Nonsense.
30mA can easily kill. Whether a current is lethal or not depends on a number of factors including the age, health and gender of the person, the path the current takes and how long it lasts for.
30mA was chosen as a trip point for RCDs because it's highly unlikely a short term exposure would result in any harm. It's also a balance between being safe and nuisance tripping.
In electrical installations, there are 2 kinds of RCD's, one of 300mA in the mains input intended for protection against risk of fire by leak current, and one or more 30mA RCD's for protection against risks of electrocution.
And you say this is not safe ?
30 mA has been choosen to be a safe limit with no risk of fibrillation. It has never been choosen as a balance between safe and nuisance tripping, but only for safety.
Not every circuit most be protected with 30 mA RCD's, washing machine and dishwasher for exemple are only protected by 300 mA RCD's.
Such a current of only 30mA is also not high enough to produce lethal burn injuries.
I agree that in case of using a pacemaker, 30 mA can be dangerous, but this is an exception.
You must also be aware that very high currents greater than 500 mA does generally not induce fibrillation: that's the reason why electric chair does not always kill at once.
Tap water is not de-ionised and its conductivity varies with voltage, as with most non-metals. This was mentioned in the video, if you care to watch.
Conductivity of tap water vary with temperature, but not with voltage. Of course with dc current, you have another behaviour because you have electrolyse of water, but this does not happen with ac current.
It is a nonsense to say that conductivity of most non-metals vary with voltage. Carbon resistors for exemple does not vary of value with voltage. Only with temperature.
The guy of the video does not know what he is speaking about.
In this case, the most common failure mode may be off but switch can and do fail in the closed position and in a humid environment such as a shower head this is more likely than where it's dry.
The only ways this could happen are:
- welded contacts: this does not happen because current is limited by the resistance. There are also 2 contacts in serie for greater safety.
- broken spring: manufacturers are using inox springs to avoid corrosion failure of springs.
Thermal fuse can't be used because current is as high as 50A in a 110V shower and there is no way to place it reliabily in contact with the resistance. In normal working, this resistance is far hotter than water.
If the shower is working without water, the resistance became at once so hot that it melt and break.