Top 5 Grounding and Bonding Mistakes to Avoid on the Job

Mistake #1: The Dreaded Improper Neutral-Ground Bond

This is arguably the number one issue flagged by inspectors. An improper neutral-ground bond is most often found in subpanels. The rule is simple: the main bonding jumper (or system bonding jumper) should only be installed at the service disconnecting means or for separately derived systems. In any downstream panel, the grounded (neutral) conductors and equipment grounding conductors must be kept separate. When you bond them in a subpanel, you create parallel paths for return current, turning metal raceways and equipment enclosures into current-carrying conductors. This can lead to what the code calls objectionable current and create serious shock hazards. Strict adherence to subpanel grounding rules is non-negotiable. This often comes up during older home renovations, where you might be tasked with upgrading systems that lack a dedicated ground. Understanding how to properly ground devices in older installations is key to avoiding this critical mistake when adding new circuits or subpanels tied to a single grounded conductor or multiple grounded conductors.

Mistake #2: Misinterpreting Conductor Sizing Rules

Conductor sizing for grounding and bonding is a major point of confusion, and getting it wrong can compromise the entire safety system. It’s crucial to distinguish between the different conductors and the tables that govern them. Proper ground conductor sizing is a hallmark of a professional installation.

Sizing the Grounding Electrode Conductor (GEC)

The GEC connects your system’s grounded conductor to the grounding electrode (like a ground rod). The correct grounding electrode conductor size is determined by the size of the ungrounded service-entrance conductors, as outlined in nec table 250.66. A common error is sizing the GEC based on the overcurrent protection device, which is the rule for the EGC, not the GEC. Remember to consult the rules in 250.66 nec specifically for sizing your GEC or electrode grounding conductor.

Sizing the Equipment Grounding Conductor (EGC)

The EGC is what provides the low-impedance effective ground-fault current path back to the source to trip a breaker or blow a fuse. The rules for equipment grounding conductor sizing are found in nec table 250.122 and are based on the rating of the circuit’s overcurrent device. The complexity of sizing grounded conductor pathways and the EGC itself demands careful attention to detail. This also applies to more complex setups involving parallel conductor grounding. The 2023 NEC has brought changes to these rules, so ensuring you’re up-to-date on how EGC sizing and splicing rules have evolved is critical for compliance. Proper use of the egc electrical component is fundamental to a safe install.

Mistake #3: Errors in the Grounding Electrode System

The connection to the earth itself is often a source of failure. A classic mistake is improper ground rod installation depth; the full 8 feet of the rod must be in contact with the earth. Another frequent issue is poor GEC termination, such as using the wrong type of acorn clamp for direct burial or failing to properly prepare the conductor. Furthermore, the code mandates grounding electrode conductor protection from physical damage. Leaving a bare GEC exposed where it can be easily cut or damaged is a direct violation. Don’t forget that bonding metal water piping is a critical part of the electrode system when it qualifies as a grounding electrode per NEC 250.52(A)(1), as is installing and properly connecting to an intersystem bonding bridge for services like cable and phone.

Mistake #4: Confusing the System Bonding Jumper and Supply-Side Bonding Jumper

While their names are similar, these two jumpers serve different functions. The system bonding jumper creates the critical link between the grounded conductor and the equipment grounding conductor at one specific point. Getting the system bonding jumper location wrong is the source of the `improper neutral-ground bond` discussed in our first point. On the other hand, the supply side bonding jumper ensures that all metallic components on the line side of the service disconnect are bonded together. This is a key part of service entrance bonding, ensuring that if a line-side conductor faults to a metal raceway, there is a path for current to flow that will allow the utility’s fuse to operate.

Mistake #5: Violating the Continuous Path of the EGC

The Equipment Grounding Conductor (EGC) is only effective if it’s uninterrupted. Article 250 of the National Electrical Code emphasizes the need for a continuous grounding conductor from the furthest point of the circuit back to the panel. Mistakes here include relying on a metal box as part of the path without using a bonding jumper, failing to bond concentric knockouts in panels rated above 250V to ground, or using fittings that aren’t listed for grounding. Every connection in the EGC’s path must be robust and reliable. This continuous path is what makes an electrical system truly safe, providing the assurance that a fault will be cleared quickly. Understanding this principle is fundamental to improving electrical worker safety around equipment.

Mastering the Code for a Safer Career

Grounding and bonding aren’t just a chapter in a codebook; they are the principles that prevent fires and save lives. Avoiding these common grounding and bonding mistakes will not only keep your inspection record clean but will also solidify your reputation as a true professional. The rules within nec 250 are detailed and constantly evolving. Staying current with the National Electrical Code is non-negotiable for career longevity and safety. Refresh your knowledge on critical safety codes with our NEC update courses.