What types of preventative maintenance electrical grounding testing procedures do you recommend for electrical grounding systems and how often?
In general, there are three (3) separate procedural items of concern for a facility when it comes to ground preventative maintenance:
- A one-time commissioning inspection procedure for the new grounding system
- A 9-month interval maintenance check conducted by on-site personnel which should also be used after known storms and electrical failures
- A 3 to 5-year intensive inspection/audit conducted by a qualified 3rd party electrical grounding company.
The commissioning process is an in-depth inspection that is designed to establish baseline figures for future comparison. If a grounding rod measured 50-ohms when it was installed, and 50-ohms a year later, but all of a sudden measures 250-ohms on the third measurement (year 2), you would know that something has compromised the grounding rod, and possibly other parts of the system (lightning strike, electrical fault, corrosion, etc.). A good commissioning will involve multiple people, long lengths of wire, and some very expensive and complex equipment.
The annual checks are often designed to be conducted by a single person in only a few hours using a simple hand-held ground resistance meter with the goal being to compare the current results from key areas against the results found during the commissioning. It is typically conducted at 9-month intervals (to make sure seasonal changes in resistance are known), and also after known electrical storms or electrical faults before starting up facility operations.
The 3 to 5-year intensive electrical grounding audit is similar to the commissioning process, in that it will utilize expensive equipment and multiple people, re-checking details of the grounding system that have not been checked during the regular 9-month inspection.
There are a number of different ground resistance tests that we conduct, however they can be primarily broken down into three (3) simple categories: 4-point, 3-point, and 2-point tests.
4-point tests measure the resistance of the earth. We recommend true Direct-Current (DC) and Induced Polarization (IP) meters from AGI USA or the Syscal from IRIS instruments in France.
3-point tests measure how effectively connected a metal object is to the earth. This is often called the resistance-to-ground or RTG. Again, we recommend meters from AGI or IRIS when conducting a 3-point fall-of-potential method. However, if you are conducting a clamp-on induced polarization method resistance to ground test, then there are a number of good quality clamp-on ground resistance meters available. Fluke and AEMC make some of the most common versions:
2-point tests are the most common and similar to many other electrical resistance tests in that we are simply measuring the metallic components of a grounding system back to main electrical disconnect. We recommend AGI or IRIS meters as they are true DC and are also IP meters.
The Engineering Experts at E&S Grounding Solutions