unground

To unground a circuit or component means to sever its connection to the ground reference potential, whether that is earth ground, chassis ground, or signal ground depending on the system. In practice, this might involve removing a wire, lifting a PCB trace, opening a switch contact, or disabling a grounding strap. The effect is to leave that point electrically floating rather than held at a known voltage reference.

Ungrounding is rarely done by design in safety-critical or high-reliability work. Most modern electronics require a solid ground reference to establish voltage levels for all other nodes in the circuit. However, ungrounding occurs intentionally in some measurement and testing scenarios. A technician might unground a circuit node temporarily to take a floating voltage measurement, or to isolate a section of equipment during troubleshooting. Some industrial controllers have switchable ground connections to allow reconfiguration of signal routing between different subsystems.

Ungrounded circuits become susceptible to electrostatic buildup, induced noise from nearby power lines and radio sources, and common-mode voltage shifts. A floating analog input on a PLC or DAQ card will read erratically. Digital logic without a ground reference cannot establish logic voltage levels and will malfunction. In harsh industrial environments with heavy motors, welders, or high-frequency switching, an ungrounded point drifts rapidly and picks up coupling noise, making measurements or signals unreliable.

The term appears in service manuals and electrical schematics as an instruction for temporary modifications: 'unground pin 14 during calibration' or 'unground the shield for this measurement.' It contrasts with grounding, bonding, and earthing, though ungrounding is far less common in everyday workshop vocabulary than its opposite operations.