What it is, When it's Good to Go, and How it's Measured
What is Grounding?
Grounding is providing a sufficient path for the flow of electrical charge from the object to the ground. An adequate path allows the charge to dissipate faster than the speed at which the charge is accepted to the part. NFPA 77 states the electrical resistance of such a leakage path may be as low as 1 Mega Ohm, but as high as 10,000 Mega Ohms, and still provide an adequate path. For powder coatings specifically, 1 Mega Ohm or less is used as working ground to ensure proper discharge.
An ungrounded part will accept some voltage and attract some charged powder, but at some point it will begin to repel the charged material. Smaller parts will show these effects more quickly than larger parts. Some difficulties related to poor grounding are:
- Halos around hooks
- Inability to penetrate Faraday areas (fields generated inhibiting electrostatic application, mass of particles cannot penetrate field)
- Inconsistent or low film build
It is very important that powder coaters have good grounding. If the parts are isolated from ground, they can build up voltage to a point and then discharge to ground, creating a potential arc that could ignite powder in the air-stream. So, before using your equipment, take that one extra step to ensure your safety, and check that the parts are not isolated.
What is a Good Ground?
As we stated before, it is important to have resistance less than 1 Mega Ohm to ensure your safety. Most equipment companies use this measurement as a standard.
How is Ground Measured?
You guessed it! Mega Ohms are measured with an ohmmeter! How does it work? One cable is attached to a known ground, and one is attached to the rack content or part. If the resistance to conductivity is greater than 1 Mega Ohm, the system needs to be cleaned.
Additional tests will show specifically where the loss is occurring:
- House ground rod to rail
- Rail to conveyor
- Conveyor to hanger attachment
- Hanger attachment o rack
- Rack to part
For additional information on TCI’s powder coatings, visit tcipowder.com. For more on powder coating hazards and safety, click here to see the troubleshooting guide.