The original thread:
What am I doing?
I got into an argument with a QC. The craftsman was running the wire from an explosion proof disconnect to building structural steel. I say he was grounding the case. The QC said I was bonding the case. What do you think?
The thread did not get a definitive answer. I came across this.
Mike Holt wrote:
For EC&M Magazine
By Mike Holt, NEC Consultant
Grounding and Bonding - Article 250, based on the 2017 NEC - Part 1
Do you understand how to ground and bond your system?
It’s important to understand the difference between grounding and bonding so you correctly apply the provisions of Article 250.
We earth ground systems to the earth to reduce overvoltage (from lightning induced energy and other events) on the conductors and electrical components (such as transformer and motor windings) of the installation. Grounding metal parts helps drain off static electricity charges before flashover potential is reached. Static grounding is often used in areas where the discharge (arcing) of the voltage buildup (static) can cause dangerous or undesirable conditions.
We bond so that metal parts of electrical raceways, cables, enclosures, and equipment are connected to the supply source via an effective ground-fault current path. To quickly remove dangerous voltage on metal parts from a ground fault, the effective ground-fault current path must have sufficiently low impedance to the source so fault current will quickly rise to a level that will open the circuit overcurrent protection device.