Electrics/Transformer Safety Basics

Thread Starter


Joined Nov 2, 2008
Are my assumptions correct?

'-' means touching.

Mains L - Human body - GND/Earth = SHOCK

Mains N - Human body - GND/Earth = "SAFE"

Mains L/N - Transformer - Human body - GND/Earth = "SAFE"

Mains L/N - Transformer - Human across transformer - GND/Earth = SHOCK

Mains L/N - Transformer - Oscilloscope GND Probe = DAMAGE/SHOCK

Mains L/N - Transformer - Oscilloscope (connected to mains via isolating transformer) GND Probe = "NO DAMAGE/SAFE"

Mains L/N - Transformer - Mains Tester/Screwdriver = NO MAINS INDICATION/NEON OFF



Joined Nov 9, 2007
You are correct

The neutral is rarely at earth potential in any installation. It is quite possible to get a belt from the neutral, especially in older installations.

#3 to #7
I am not sure what you mean by 'transformer' are you referring to the body (core) or terminals?

In #3 for instance if the body of the transformer is grounded and a live line lead touches the body this should cause a fuse or breaker to blow. So the transformer body would then be unharmful to touch. It is hoped that the fuse would be quick enough to protect if the human was touching before the live lead.

Thread Starter


Joined Nov 2, 2008
Thanks for replying.

#3 to #7 Im referring to the touching of the secondary winding/terminal of the transformer.

The transformer would be an isolating transformer or where the transformer body will not be grounded.

#6 and #7 Im most unsure with.:confused: