18
GROUND ROD DEPTH BECOMES AN ISSUE WHEN PROVIDING A GOOD
EARTH GROUND
1. Shallow Ground Rod
When the moisture content of the soil is high a ground rod can be driven
into the earth about 1 - 2 feet to provide a low resistance return path to the
holiday detector.
2. Deep Ground Rod
When the moisture content is low the ground rod needs to be driven down
deeper into an area where a higher soil moisture content exists. Driving the
rod deeper helps to reduce the voltage loss in the Earth. Both ground rods,
at the cutback end of pipe and where the Holiday Detector is connected,
typically are driven to the same depth and could be up to 5 feet deep or
greater, in some areas. Soils of this type would be sand, dry clay or very
rocky soils.
PERFORM FIELD CALIBRATIONS TO MAINTAIN A GOOD GROUND
THROUGHOUT THE JOB
SPY
®
highly suggests performing a Field Calibration at the beginning of the
job, at certain intervals during the job, if the soil moisture content becomes
questionable and when changing locations on the same job.
Field Calibration:
When the moisture content of the soil is high a ground rod can be driven
into the earth about 1 - 2 feet to provide a low resistance return path to the
holiday detector.
• How to perform a Field Calibration can be found in NACE SP0490-2007,
Section 3.
• Per section 3.3.1, create a holiday that is approximately 0.031” in diameter.
Ensure that the hole extends completely through the coating to the metal
substrate.
• Per section 3.3.2, start with the lowest test voltage setting of the holiday
detector and slowly increase the test voltage until the manufactured
holiday can be positively detected at normal operating speeds.
• Per section 3.3.3, this method of test voltage adjustment shall be performed
while the exploring electrode and grounding are in the expected operating
position.
To Next Page
Loading...