Presented by: H.J. Arnett Industries, LLC 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. Battery +/- Lead (-) (+) D.C. SCOUT LOAD Building Ground Lead Current Flow 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 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. Pulse Detector Battery +/- Lead (-) (+) A B D.C. SCOUT LOAD C Building Ground Lead Current Flow Note that the ground detection system battery is the source of the current flow, not the Scout. 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. 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 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. 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 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 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 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 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 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 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. 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. 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. 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. 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. 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. 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. Scout’s 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. Scout’s pulse, which is not circulating on both the (+) and (-) wires. 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. Scout’s 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 Scout’s pulses stand out from the existing noise. 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. 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.