Chris Pearson: 
 

gkenyon: 
There is NO ‘residual current’. The OCPD will operate, but it is likely the person in the bath will be seriously injured or killed before that happens, as the electricity tracks through salt straight to the person's trunk, as it's the most conductive thing in the water, to get from Line to Neutral.

As I said, no protective conductor, no alternative path other than L-N, so an RCD is wholly ineffective. This is not a theory … it was proven in an investigation after two children died in a bath in Germany after a shaver on charge from the mains fell into the water and killed them both.

I am struggling with this. We have in the bath water a couple of electrodes. The bather is in contact with neither of them. How can the bather be a lower resistance between them than the bath water?

Electricity does not flow in ionic solutions in exactly the same way it does in solid conductors. 

AS mapj1 pointed out also, there are voltage gradients … but it is slightly more complicated than that. The presence of the body distorts the electric field in various ways, some to do with “salt” (ion) concentrations. 

Add to that, that the body resistance is lowered, and there are a lot of pathways for the current to enter the body - it's not simply hand-to-feet or hand-to-hand shock.

Finally, it may not be ventricular fibrillation that kills someone, but drowning due to muscle spasms and lack of control. 

IN fact, limitation of voltage in immersed situations is not a guarantee of protection against electric shock - a few volts is all it takes. IEC TR 60947-5 recommends that, whatever the operating voltage, current limiting (at a very few mA - strong muscular reactions occur at as little as 5 mA) is the only feasible option for equipment intended for use where people are immersed in water.

Chris Pearson: 
 

gkenyon: 
There is NO ‘residual current’. The OCPD will operate, but it is likely the person in the bath will be seriously injured or killed before that happens, as the electricity tracks through salt straight to the person's trunk, as it's the most conductive thing in the water, to get from Line to Neutral.

As I said, no protective conductor, no alternative path other than L-N, so an RCD is wholly ineffective. This is not a theory … it was proven in an investigation after two children died in a bath in Germany after a shaver on charge from the mains fell into the water and killed them both.

I am struggling with this. We have in the bath water a couple of electrodes. The bather is in contact with neither of them. How can the bather be a lower resistance between them than the bath water?

Electricity does not flow in ionic solutions in exactly the same way it does in solid conductors. 

AS mapj1 pointed out also, there are voltage gradients … but it is slightly more complicated than that. The presence of the body distorts the electric field in various ways, some to do with “salt” (ion) concentrations. 

Add to that, that the body resistance is lowered, and there are a lot of pathways for the current to enter the body - it's not simply hand-to-feet or hand-to-hand shock.

Finally, it may not be ventricular fibrillation that kills someone, but drowning due to muscle spasms and lack of control. 

IN fact, limitation of voltage in immersed situations is not a guarantee of protection against electric shock - a few volts is all it takes. IEC TR 60947-5 recommends that, whatever the operating voltage, current limiting (at a very few mA - strong muscular reactions occur at as little as 5 mA) is the only feasible option for equipment intended for use where people are immersed in water.