Where do these hidden/parasitic paths matter?

Consider coupling from YOU to the concrete under the floor: 1cm spacing, area of 0.1meter by 0.4 meter, dielectric constant---use that of air (1.000002 or close).

What is the capacitance from you to the floor? $$Capacitance = Eo * Er * Area/distance$$ or [9e-12Farad/meter * 1] * [0.1 * 0.4] / 0.01 = 9e-12 * 0.04/0.01 Capacitance = 9e-12 * = 36 picoFarad.

So? Now touch a neon-sign transformer, 50,000 volts at 60Hz (377 radian/second). The dV/dT = 50,000 (assumed peak) * d(sin(60Hz)/dT) = 50,000 * 377 ~~~ 20Million volts per second.

What is the current through you? I = C * dV/dt = 36 e-12 * 20e+6 = 700 microAmps.

You want to avoid that. Even if there is no obviously closed circuit.

Where do these hidden/parasitic paths matter?

Consider coupling from YOU to the concrete under the floor: 1cm spacing, area of 0.1meter by 0.3 meter, dielectric constant---use that of air (1.000002 or close).

What is the capacitance from you to the floor? $$Capacitance = Eo * Er * Area/distance$$ or [9e-12Farad/meter * 1] * [0.1 * 0.3] / 0.01 = 9e-12 * 0.03/0.01 Capacitance = 9e-12 * 3 = 36 picoFarad.

So? Now touch a neon-sign transformer, 50,000 volts at 60Hz (377 radian/second). The dV/dT = 50,000 (assumed peak) * d(sin(60Hz)/dT) = 50,000 * 377 ~~~ 20Million volts per second.

What is the current through you? I = C * dV/dt = 36 e-12 * 20e+6 = 700 microAmps.

You want to avoid that. Even if there is no obviously closed circuit.