Taking the Low Ground
Rods and Supplemental Options
The challenge is to isolate as best as possible the technical ground from
the power ground (see diagram). That said, auxiliary ground connections that reinforce conduit return paths are recommended. Just make sure all ground connections are from prefabricated, such as conduit connection ground rings, or welded exothermic ground connections. Improvised cabinet ground connection with self-tapping screws are not allowed.
A rule of thumb for a supplemental ground rod is if the resistance of a single ground rod exceeds 25 ohms then a 6-AWG bonding jumper should be used between the grounding rods. The technician must understand that a supplemental earth ground rod is not a replacement for a power safety ground.
Following suggested isolated grounding techniques recommended by the manufacturer is often an acceptable choice. However, know your local codes and be prepared to explain connections to your AHJ; know where the circuit breakers are located; make sure you have proper spacing of low- and high-voltage wiring; know that your wiring gauge meets the equipment load and know any local codes that supersede NEC.
Tips to Remain Well Grounded
It should now be obvious there is no one solution for proper grounding and bonding, and installing electronic systems. The technician must develop an intuitive common-sense approach when installing equipment.
In wrapping up, please note the following handy installation tips for electronic system designers, installers and electricians from Middle Atlantic Products, a provider of engineered mounting solutions:
- Safety comes first: NEC must be adhered to at all times
- Bypassing or lifting safety grounds to reduce noise is dangerous
- Ground loops happen but will not create problems in a properly de-signed system
- Untwisted signal conductors should not be installed in parallel (within 2 inches) or untwisted power conductors
- It may be practical to strap signal cables to power cables in specific cases if the respective conductors are tightly twisted
- Some equipment that passes a small leakage current onto the ground circuit may end up being a hum or buzz in the signal path if proper grounding techniques are not utilized
- Unbalanced signal connections are inherently sensitive to very small ground voltage differences; balanced signal connections are theoretically immune
- Best practices dictate that equipment racks be bonded together per NEC or AHJ; it is best to purchase racks with preinstalled ground studs
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