Effect of someone touching a device that is protectively earthed

[stickinsect]

I am trying to calculate (as a theoretical exercise) what the effect would be if someone touched an electrical device that is protectively earthed. I would really appreciate it if anyone could verify my workings.

I am assuming that the current flowing into the enclosure of the class 1 device is 1 Amp (could this happen?), the earth resistance from that point of the enclosure to ground is 0.2 Ohms and the body resistance (to ground) of the person touching the device is 1,000 Ohms.

If the device earth resistance and the body resistance are treated as being in parallel, the total resistance would be 0.19996 Ohms (1/Rtotal = 1/Rdevice + 1/1body).

The voltage drop across the device would be 0.19996 V (0.19996 Ohms * 1 Amp).

The current flowing through the person would therefore be 0.00019996 Amps (0.19996 V / 1000 Ohms). This would likely be below the threshold of perception.

Does this look reasonable?

 

[brianmoooore]

Less than putting your fingers across the ends of an exhausted AA battery, so way below being perceptible by touching with your hands..
May be able to detect such a low voltage with your tongue.

 

[littlespark]

a fresh 9V battery (old smoke alarm type) can be detected with your tongue..

dont ask how i know

 

[ELECNEWT]

I am trying to calculate (as a theoretical exercise) what the effect would be if someone touched an electrical device that is protectively earthed. I would really appreciate it if anyone could verify my workings.

I am assuming that the current flowing into the enclosure of the class 1 device is 1 Amp (could this happen?), the earth resistance from that point of the enclosure to ground is 0.2 Ohms and the body resistance (to ground) of the person touching the device is 1,000 Ohms.

If the device earth resistance and the body resistance are treated as being in parallel, the total resistance would be 0.19996 Ohms (1/Rtotal = 1/Rdevice + 1/1body).

The voltage drop across the device would be 0.19996 V (0.19996 Ohms * 1 Amp).

The current flowing through the person would therefore be 0.00019996 Amps (0.19996 V / 1000 Ohms). This would likely be below the threshold of perception.

Does this look reasonable?

See attached PDF