Grounding and Bonding

What is grounding and bonding?

Grounding and bonding is probably the most discussed issue with the California State Fire Life Safety Technician Exam. The following is based on a solidly grounded conventional wiring system.

The terms are defined in Article 100 and 250.2 of the NEC (National Electrical Code). Section 250.4 provides the performance requirements of Article 250. To make it simple, Grounding is a connection to earth, and bonding is the connection of items to each other.

Electrical bonding is crucial inside a structure, because without it, an ungrounded conductor can come in contact with a piece of metal that someone can touch.  If someone touches that piece of metal they can receive a shock and potentially be electrocuted due to the uncleared fault. A quick explanation for electrical bonding is connecting electrical devices together in the attempt to trip a breaker, if an ungrounded conductor touches surface metal associated with the system.

What does the earth have to do with this? Nothing.

Then why is it called an “Equipment Grounding Conductor (EGC)” in the NEC (National Electrical Code) if it’s primary purpose is to “bond” things together? Simple answer: tradition. It's been this way in the NEC and seems to have been confusing people for a long time. Proposals have been made to change the term, and progress has been made, but the EGC continues to hold water.


Electricity does not seek the path of least resistance to the Earth. It seeks all available paths back to it’s source, in proportion to their resistance. The reason that a person gets shocked when touching an ungrounded conductor and the Earth is because the neutral of the system is repeatedly connected to Earth in a grounded electrical system. The Earth becomes part of a return path to the transformer – it’s part of one route back to the source; the Earth is not the destination for the electricity.


Driving a grounding rod to ‘ground’ any electrical equipment does not provide the low-resistance path required to trip breakers. Driving a grounding rod, or using a Ufer, or a metal water pipe is not a substitute for an EGC. A grounding rod with 25 ohms to Earth will allow almost five amps to escape the system into the Earth when directly energized from a 120V source. Five amps will never trip a 15A or 20A breaker, and in the meantime everything bonded to this grounding rod will be energized to 120V.