The main bonding jumper connects the service neutral wiring to the grounding electrode conductor(s) (GEC), and also to the service enclosure (panel box). By connecting these three components together, it eliminates any voltage potential (current) between them. 

    This is a big deal. “The main bonding jumper at the service panel is the most important electrical connection in the building,” according to Douglas Hansen, an electical expert and one of the authors of the CodeCheck book series. Because of this bonding connection, you can touch the metal panel box and not risk being shocked.

    Modern panels have a green bonding screw at the head of the neutral terminal bar, which indicates bonding. So look for the green screw. The bonding may also be a short strap or wire to the panel box from an insulated terminal bar in some panels, like in the photo above. The grounded (neutral) terminal bar in a service panel is the heart of an electrical distribution system because it ties together with the equipment grounding conductors (ground wires), grounding electrode conductor (wire to ground rod or other type ground), and the service enclosure (panel box) via the bonding jumper.

    Because any subpanels past the service panel must have the ground wires bonded, but not the neutral wires, panels that are designed to be used for either a service panel or subpanel often have a bonding jumper or connector bar between terminal bars that can be removed from the neutral bus for subpanel installations.

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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• What is the maximum number of circuit breakers allowed in an electric panel?

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• What is a tandem circuit breaker? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• How do I identify a combination AFCI (CAFCI) circuit breaker? 

• What does a circuit breaker with a yellow or white test button indicate? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• Why is a fuse box/panel an insurance problem for homebuyers? 

• Why is bundled wiring in an electric panel a defect?

• What is the difference between GFCI and AFCI circuit breakers? 

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?

• Why is an old fuse panel dangerous?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• My circuit breaker won't reset. What's wrong? 

• Why do some breakers in my electric panel have a "TEST" button on them?

• What is the right size electric panel for a house? 

• What do I need to know about buying a whole house surge protector? 

• What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.