Difference between AC and DC current

[GENIERE]

I think he means that if an appliance is turned on, it acts as a resistor connected to the hot power line and so can deliver an electric shock. Likewise, if an appliance is plugged in and turned on, the 'neutral' (U.S.'return') is 'hot' too, if not properly grounded or some distance from ground. So if you put a knife in an English (240v) toaster and and grab the radiator with your other hand, zap.

The US National Electrical Code requires that the neutral conductor be grounded at the service entrance (residential use). It is NOT hot with respect to Earth except for the small voltage drop across it due to its impedance. This is UNIVERSALLY true regardless of which country you reside in; a current carrying conductor will never be at the same potential as the safety-grounding conductor if it is carrying current except at the bonding point.

There are specific circumstances where it is necessary to isolate the system from ground as in operating suites, gas stations, grain silos; anyplace where a spark to ground my ignite an explosive atmosphere i.e., anesthetics, gasoline fumes, grain dust. This is usually accomplished by using an isolation transformer whose secondary windings produce the desired voltage(s) and are maintained to assure both current carrying conductors have at least 1megohm of impedance to ground. The floor of the operating suite must be conductive to ground (forget the maximum impedance) to dissipate static charges. You can, I have done so, grasp one of the conductors in an operating suite (one that uses explosive anethetics) and intentionally Earth one’s self. There are micro amps of current flow through the body but no perceptual shock. Yes I do know that micro amps may cause cardiac fibrillation but why that does NOT happen is a function of current density, not total current flow.

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