Discontinued

BGFT battery ground fault tracer

We always recommend that you characterise the fault. Some faults are purely resistive so tracing the fault is relatively straightforward. The difficult faults have a capacitive element. In these cases, you must balance out this capacitive element to trace the correct path. If you do not do this, you will be tracing phantom faults and may never find the true earth/ground fault.  

An earth/ground fault is a fault to earth. Earth/ground faults can be either low resistance or high resistance in nature. These faults can be caused by insulation failures on worn insulation that allows water ingress. This is why the number of earth/ground faults typically increase after a rainstorm. Other causes of earth/ground faults can include pinched wires and electrolyte leakage. Earth/ground faults can cause nuisance trips and safety hazards and damage equipment.

There can be multiple earth/ground faults in the system. Since current follows the path of least resistance, you will be tracing the path with the lowest resistance. Once this earth/ground fault is fixed, current will follow the other paths and these need to be traced and eliminated systematically. 

You can use the following shortcuts to save time when locating earth/ground faults:

1. A typical utility environment will have four main DC panels represented by one earth/ground recorder. If physically possible, check the main cables or bus work feeding each cabinet (negative and positive) for the injected signal.
2. If you observe a significant imbalance of injected signal with the receiver, start with the cabinet containing the largest signal level. You can use the feedback circuit, but remember that the resistance found is a total of all feeder resistances in parallel.
3. If a main feeder cable having earth/ground current is detected, and you trace the cable to a cabinet with many jumpers, divide and conquer. Move the receiver to a distance halfway from the last measurement point until the fault current disappears and reverse direction until the fault is located.
4. Moving the transmitter every time you relocate to another cabinet during tracing is unnecessary. Moving is only necessary if the signal splits and the validity of the signal (resistive or capacitive current) requires the feedback circuit.
5. Remember to disable the ground monitor's test resistor to ground before tracing a suspected fault. The low impedance of this test resistor may mask the parallel fault impedance.
6. Have a schematic of your location readily available.

Many earth/ground faults are due to water ingress. When using the BGFT, the current can dry out the fault. Additionally, if several days have passed since it has rained, the fault may have dried out on its own. To counteract the BGFT from drying out the fault, you can use a minimal current from the transmitter with a high gain setting on the receiver. If the fault disappears while using minimal current, you may have to trace the fault on several occasions, i.e., the next time it rains. Make sure you record dial settings, previous currents, and current paths to continue where you left off last time to avoid the fault drying out again while tracing.

Some Ground Fault Monitors use an earth/ground connection (reference earth/ground) to the bus and monitor the current going through that circuit to turn on/off lamps to indicate a fault on the DC bus. If you do not lift this earth/ground connection before proceeding with the BGFT connection, it may cause inadvertent operation of protection relays. Before connecting the BGFT, temporarily remove the earth/ground reference for the test duration. Once you locate the fault, simply replace the reference connection. See the application note: BGFT Working with Fault Monitors for further information.  

The output of the transmitter is 20 Hz, so it does not measure the exact current. This is not important; the value of the receiver is relative and not absolute. Just continue tracing as usual but use the new value of current for reference.     

Yes, there is an optional Mini-CT (Cat. No. 30595). You can use this for smaller connections and tight spaces.

This is due to a high impedance fault, and the unit is not generating enough current to pass through the fault. Turn the “Output voltage” switch anti-clockwise all the way, so the current output of the transmitter is at zero. Turn the 15 V/50 V switch to 50 V and proceed with the test. Caution: Always ramp up the output voltage slowly.  

You always want to find the fault with the lowest possible voltage; therefore, you must always start in the 15 V position and slowly ramp up the output voltage. See the following FAQ for when to use the 50 V setting. 

Two large alligator clamps come standard with the BGFT. The red clamp always belongs on the terminal that is associated with the earth/ground fault. If you have a positive earth/ground fault, connect the red clamp to the positive terminal of the battery bank. If you have a negative earth/ground fault, connect the red clamp to the negative terminal of the battery bank. In both cases, you should connect the black clamp (with green sticker labelling ground) to the station ground. Caution: Do NOT connect the transmitter across the plus and minus terminals of the battery string.

The battery charger may have a built-in earth/ground fault monitor, or a separate earth/ground fault monitor may be attached to the battery system. Either one will tell you if you have a negative or positive earth/ground fault.