People Shocked in U.S. Swimming Pool.

A common occurrence in the US, even such incidents as Caddyshack and Bill Murray.


Jaymack.

https://www.google.com/search?q=Caddyshack+No+big+deal&oq=Caddyshack+No+big+deal&aqs=chrome..69i57j0.21364j0j4&sourceid=chrome&ie=UTF-8

The Umercans have form for this - they succeeded in killing quite a few of their soldiers on bases in hot and dusty places based on a gross lack of understanding of earthing and bonding arrangements that might have been sensible to observe in shower blocks - way to go KBR


There are lots of them however, so loosing a few is probably considered fairly unimportant


OMS

The fatal current doesn't circulate in the middle of the swimming pool. You need to be at the edge, preferably grabbing on to a metal hand rail or similar.

Interestingly the Americans have also managed to kill people swimming in rivers/marinas/lakes due to connecting their boats to a shore supply and getting circulating currents (https://www.boatus.com/seaworthy/magazine/2013/july/electric-shock-drowning-explained.asp), mainly children, and even avoiding the need to grab an earthed rail if the voltage gradient in the water is sufficient. It may also be enough in a swimming pool. Note that the lack of RCDs in the supply systems (a requirement in the UK for supplies to small vessels as far as I am aware) is a major reason for such faults being undetected until it is too late.

Alasdair

Chris Pearson:

So if you are in the middle of a swimming pool, how does a fatal current circulate?

 

The yanks like to think of it as plasma in the water, there is a voltage gradient between the body and source of voltage. Similar to corona discharge in the air at HV.   


Jaymack

If there is current flow in the water between any 2 points, then although the bulk of the current flows the short path, though there is a voltage gradient across all space because of this
click here for pic

All points on any one red line are at the same voltage.  Their spacing is the field strength in volts/meter.

Far enough away the voltage contours get far enough apart (volts per meter gradient low enough) not to trouble the scorers, but it is still there. The field at a distance is in proportion to the initial voltage difference times the spacing of the 2 electrodes.


Generally people are less conductive than salt water ,and more conductive than fresh. 


If you are the high resistance element, you do not want to be in series with a body of conducting water - swimming as it were in between the capacitor plates and  finding most of the volts dropped across you .

If you are the low resistance element then being near one electrode is bad as current that would have flowed in the water around you tends to take the easier path.

In either case you are stuffed if the current is high enough, but the voltage contours look quite different, either bunching towards the body or moving as if trying to avoid it, and it varies if you would stand a better chance moving to be either parallel to or at right angles to the direction of the current flow.



The real secret to an event free life is only to permit 12V transformer isolated lighting for under water illumination that is not  via an air gapped window, and to feed mains to moored boats from individually TT supplies and RCDs.

And in general under water mains voltage lights are just a bad thing in a swimming pool, even if your local rules permit them

and to feed mains to moored boats from individually TT supplies and RCDs.

I suspect part of the problem is that the American' just don't do TT - I think that in most cirumstances their regs simply prohibit it. They go for a multiply earthed neutral (PME-ish) approach instead - often directly connected to the HV neutral/earth- which while it gives a low impedance to earth in normal conditions, can come horribly unstuck under what we'd call broken PEN conditions.

   - Andy.

The real problem is not the TT or not but the fact that most ships/boats are IT so an earth fault doesn't manifest itself until there is a fault on the/an other phase/pole. There is normally an earth connection to the propeller shaft or engine which when connecting to a shore supply is connected to earth and will cause a trip if there is an earth fault on the vessel, provided the earth conductor is intact. If you read the article I provided a link to they say that the problems have been where there is an earth fault and the earth conductor in the connection (or ground conductor, being Yanks) is broken then the return path is through the water. I think the biggest problems have been with people swimming near the boat propellers (you normally board a moored/anchored boat via steps at the stern) where the voltage gradient is greatest. As the problem is a broken earth connection I think it is probably irrelevant what the earthing scheme on shore is, though no doubt someone will correct me.

Alasdair

Chris Pearson:

OMS:

There are lots of them however, so loosing a few is probably considered fairly unimportant

"GIs"!


So if you are in the middle of a swimming pool, how does a fatal current circulate?

 

Above ground pool basin, no provision for lightning protection and a hot, arid location prone to lightning incidents would be one example I can think of


Regards


OMS