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| More Ground Resistance Applications
Application Sites
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| A typical setup at a cellular tower installation | There are four other particular applications where you can use the Fluke 1625 to measure the capability of the earth ground system.
Cellular Sites/Microwave and Radio TowersAt most locations there is a 4-legged tower with each leg individually grounded. These grounds are then connected with a copper cable. Next to the tower is the Cell site building, housing all the transmission equipment. Inside the building there is a halo ground and a MGB, with the halo ground connected to the MGB. The cell site building is grounded at all 4 corners connected to the MGB via a copper cable and the 4 corners are also interconnected via copper wire. There is also a connection between the building ground ring and the tower ground ring.
Electrical SubstationsA substation is a subsidiary station on a transmission and distribution system where voltage is normally transformed from a high value to low value. A typical substation will contain line termination structures, high-voltage switchgear, one or more power transformers, low-voltage switchgear, surge protection, controls, and metering.
Remote Switching SitesRemote switching sites also known as slick sites, where digital line concentrators and other telecommunications equipment is operating. The remote site is typically grounded at either end of the cabinet and then will have a series of ground stakes around the cabinet connected by copper wire.
Lightning Protection at Commercial/Industrial SitesMost lightning fault current protection systems follow the design of having all four corners of the building grounded and these are usually connected via a copper cable. Depending on the size of the building and the resistance value that it was designed to achieve, the number of ground rods will vary.
Recommended TestsEnd users are required to perform the same three tests at each application: stakeless measurement, 3-pole fall-of-potential measurement and selective measurement.
Stakeless MeasurementFirst, perform a Stakeless measurement on:
- The individual legs of the tower and the four corners of the building (cell sites/towers)
- All grounding connections (electrical substations)
- The lines running to the remote site (remote switching)
- The ground stakes of the building (lightning protection)
For all applications, this is not a true ground resistance measurement because of the network ground. This is mainly a continuity test to verify that the site is grounded, that we have an electrical connection, and that the system can pass current.
3-pole Fall-of-potential MeasurementSecond, we measure the resistance of the entire system via the 3-pole Fall-of-potential method. Keep in mind the rules for stake setting. This measurement should be recorded and measurements should take place at least twice per year. This measurement is the resistance value for the entire site.
Selective MeasurementLastly, we measure the individual grounds with the Selective test. This will verify the integrity of the individual grounds, their connections, and determine whether the grounding potential is fairly uniform throughout. If any of the measurements show a greater degree of variability than the other ones, the reason for this should be determined. The resistances should be measured on:
- Each leg of the tower and all four corners of the building (cell sites/towers)
- Individual ground rods and their connections (electrical substations)
- Both ends of the remote site (remote switching)
- All four corners of the building (lightning protection)
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