Ground Fault Current Path
A ground fault current path is the electrically conductive path that fault current takes from the point where a live conductor contacts normally non-current-carrying parts or earth, back to the electrical supply source. This path can include equipment grounding conductors, metallic raceways, piping, building steel, or the earth itself, but the earth alone is not considered an effective path.
On a shop floor, managing the ground fault current path is essential for shock protection and equipment bonding. Equipment grounding conductors and bonding jumpers provide a low-impedance path from metal enclosures back to the source, ensuring fault current is high enough to trip breakers or fuses quickly. All metallic machine frames, control panels, conduit, and piping must be bonded together to direct fault current along the intended route. WorkSafeBC's Assured Grounding Program requires continuity tests on cords and tools every three months to verify the path is intact. If the effective path is compromised, fault current may flow through unintended routes like building steel or workers, increasing shock and fire risk.
- Relying on earth or incidental metal as the main fault current path, which can result in fault current too low to trip overcurrent devices and sustained touch voltages on equipment.
- Broken, undersized, or improperly terminated equipment grounding or bonding conductors, degrading the effective path and preventing protective devices from clearing faults quickly.
- Equipment inadvertently included in the fault current path, such as motor bearings or structural members, causing damage and shock hazards due to unintended current flow.
How do you distinguish between 'ground fault current path' and 'effective ground fault current path' during an audit?
A ground fault current path is any conductive path fault current could take back to the source, whether intentional or incidental, and may be high-impedance. An effective ground fault current path is intentionally constructed, low-impedance, and designed to carry fault current and operate protective devices. During an audit, map all conductive materials that can connect fault points to the source, then verify which path is continuous, lowest impedance, and directly connected to protective devices and system grounding.
Why is low impedance essential for the effective ground fault current path?
Protective devices require minimum fault current to operate within specified clearing times. Fault current magnitude is determined by source impedance plus fault path impedance. If the effective path has high impedance due to poor bonding or small conductors, fault current drops, causing devices to not trip or trip too slowly, prolonging dangerous touch voltages and arcing. BC regulation expects the fault path to allow at least 5 times the overcurrent device rating to flow for a negligible-impedance fault.
In a Canadian/WorkSafeBC context, what tests verify the integrity of the ground fault current path for portable tools and cords?
WorkSafeBC's Assured Grounding Program requires a continuity test on every extension cord and power tool cord when first put into service, after repairs, and every three months. This test confirms the ground conductor is electrically continuous from the plug ground pin to the tool frame or enclosure, verifying a reliable ground fault current path through the cord and device back to the source.