A disconnect means must be provided on the supply side of all fuses in circuits with a voltage of at least what voltage to ground?

A disconnect means is necessary on the supply side of all fuses in circuits where the voltage to ground is at least 150 volts. This requirement is fundamentally rooted in safety, ensuring that maintenance personnel can safely disconnect power without risk of electrical shock or equipment damage. In systems with voltages of 150 volts or higher, the potential risk of electric shock increases significantly, thereby necessitating a mandated disconnect to allow safe maintenance or inspections.

By requiring a disconnect means at this voltage level, codes and standards aim to enhance safety practices in electrical installations, ensuring clear and accessible points to safely isolate electrical circuits. Lower voltage levels, such as those below 150 volts, typically involve less risk and, therefore, do not surpass the safety thresholds that would require such a measure.