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

I've seen both options where the manufacturer recommends the mains power is removed (from the pump or the SELV transformer) whilst people are using the pool.

We've used both types at home, and always followed the course of action that the mains plug is removed when people are in the pool.

Interestingly, I spoke to a chinese pump manufacturer directly and they recommended a 12V AC pump as being safe for swimming pools (they sell both 240V AC, 12v AC, 12 & 24V DC pumps, so theoretically aren't biased. Their reseller in the EU however, still has the instructions "switch off before getting in the water". How is it possible for companies such as Bestway to be selling a waterfall / fountain style attachment for splasher pools that is clearly for use while in the pool (see marketing photos) if there are no pumps available that anyone will say are safe to use with them?

Thank you for taking the time to respond. Not quite what I hoped for but reassured that I'm not the only one concerned about the safety.

Worth also noting that:

1. There is no voltage considered "safe" when someone is fully immersed in water.
   
   
2. In Sections 701 and 702, BS 7671:2018+A2:2022 limits the types of electronic equipment that can be used as a source for SELV/PELV in certain zones.

Thank you for pointing me to that section. 702.410.3.4.1 does at the end state "The socket outlet of a circuit supplying such equipment and the control device of such equipment shall have a notice in order to warn the user that this equipment shall be used only when the swimming pool is not occupied by persons".... which is great (and effectively explains why all the pump manuals state "this product must not be used while water is occupied", but public swimming baths / water splash parks etc have pumps running while occupied, so there must be more to it than what is contained with the "requirements for electrical installation". Is there a separate british standard used for commercial pools / water parks (fountains in an enclosed space children run around in and under)?

Many thanks.

note that in a full size swimming pool the pump is not submersible, but connected to the larger pool by a considerable length of pipe. The resistance of the water and the length to cross-section ratio means that in effect the water enters and leaves the pool in a way that there is no dangerous potential difference in the water. Similarly pool lights are firstly ELV and secondly enclosed in such a way that the light enters the water through a window from a sealed box with a light in it. Again, even if that box fills with water, and it is not really supposed to, the ability to induce a significant difference in voltage between any two points in the pool is very much limited.

Standards aside, a system where the voltage is in the water is lower, is likely to be safer, unless the construction quality in the lower voltage model is poorer as a consequence. However, as Graham notes the wet human  is a lot more vulnerable than a  dry one, and apparently innocent things like metal steps introducing a near earth voltage can become a hazard  during a fault if current paths have not carefully considered and eliminated. (simple measures like decking or plastic steps can raise the impedance of the fault loop to external ground)

However if the automatic disconnection in the form or RCD etc is working as intended, the risk is moderate, as you have to be in the water when the pump is on,  and in a place in the water where there is a significant voltage gradient, at the very moment  when a fault occurs. I'm sure plenty of folk ignore or forget the advice to unplug and live to swim another day, but the risk is not truly zero.

Mike.

edit PS
you might find this discussion of hand held electrode type baby bath heaters interesting - some of the thoughts are the same.

electrode type baby bath heater

It is amazing the difference between CE and safety mark parts of the world, and the rest.

I think that a commercial pump in a public swimming pool will be an entirely different beast to that which you'd be prepared to have on your domestic setup.

For example, it would probably live in a plantroom, it could be a mechanical pump driven my a separate electric motor. If the mechanical coupling of the two is made of an insulating material & they are mounted on a non-conductive bed it would be pretty much impossible for a fault in the motor to transfer to the water. 

The RCD and AC 240v option however, has an earth at the motor, so theoretically, a failure will cause an earth fault and trip the RCD, but, if for some design reason, the earth isn't affected by the mechanical fault and water gets to the live, the pool is then electrified to 240v and then RCD does not trip. Typically, this is accounted for by bonding the pool water to the earth, though it's not as I understand it so trivial, since if you do that, you expose the water to potential fluctuations in the earth voltage (TNCS supply). To avoid that, you'd then convert the supply to TT setup.

"Bonding" (or Earthing) water isn't simple. The basic issue is that relatively clean fresh water has considerable resistance - even a few cm of 15mm plastic pipe can easily come in at several tens of kΩ. The size of the pool might in effect give a much larger c.s.a. and hence lower resistances, but often the contact area - either to the bond, or to the fault - is limited - which tends to mean that there's a considerable resistance that can't be avoided. Even at 230V, 7.67kΩ would be enough to mean a 30mA RCD wouldn't reliably trip.

Then there's some fundaments of ADS to worry about - the usual disconnection times are only expected to protect around 95% of the population under normal dry conditions - the remaining 5% may have lower body resistances and so be more vulnerable to a given voltage for a given duration. Immersed in water, probably a lot more of us would fall into that category. RCDs are usually faster than minimum requirements - but not necessarily that much faster under all circumstances, even when working to specification. Then there's the issue of RCD reliability - a number of studies suggest that around 7% RCDs in service are faulty (either fail to trip at all or don't trip within the specified time).

As Mike suggests, the water resistance effect can be used to advantage though - e.g. put the pump in a separate container away from the main body of the pool, connect it using relatively long and thin insulating tubing, and the water resistance then helps rather than hinders (both in terms of voltages from local faults and any PME earthing).

   - Andy.

I wired a couple of pumps for a public swimming pool, not that many years ago.

The pumps were standard types close coupled to induction motors, as would be used for chilled water or wet central heating in large buildings.

The pumps were some distance away from the pool, and the pipes were plastic, presumably the length of plastic pipe was considered a sufficient precaution.

I did not design the installation, but was simply connecting pumps installed by others. Two duty/standby pairs of pumps. One pair for a waterfall and the other pair for a waterslide. 

The heat from two large air conditioning chillers was rejected into the swimming pool thereby warming the water. This worked well except in heatwave conditions when the pool became too warm. I suggested that in such conditions that the waterfall pumps be run at night in order to cool the water.

The conductivity of a municipal swimming pool water is monitored and reported in units of 'total dissolved solids' although the exact choice of "action limit" when the water needs changing or filter need cleaning depends on things like chlorination levels. 

Typically a TDS level of a few thousand PPM for a swimming pool. (some hundreds of ohms on a cm cube ) Compared to a few hundred for tap water (some k ohms per cm cube.).

Converting to a single % 'TDS' total dissolved solids from measuring conductivity is a bit of a con, as the different ions do not have quite the same mobility in a given electric field, but close enough for some generalizations to within a factor of 2. That may sound terrible, but as the salt concentration varies by factors of ten and is about as uniform as wind-speed in places where water flows and mixes, it is often good enough.

(1uS/cm is 1 megohm.cm and 100uS/cm is 10k.cm 1000uS.cm 1k ohm.cm)

These are American figures, and their idea of clean tap water is not the same as ours, but it is quite similar.

In the table  below "442 solution" contain the following salts diluted in pure water: 40% sodium bicarbonate, 40% sodium sulphate and 20% sodium chloride. These represent the main conductive ions that are in typical surface and ground water. A purely sodium chloride solution is probably more representative of brackish salt marshes or sea water.

Note the dramatic effect of seawater -  less than 20 ohms across a 1cm cube compared to k ohms.

Mike

PS

At the other extreme I have worked on an RF power  system where cooling water was pumped over an anode at 10kV DC off ground, and 28kV p-p of RF superimposed, isolated by a few feet of what was in effect rather expensive garden hose. That rather scary system also monitored conductivity and shut itself off at 1 megohm cm or so, and had an ion exchange resin filtering a percentage of the main flow, so that the low conductivity was maintained. (well you had to run the pumps for 15 mins until it would even allow you to switch the HV on ;-)  )