Imported: Outdoor pool Problem

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DougP
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Imported: Outdoor pool Problem

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Lin13
Nov 26 2015 12:25


I have a situation where a new pool has been installed with the usual circulating pump and chlorinator system.
The submain from the house switchboard is fed into a small sub board in the pool house via an RCD and then to a power point for the chlorinator. The circ. pump then is plugged into the output from the chlorinator unit.
I have checked the input and output cables from the power point right thru to the pump motor all correct.
All metal parts have been earthed back to the earth bar.
Tests after installation showed a line loop test at the pump / chlorinator unit power point of 0.52ohms.
The customer complained that they were getting tingling shocks when exiting the pool on to the paved surround.
Placing a probe in the water and 1 on the paving area / a probe in the ground next to the pool found an AC voltage of 1.25V and a DC voltage of 3.75V
Adding an earth wire directly connected to the earth bar reduced this voltage to Zero.
The pump and motor unit is metal which is earthed with all the pipe work in plastic.
My question is has anyone had this situation before, am I missing something or do I need to basically connect the pool water to earth ?


mf51to1
Nov 26 2015 14:35


Have you earth tested to some reinforced steel inside the concrete slab around the pool? Sometimes you will need to break away some concrete to do this.

AlecK
Nov 26 2015 15:25


What is the pool made of?

Lin13
Nov 26 2015 15:48


Thanks for replies.
Exposing some steel reinforcing was my next step so I will do that tomorrow.

Lin13
Nov 26 2015 15:49


The pool is fibre glass

AlecK
Nov 26 2015 17:25


OK so you\'ve earthed the socket; presumably C-curve protection at 16 or 20 A, so 0.52 s plenty low enough.

But have you done equipotential bonding?

The pool structure itself is non-conductive o 5.6.2.6.3 dos not apply.
But still required to bond electrical equipment [5.6.2.6.1] ; Note that the pump and possibly the chlorinator will be in contact with pool water even if they are outside all Zones. If such items don\'t have double insulation internally - and many pumps don\'t - they need to be bonded (as well as being earthed). And if any of this needs to be bonded, then any conductive fixtures and fittings& also need to be bonded[5.6.2.6.2].

I suspect that this is at least part of your problem, and the fibreglass (insulating) body of the pool means the pool water can be at a different potential from the paving on the ground next to it.
Especially likely when the earthing system is from equipment via socket to DB then back to MSB, so the electrode will be some distance away.

It\'s not uncommon for ground to be \"live\" with reference to the earthing system. For example, neighbour\'s faulty neutral will mean return current flowing though the ground to wherever it can find a way \"home\".
Ground isn\'t highly conductive so there wil be a voltage gradient.
That\'s why we do equipotential bonding.

mf51to1
Dec 08 2015 21:18


What did you find lin?

pluto
Dec 08 2015 21:52


How do you measure the voltage? If a digital Meter, place a 2000 ohm resistor across the measuring leads when measuring the voltage.

With 2000 ohms load you will be lucky to meansure any voltage as a digital meter will only measuring very small leakage currents which are not practical to eliminate with the MEN system as used in New Zealand.

Lin13
Dec 10 2015 19:58


The only metalwork was the circ.pump which was bonded.
Was difficult to access the reinforcing in the concrete pool surround as it was done before I was on site.
I put a probe in the ground and measured the difference between that and the earth bar at the switchboard was 1.5K ohms.
I installed an earth rod in the ground by the pool and connected it to the earth bar.
There is approx. 20 metres between the main house earth rod and the pool and the ground is quite dry.
Now the problem has gone.
Thanks everyone for help I think it shows that the steel reinforcing in the concrete surround should have had a connection point for an earth connection not something always considered by concrete installers.
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