This could occur by a major fault, resulting in the ground wire sharing the load current with the neutral wire, or supplying the total return. It should be pointed out, that this current becomes the chassis leakage current for conductive enclosure when tested under open ground condition as discussed below. Such leakage can be both capacitive across a dielectric, and resistive, through conductive flux residue or poor insulation. Line filters installed to protect against conductive EMI, particular in newer computerized devices. Switching power supplies with significant electronics directly connected to the power line and complicated by the introduction of the higher switching frequencies used in the supply.
Leakage current is dependent upon wire gage, insulation dielectric and length.
Open neutral will usually represent the worst case. Block schematic of a line operated instrument with isolated circuits. As stated above, this current under the condition of an open ground is the same as the earth current. With ground intact, the current should be very low, reflecting the miiliohm impedance of the ground wire paralleling the 1000 ohm AAMI load. Differentiation is made between Earth and Chassis current due to the wide use of insulated enclosures today, and thus no accessibility to conductive chassis.