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Why do I need to earth that, when it is in the ground?

Over the past four to five months, we at NECA along with our good friends at ESV have been carrying out AS/NZS 3000 seminars around the states.

Part of the presentation included the new requirements to earth all conductive parts within arms reach (AS/NZS 3000, part 1 section 11.4.12 (definition)) of a swimming pool or spa, regardless of the type of motor pump type being installed. In the current wiring rules, this requirements only applies to class 1 electrical equipment i.e. electrical equipment that is not double or reinforced insulated.

Many attending electricians have raised the question, “why do I need to earth a metallic fence that is installed buried in the earth (ground)?” Is it not earthed by the fact it is buried partially in the earth (ground)?

The answer is not a simple one, but quite logical when correctly explained. So here I go having a shot at explaining the dangers of having exposed conductive parts within arms reach of a pool or spa.

Firstly, we need to understand where the voltage originates from. With swimming pools or spas it is the water that raises to a voltage (Potential). Over the years I have measured voltages ranging from 5V to 40Volts in the water, when measured with a volt meter connected to an independent earth spike pushed into the general mass of earth (ground).

The voltage occurs in the water usually from one of two sources. Firstly, the electrical circulating pump motor breaks down and a voltage happens on the steel shaft of the motor and the steel pump casing, thus energising the water to a given voltage. This short circuit of the electrical system causes the protection equipment to operate quickly, due to the mandatory requirements to have Residential Current Devices (RCD) fitted to the electrical circuit supplying electrical equipment associated with swimming pools and spas.

The other source is more complicated and is the most common scenario for persons receiving electric shocks, with in swimming pools and spas. This is the main reason for introducing the new mandatory requirement to bond all metallic parts with in arms reach of the swimming pool or spa water.

Voltage rise of the water is usually introduced into the water via the earthed metal parts of the swimming pool or spa ancillary equipment. Items such as the metallic water circulating pump, gas fired electronically controlled water heaters, or any other electrical equipment that is of Class 1 construction (requires Earthing).

The earthing arrangement of every electrical installation has a voltage (potential) with reference to the general mass of earth. However, the value is usually less than 5V and has no significant effect on the electrical installation or persons within the electrical installation.

For support, guidance or further specific information, contact NECA Technical Manager, Roy Sand on 1300300031.

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