I have an anti-static mat that comes with a plug that only has a ground lead. Out of curiosity, I measured the voltages between the live, neutral, ground, and my radiator.
As expected, there is 240VAC between live and neutral, and in my case there is no AC voltage between neutral and ground. However, I measure 1VAC and 20mV DC between ground and my radiator.
I understand that there might be a difference between neutral and ground due to wire resistance and large return currents on the neutral wire. What I don't understand is where the potential difference between ground and my radiator comes from. It is my understanding that any ground current would trip the RCD.
As a follow-up question: What is the better location to connect my anti-static mat? I would prefer to not expose myself to random voltages, even though I understand it should not matter too much as long as I'm not grounding myself to two different potentials.