Grounding vs Bonding: The NEC 250 Distinction That Confuses Everyone

Regulation: NEC Article 250

Keywords: grounding vs bonding NEC, equipment grounding conductor, grounding electrode system, bonding jumper, NEC 250 grounding, neutral grounded conductor, system grounding, equipment bonding

Core Concepts

• Grounding: Intentional connection to earth. Purpose: establish a reference voltage, limit lightning/surge voltages. Does NOT provide a fault-current return path alone.
• Bonding: Connecting conductive parts together to ensure electrical continuity and the ability to safely conduct fault current. Provides the low-impedance path that allows overcurrent devices to operate.
• Equipment Grounding Conductor (EGC): The green or bare conductor that bonds equipment to the system ground. Carries fault current back to the source so the overcurrent device trips.
• Grounding Electrode Conductor (GEC): Connects the system neutral (grounded conductor) to the grounding electrode (ground rod, water pipe, etc.). Does not carry fault current during normal operation.
• Main Bonding Jumper (MBJ): Connects the grounded conductor (neutral) to the EGC at the service. Only at the first means of disconnect — never at sub-panels fed from the same service.

Exam Traps

• The ground rod alone does NOT provide a safe fault-current return path — its resistance is too high. The EGC does that job.
• Floating neutrals at sub-panels are correct — bonding neutral to ground at sub-panels creates parallel neutral paths and is a code violation.
• A green or bare conductor is an EGC — it is not the same as the grounding electrode conductor (GEC), which is sized per Table 250.66.
• Bonding ensures fault current returns to trip the breaker; grounding connects to earth as a reference. Both are needed but serve different purposes.
• Water pipe electrodes must have supplemental electrodes if the pipe has more than 10 feet of metal in contact with soil.

Memory Aid

BOND = connects metal parts together for fault current path. GROUND = connects to earth for voltage reference. Bonding is what actually clears the fault.