I want to install LED lights in a pool. The original transformer outputs 12V 6A. Now I don't trust my life to a cheap transformer so I want to go sure. Yet I also don't want to spend more money than necessary. I don't have to live for ever.

Found an adapter that measures residual currents and breaks the circuit if delta larger 30mA. RCD safety adaptor So this sounds quite good to me.

Now I wonder, isn't it possible that in a worst case situation this device would not measure any delta between both power lines and the human between both lines beeing effectively roasted?

Found out that cheap transformers can output the full incoming current in a state of failue. Safetytransformers where a short circuit is not possible by design cost quite some money.

Is such an RCD adaptor a safeguard for any transformer failure?

Edit: Would it help to ground the poolwater - lay a cable from inside the pool to the grounding connector in the power outlet.

  • For the wondering point, yourGFCI/RCD would have to be the item that failed you as if ANY (as specified by mfr) current found its way to another drain, the RCD would trip. Anything servicing a pool must be GFCI/RCD protected. However, no one should recommend you use a product in a manner that it was not designed for. So are the LED lights intended for submersion?
    – noybman
    Aug 26, 2017 at 14:12
  • Thanks, yes the led lights are waterproof sealed in silicone. Still I suppose a pool on a tiles floor is quite good isolated from the ground so me swimming in the water would be the only resistance between both power lines....
    – AndyZ
    Aug 26, 2017 at 14:16
  • So your asking if a transformer winding failed in such a way the high and low remained isolated, but the ratio was now (essentially) 1:1?
    – noybman
    Aug 26, 2017 at 14:22
  • No, I ask if the transformer isolation failed in a way that outgoing voltage was the same as the incoming and I was sitting in 230V water not just 12V.
    – AndyZ
    Aug 26, 2017 at 14:31

1 Answer 1


Yes, it would, but 30ma won't belp you in a pool. Here's how electrocution drownings work.

  1. Current as low as 10ma stuns the person in pool.
  2. They faint.
  3. Where they fall, their nose or mouth are under water.
  4. They drown.
  5. Rescuer sees them unconscious, reaches out or jumps in to save them.
  6. Current stuns rescuer.
  7. Go to 2.

You think I jest, but often the way they know it's an electrocution drowning is multiple victims. The coroner can't tell an electrocution drowning from a normal one.

What you want is personnel-grade 8ma protection.

Another defense would be to tie your DC negative terminal to the local grounding electrode system. This means the DC is no longer an isolated system, and is a potential ground-fault path for your AC system.

  • I started to read your comment as a joke, but finished in full seriousness... I don't get it, then why is 30mA a standard for RCD breakers? Our bathroom /toilet/washing room (all the wet area) is connected via such a IΔn ≤ 30 mA 40A breaker. Now what you say sounds like that is not a real protection.
    – AndyZ
    Aug 27, 2017 at 7:53
  • As I cannot find any reasonably priced personal-grade RCD protector below 10mA, would you suggest to go for the safety transformer where a short circuit is disabled by design?
    – AndyZ
    Aug 27, 2017 at 7:59
  • Do I understand it correctly, that with a 10mA fail current and wiring the negative pole to the grounding would still not trigger the 30mA, but would direct the 10mA to ground as this would be the way of least resistance?
    – AndyZ
    Aug 27, 2017 at 8:49
  • Found an interesing diagram showing that at 10mA muscle control is lost after around 10 seconds according to the IEC 64 standard. So a 10mA RCD with 20ms reaction time should be good enough. Yet the minus pole of the transformer must be grounded for this to trigger.
    – AndyZ
    Aug 27, 2017 at 9:10

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