Hi Mr. Thong,
Thank you for your question regarding the recommended interval for testing earthing pole conductivity at an Liquefied Petroleum Gas Plant (LPG). It is out pleasure to help.
When dealing with facilities that handle explosive/flammable materials such as an LPG plant, the concern is primarily with static charge elimination and the reduction of hazardous differences-in-potential. The static charges are eliminated by having an earthing electrode system that has a low resistance-to-earth. The difference in potential between metallic objects is called the Ground Potential Difference (GPD), and is mitigated by the bonding of the various metallic objects together via the earthing system. A low GPD is important to ensure that sparks do not occur and that electronic systems function properly.
The earthing electrode systems should have the resistance-to-earth measured on a regular basis. We recommend that for an LPG plant that you test on a quarterly (every 3 months) basis, particularly in the tank filling areas where static is of such great concern. However, some facilities conduct testing on a every 9-month schedule so as to ensure that changes in the seasons are measured at least on some interval. Other facilities test even less often at 22-month intervals, again so that seasonal variations are taken into account. Here is some information on proper testing of your electrode system:
The Ground Potential Difference is measured by conducting point-to-point resistance measurements from your main electrical service back to various points around your facility. We recommend using a true Direct-Current (DC) meter in flammable areas as it will not spark and provides more accurate resistance data. You should have an earthing system that has less than 0.1 ohms of resistance from any given point in the facility back to your main electrical service. This should be tested on preferably a 9-month interval, or at a minimum a 22-month interval.
We hope that you find this information useful. If you should have any further questions, please do not hesitate to contact us again.
The Engineering Team at E&S Grounding Solutions
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