NEC Article 250 Grounding and Bonding: What You Need to Know for the Master Exam

Grounding and bonding is one of those topics that electricians work with every day but struggle to explain precisely. The Master Electrician exam will test whether you know the difference — and the NEC definitions matter.

Grounding vs. Bonding: The Distinction That Matters

The NEC defines these separately for a reason.

Grounding connects the electrical system to the earth. The purpose is to limit the voltage imposed on the system by lightning, line surges, or unintentional contact with higher-voltage lines.

Bonding connects conductive parts together so they're at the same potential. The purpose is to provide a low-impedance path for fault current to flow back to the source, which allows the overcurrent device to operate.

The exam will test this distinction. A question might ask whether a specific connection is required for grounding, bonding, or both — and the answer depends on understanding what each one is actually doing.

The Grounded Conductor vs. the Grounding Conductor

This is another area where terminology trips people up.

The grounded conductor is the neutral — the current-carrying conductor that's intentionally connected to ground. It's typically white or gray.

The equipment grounding conductor (EGC) is the safety ground — the conductor that connects equipment enclosures and metal parts to the grounding system. It's typically green, bare, or green with yellow stripes.

The grounding electrode conductor (GEC) connects the grounded conductor or equipment to the grounding electrode (the ground rod, water pipe, etc.).

Know these three. The exam uses them precisely.

Service Equipment Grounding

At the service, the grounded conductor (neutral) is connected to the equipment grounding conductor and to the grounding electrode system. This is the main bonding jumper connection, and it happens at one point only — at the service disconnecting means.

Downstream of the service, the neutral and the equipment ground must be kept separate. This is why you don't bond neutral to ground in a subpanel fed from another building — the neutral is already bonded at the service.

NEC 250.24 covers this. Know it.

Grounding Electrode System

NEC 250.50 requires that all grounding electrodes present at a building be bonded together to form the grounding electrode system. This includes ground rods, metal water pipes, structural steel, concrete-encased electrodes (Ufer grounds), and others.

If none of the preferred electrodes are available, NEC 250.52 lists what you can use. If you have to install a ground rod, NEC 250.56 requires it to have a resistance to ground of 25 ohms or less — and if it doesn't, you need to install a second rod.

Bonding for Services

NEC 250.92 requires that service equipment be bonded. This includes the service raceway, service cable armor, and all metal enclosures containing service conductors.

The main bonding jumper (NEC 250.28) connects the equipment grounding conductor to the grounded conductor at the service. It must be sized per Table 250.66 based on the size of the service entrance conductors.

Exam Strategy for Article 250

Article 250 is long — over 60 sections. Don't try to memorize all of it.

Focus on: the definitions (Article 100), the grounding electrode system (250.50–250.68), service grounding requirements (250.24–250.30), the main bonding jumper (250.28), equipment grounding conductors (250.118–250.122), and sizing tables (250.66 and 250.122).

Tab those sections. When a grounding question comes up on the exam, you'll know exactly where to look.