What indicates a sustained contact voltage when using a shunt resistor?

• A. A measured voltage of 0.0 Volts
• B. A reading of 0.1 Volts
• C. A negative voltage
• D. A Measured Voltage of 1.0 Volts or More

Answer: (D)

A sustained contact voltage is shown by a real, ongoing potential difference across the contact that can pose a shock hazard. In a setup using a shunt resistor, the voltage across the shunt equals current times the shunt resistance (V = I × R). When you measure a voltage of 1.0 volt or more, that indicates there’s a meaningful, continuous voltage present across the contact point, signaling a sustained hazard.

Very small readings like 0.0 V or 0.1 V are typically too small to indicate a sustained hazard—they can come from no current, leakage, or measurement noise. A negative voltage simply shows opposite polarity; what matters for sustained contact is the magnitude exceeding the hazard threshold, which begins at 1.0 volt or more.