A ground detection voltmeter is used to monitor a floating battery bank for inadvertent grounding of either side. Historically, a center zero analog meter has been used for this application. The meter typically has a 500uA or 1mA DC movement, with a voltage scale of 100-0-100 for a 72V battery bank, 150-0-150 for a 125V battery bank or 300-0-300 for a 250V battery bank. Two high value resistors are installed across the battery and the center tap connected to the grounded meter. A low impedance to ground on either side of the battery causes the meter to move off center, indicating both the severity of the fault and which side it is on. The resistor value is selected so that a direct short to ground reads the full voltage.

A digital bargraph meter will easily replace the analog meter in this circuit, often mounting in the same panel cutout.  The bargraph meter provides both a digital readout and a highly visible bar to indicate a fault situation.  To help spot a problem more quickly, a tricolor bar can be configured to change color when a threshold level is exceeded in either direction. The bargraph meter offers several other improvements over the analog meter.  It may include relay outputs to activate a service alert or alarm at specific fault levels. It may also have a digital interface for remote monitoring through a network or SCADA system. 

BarGraphs & Displays

Weschler Instruments