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This is where a condition exists caused by power system fault current to earth at a High Voltage installation (ie: HV transformer, HV pole) have it's conductor touching earth. The electrical potential of the surrounding ground rises due to the fault current to earth via the impedance of the earthing system of the installation.




This fault could be hazardous to a person in the EPR zone (see diagram below) who maybe touching a wire connected to the earthing system not very far away, such as a telephone line that is earth back through that exchange.

This fault may only last a very short time (less than 2 seconds) but it could be fatal to person, could damage equipment both customer side and exchange side of the systerm if the safety breakers don't active in milli seconds.


An EPR hazard zone could exist in buildings where a HV transformer is located directly next to the building. Remember this potential has no fixed wall barriers and although the transformer can not be viewed by the person located inside their building. That HV transformer maybe located only metres away from him only being separted by a concrete wall.

There are strict distances handed down by the ACMA which installers must abide by. They can all be found in the AS / ACIF S009: 2006 (Appendix H)


These are just a few examples but seek the correct wiring rules for greater guidance.

Type of HV pole or tower Typically looks like this Harzard Zone
Steel lattice tower (220 kV and higher) 40 metres
Pole with 3-Phase or SWER transformer, or with underground power cables 15 metres
HV wooden pole without down conductor to earth electrode or any pole that only supports LV power lines 1 metres





This page was last modified on 25 January 2010 and maybe out of date with regards to its information at the time of reading this article. The information above is only intended for use a guide and should not be relied upon as a substitute for technical advice. Quality Electrics disclaims responsibility for any damage, claim, or liability any person may incur, whether caused by negligence or otherwise, as a result of anything contained in our articles.

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