Introduction
Grounding electrical systems is critically important for safety, but the National Electrical Code's (NEC) grounding requirements also have some limits and drawbacks. As an electrician, I've learned where the NEC falls short over years of installing and inspecting electrical systems. In this article, I'll share my insights on the key limits and drawbacks of the NEC's grounding rules that electricians should be aware of.
The NEC's Conservative Stance Can Lead to Over-Engineering
The NEC takes a very conservative approach to grounding, erring on the side of caution. This can result in over-engineering grounding systems beyond what is necessary.
For example, the NEC requires a separate grounding electrode system at each building or structure in addition to grounding the electrical system. This results in multiple ground rods being driven even for small structures like sheds and gazebos. While safely grounding smaller structures is important, requiring a full grounding electrode system at every building often feels excessive.
The NEC also requires simultaneous disconnection of grounded and grounding conductors for certain wiring methods. This aims to ensure the ground path is not broken first, but it increases cost and complexity without significant added protection in many cases. The conservative requirements result in unnecessary over-design and higher expenses.
Real-World Example
At one job installing circuits in a shed, I had to drive two 8-ft ground rods and run #6 copper wire to connect them to the shed's ground bus bar simply to meet code, even though the main house's grounding system was just 10 ft away. It met the NEC requirements, but it was overkill for a small shed with such proximity to an extensive grounding network.
Code Requirements Lag Behind New Technologies
Another drawback is that the NEC moves slowly compared to the fast-moving pace of technology. For example, the rise of distributed energy resources like solar photovoltaics and battery storage has created new grounding challenges that the code has not kept up with.
Issues like ground fault detection, grounding portability, and grounding integrated DER systems are not adequately covered in the current NEC. This lags well behind industry best practices. We often have to use manufacturer guidance because the NEC lacks clear grounding guidelines for new technologies.
Real-World Example
I was hired to review a 400 kW commercial solar carport design. The engineer followed the NEC requirements for equipment grounding, but they did not account for functional grounding of the PV arrays on the carport. This is an emerging best practice not yet in the NEC, so I recommended adding perimeter grounding loops to mitigate ground faults. The NEC provided little guidance, so we relied on solar experts and manufacturers.
Separating Grounded and Grounding Conductors Not Always Required
The NEC takes separation of grounded (neutral) and grounding conductors very seriously for good reason, but the separation requirements are excessive in some cases. For example, the code requires running grounded and grounding wires in separate conduits for long feeders and branch circuits.
While separation reduces inductive coupling that could impede ground fault detection, running huge feeders in two conduits instead of one doubles the installation labor and material costs. In practice, inductive coupling rarely causes issues with modern ground fault breakers, so requiring full separation seems unnecessary in many instances.
Real-World Example
I did an inspection of a large commercial install where they ran 500 kcmil feeders in two 4" conduits instead of one to comply with NEC separation rules. It was a huge expense for minimal benefit. With proper conductor spacing and modern breakers, running them in one conduit would have posed little risk. The separation requirements are outdated and drive up costs without much added protection.
Difficult to Apply Grounding Rules Consistently
While the NEC aims to standardize grounding practices, inconsistent interpretation and enforcement of the code's grounding rules leads to confusion. Certain requirements like determining "existing points of attachment" for grounding electrode connections are vague and subjective.
Local jurisdictions often interpret key grounding provisions differently. For large systems crossing jurisdictions, this forces designers to either over-design or risk unexpected change orders during construction to meet varying interpretations. The NEC's vague language leads to inconsistent and confusing grounding requirements.
Real-World Example
I took over a project mid-way through construction when the previous inspector started requiring a radically larger grounding electrode system than the plans indicated. The NEC language related to supplemental grounding electrodes is unclear, so he was asking for a whole new grid of Ufer grounds under the foundation. His interpretation differed from the original local inspector's, forcing us to re-design the grounding last minute at great expense.
Summary
While the NEC's grounding requirements aim to create minimum safety standards, in many cases the rules result in over-engineering, fail to address new technologies, and inconsistently enforce vague grounding guidelines. As an expert electrician navigating these limits and drawbacks, I've learned where following the NEC to the letter makes sense and where it makes more sense to question the code's necessity and applicability. Keeping an open and critical perspective on the NEC allows me to design safe, cost-effective grounding systems.