Electricity + Control 2019

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ELECTRICAL PROTECTION + SAFETY

Finding good ground – electrically

In a three-phase circuit, neutral is usually shared between all three phases, with the system neutral being connected to the star point on the feeding transformer. Earthing is a critical part of electrical installations to ensure that, under fault conditions, circuit breakers will trip. Safe and le- gal installation needs to start with the selection of the right trans- former, with a star configuration to allow the connection to the neutral point. Installation by a qualified and experienced techni- cian is then ideal, to ensure optimal performance. The correct earthing or grounding of electrical currents has a number of important benefits apart from the main concern around safety. It protects equipment and appliances from surges in elec- tricity – commonly from lightning strikes or power surges – which bring dangerously high voltages of electricity into the system. Good earthing will ensure that excess electricity will go into the earth rather than damaging equipment. Enquiries: ZestWEG Group Africa,Tel: +27 (0)11 723 6000, or email: marketing@zestweg.com

According to Zest WEG Group, there are misconceptions around what constitutes ‘earth’ (or ‘ground’) and ‘neutral’ connections. Not understanding the differences can create serious problems when connections are made from on-site transformers or other power supply sources. Often this leads to earth leakage systems underperforming and compromising the safety of the equipment and operators. Johan Breytenbach, transformer sales specialist at Zest WEG Group, says that the neutral connection in an electrical installation is designed to carry current all the time, while the earth connec- tion is only supposed to carry current for a short period to trip the protection switch. “Where this is not understood and the installation is not done correctly, the trip system will not work properly. In addition, stray currents are created that can cause other problems,” he says. Experience has shown that many farmers use the neutral con- nection as the earth when they do an electrical installation. This is not correct. Current carried on a grounding conductor can result in

significant or even dangerous voltages on equipment enclosures. For this reason, the installation of ground- ing conductors and neutral conductors is carefully de- fined in electrical regulations. In alternating current (ac) electrical wiring, the earth is a conductor that provides a low impedance path to earth so that hazardous voltages do not find their way to the equipment. Under normal conditions, the earth connection does not carry any current. Neutral, on the other hand, is a circuit conductor that normally carries current back to the source. Neutral is usually connected to earth at the main electrical panel or meter, and at the final step-down transformer of the supply. Neutral is also the connec- tion point in a three-phase power supply to connect cable termination in order to gain single-phase power.

A WEG pole-mounted transformer (200kVA 11kV/400V) with the neutral and earth contact terminals visible.