed
  100 mA.
• NOTE Meter range switch may be changed to
  either scale as required for adjustment.
• Using pulse amplitude adjust control, adjust
  pulse meter to read a minimum of 5 mA to a
  maximum of 100 mA.

17
Operation Instructions

• NOTE In some cases, DC Scout Pulser Unit Pulse
  Meter will not register minimum detectable ground
  current of 4 to 5 mA (i.e., a highly resistive
  ground). For this reason, manufacturer specifies
  DC Scout is only effective for use on ground
  currents that generate ? 5 mA reading.
• If a minimum of 5 mA cannot be obtained, perform
  following
• Turn pulse amplitude adjust control to minimum.
• Set both Switches A and B to ON.
• Slowly adjust pulse amplitude adjust control to 5
  mA.

18
Operation Instructions

• The Pulse Detector unit meter needle should begin
  deflecting left and right.
• Adjust sensitivity knob, on back of pulse
  detector unit, for a wide deflection both ways
  from center mark on meter scale.
• Clamp pulse detector probe around load wires to
  trace pulse to grounded circuit.
• The Pulse Detector Unit meter needle should now
  be deflecting right then left of the meter center
  for each Pulse Unit pulse. If the meter needle
  deflects to the left on each pulse, reverse the
  clamp on direction of the Detector Unit Probe.

19
Tracing the Fault

• Expose the load wire in the distribution panels,
  using caution to avoid tripping any circuit
  breakers or disconnecting switches.
• Clamp the Detector Probe around each load wire
  and note the wire or wires, which have pulses
  that coincide with the generated pulses.
  Determine the locations of the panels or devices
  these circuits feed. Continue to follow the
  pulses until the grounded wire or device is
  found. BE SYSTEMATIC AND USE YOUR PRINTS.

20
Usage Tips

• At times there can be difficulty discerning
  between the desired pulses on the Detector Meter
  and random pulses, or noise.
• For those pulses/spikes, which are circulating
  from (-) to () in the circuit, clamp the D.C.
  Scouts Pulse Detector Probe around both (-) and
  () wires at the same time. The circulating
  pulses will cancel out and you should see only
  the D.C. Scouts pulse, which is not circulating
  on both the () and (-) wires.

21
Usage Tips

• For those pulses/spikes that are radiating down a
  wire and are not circulating, move down the wire,
  if possible, to get away from noisy systems such
  as choppers, and inverters. It may be necessary
  to decreases the sensitivity of the Pulse
  Detector and increase the amplitude of the D.C.
  Scouts pulse in order to override the remaining
  interference.
•  
• The Pulse Frequency Adjust control on the D.C.
  Scout Pulser Unit can be adjusted so that the
  frequency of the Scouts pulses stand out from
  the existing noise.

22
Additional Applications

• Locating A.C. Grounds
• The D.C. Scout can be used to locate grounds on
  A.C. system up to 480 volts, provided the
  following conditions are met.
• The A.C. circuit must be totally de-energized and
  disconnected from its source. This means all
  phase leads and the neutral lead, if used.
• A 130 Volt D.C power supply must be available
  that is capable of supplying 200 mA of current.
  This D.C. voltage must be isolated from ground.
  This means that the () and (-) leads each read
  zero (0) volts to ground when energized.

23
Additional Applications

• Ground locating on Fire Alarm and Marine Systems
• The D.C. Scout has been used successfully to
  locate grounds on fire alarm systems, using the
  procedures outlined.
• These procedures will be useful for marine
  systems as well.
• We welcome comments, reports, and questions from
  users.