Which is safer/safest pump style in a garden 'splasher style' swimming pool?

SELV (especially 12V a.c. or 30V d.c. or below) has a lot to recommend it. In normal operation it's completely isolated. Under single fault conditions (as it's separated - SELV rather than PELV) no shock current can flow as the fault merely references the system to the local (earth) potential at the point of the fault. Even if you had two different faults on opposite poles, they'd have to be widely spaced to be able to put a current through a human body, and even then the currents involved (due to the low voltage and resistance of the water) are likely to be tiny.

Nothing's 100%, but it's a pretty good bet.

   - Andy.

Thanks Andy. So if I understand you correctly, even if I were to run a 24V DC motor drawing 100W on say a 120W transformer, then although there would be maximum potential 5A current available at 24V travelling through the water (assuming no fault in the insulation between windings within the transformer), then the voltage would be around 12v between the positive and negative wire (about halved), the current would be substantially reduced by the resistance of the water, even if you managed to get your finger inside the pump housing to be close to the wires. At a distance of circa 2m of plastic 32mm pipe, the main body of pool water would be at a substantially lower max current and voltage, even though with no RCD on the SELV side it would be uninterrupted, this shouldn't be dangerous so as to cause tingle even (guessing now, I've not done the sums based on water resistance yet) - which I guess then would make me ponder - would it be possible for there to be an undetected fault in the SELV pump motor, submerged or otherwise that might permit the motor still to run seemingly normally while electrifying the water?

This scenario is far outside the physics I studied at school, but I think I have a grasp of the concept at least. I've expanded my knowledge by buying the "Requirements for electrical installations" and other similar texts, but, my formal education in this area is to school A-Level physics, which focussed more on functionality of electrical windings and such like than safety to this level.

I'm looking to ensure for certain that one cannot get close to remotely like 30 milli amps of shock (RCD rating), even at 24v, and this will be a factor of 10 times less dangerous (ok, electical danger isn't linear like that), than a 240v with earth bonding etc.

Would PELV in a TT system be even safer than SELV though on the basis that an RCD would potentially cut the circuit removing any current in the event of fault, however small - this feels true, though PELV is considered less safe than SELV because of the link to the supply side (presumably because that's easier to say than "SELV is safest with any circuit other than TT").  Am I missing something obvious here, or am I correct that the electrical wiring regs have been written with simplicity in mind in this scenario?

Thanks Andy. So if I understand you correctly, even if I were to run a 24V DC motor drawing 100W on say a 120W transformer, then although there would be maximum potential 5A current available at 24V travelling through the water (assuming no fault in the insulation between windings within the transformer), then the voltage would be around 12v between the positive and negative wire (about halved), the current would be substantially reduced by the resistance of the water, even if you managed to get your finger inside the pump housing to be close to the wires. At a distance of circa 2m of plastic 32mm pipe, the main body of pool water would be at a substantially lower max current and voltage, even though with no RCD on the SELV side it would be uninterrupted, this shouldn't be dangerous so as to cause tingle even (guessing now, I've not done the sums based on water resistance yet) - which I guess then would make me ponder - would it be possible for there to be an undetected fault in the SELV pump motor, submerged or otherwise that might permit the motor still to run seemingly normally while electrifying the water?

This scenario is far outside the physics I studied at school, but I think I have a grasp of the concept at least. I've expanded my knowledge by buying the "Requirements for electrical installations" and other similar texts, but, my formal education in this area is to school A-Level physics, which focussed more on functionality of electrical windings and such like than safety to this level.

I'm looking to ensure for certain that one cannot get close to remotely like 30 milli amps of shock (RCD rating), even at 24v, and this will be a factor of 10 times less dangerous (ok, electical danger isn't linear like that), than a 240v with earth bonding etc.

Would PELV in a TT system be even safer than SELV though on the basis that an RCD would potentially cut the circuit removing any current in the event of fault, however small - this feels true, though PELV is considered less safe than SELV because of the link to the supply side (presumably because that's easier to say than "SELV is safest with any circuit other than TT").  Am I missing something obvious here, or am I correct that the electrical wiring regs have been written with simplicity in mind in this scenario?

Would PELV in a TT system be even safer than SELV though on the basis that an RCD would potentially cut the circuit removing any current in the event of fault, however small - this feels true, though PELV is considered less safe than SELV because of the link to the supply side (presumably because that's easier to say than "SELV is safest with any circuit other than TT").  Am I missing something obvious here, or am I correct that the electrical wiring regs have been written with simplicity in mind in this scenario?

It rather depends what earth reference you use for the PELV, and if it is at the same voltage as anything else in or near the water or another not quite earth some volts offset. This is not as easy to be sure of as ensuring  ' fully isolated' - shavers sockets have the same problem, so SELV is often safer.

The key to shock reduction is clean non salty water, and low enough voltages not to get dangerous currents through the essential parts of the human. Swimming in HV transformer oil is probably off limits for other reasons, but electrically would be one solution.

And yup,  the regs have to say something better than 'think it out case by case' but the general guidance is just that - general - and there will always be some corner cases where the regs book answer is not the best.

Mike.