Jan 16, 2026
Ground Grid Design: The Hidden Backbone of Substation Safety
Summary: A crucial part of substation design is designing the ground grid. A properly designed ground grid protects human operators and mitigates equipment damage in the event of a fault. But engineers must consider a variety of factors before coming up with a ground grid design that works.
Substation design principles dictate building safety redundancy into every new property. Everything a designer can do to maximize safety is considered. Take ground grid design. It might be invisible to the naked eye, but designers and engineers give it considerable weight when developing new substations. It is one of the most critical aspects of keeping people alive when something at the station goes wrong.
The industry standard for ground grid design in substation engineering is IEEE Std 80-2013 – Guide for Safety in AC Substation Grounding. Engineers implement the standard along with a range of other redundancies to maximize safety.
A Word About the Ground Grid
Because substations are high-voltage environments, even the slightest fault could have devastating consequences for anyone who might be on site when it occurs. Designing a ground grid is essential for safety. A ground grid is a network of interconnected conductors buried in the ground in a grid pattern.
Made usually of galvanized steel or copper, these conductors create a low-resistance path that allows electricity to dissipate safely. Both personnel and equipment are protected from direct fault currents caused by lightning strikes and similar events.
A ground grid's effectiveness at dissipating energy cannot be compromised, especially when human lives are at stake. So it is understandable why engineers put so much time and effort into design, testing, and mitigation. The potential consequences of not getting the ground grid right are simply not acceptable.
Common Components of a Ground Grid
Although ground grid design can vary from one project to the next, every grid has four types of components in common:
Horizontal Conductors – Electrical conductors laid in a grid pattern at a depth of 1-2 feet.
Vertical Ground Rods – Rods driven deep into the ground to improve resistivity.
Grounding Electrodes – Rods, plates, or rings that increase soil contact.
Equipment Connections – Connections between metallic parts and the grid itself.
The combination of the four component types maximizes safety and enhances equipment protection. The extent to which each type is required depends on the overall substation design. But you will find all four at virtually every substation.
Ensuring Safety by Preventing Shock
During a fault scenario, the ground underneath a power substation can actually become energized. Grid design must account for this. IEEE 80-2013 standards are designed to protect during such scenarios by preventing two types of potentially fatal electric shocks:
Touch – A person can be shocked by touching a grounded metallic object as current flows from the object into the hand, through the body, out the feet, and into the ground below.
Step – A person can also be shocked simply by stepping on energized ground. Current flows into one foot and then to the other.
Both types of electrical shock can be fatal. There is no way to completely eliminate shock potential because of the nature of how faults occur in a substation. So engineers rely on something known as the 'safety limit formula' to calculate the maximum tolerable voltage a human being can withstand. Then, efforts are made to ensure that the voltage never exceeds the limit in the event of a fault.
The Soil Matters
Proper ground grid design requires a full understanding of the surrounding environment. This includes the soil on which the station will be built. Interestingly, soil is rarely uniform in terms of its conductivity and electrical resistivity. Multiple layers within the same section of soil can have vastly different properties.
To overcome variability challenges, engineers test soil using probes they drive into the ground. Placed in a straight line and at equal distances from one another, the probes inject current into the soil. Engineers then measure the voltage between the probes to calculate resistivity. Through proper testing, it can create a soil model they can subsequently plug into ground grid design.
Design, Test, and Redesign
Soil variability is just one of the many factors that make grid design an evolutionary process. Substation designers rarely get the initial design correct the first time. Instead, they create a grid design and then test it for safety. It is likely to fail the safety check. So it's back to the drawing board for further refinement. Designing, testing, and refining continue until engineers are satisfied with the design's safety.
The design and testing procedure engineers rely on is laid out in IEEE 80-2013. By providing a standard, the IEEE makes it easier for engineers and designers to get their designs right in the shortest amount of time and in a cost-effective way.
Common Mitigation Techniques
Refining a ground grid design often includes mitigation efforts. Here are a few examples of mitigation techniques that address both touch and step electrical shocks:
Crushed Rock – A layer of crushed rock at 4-6 inches offers high resistance. It acts as a resistor between energized soil and a person's feet.
Mesh Spacing – The ground grid is essentially a mesh of cross wires. Adding more wires to create a denser mesh provides more surface area through which electricity can flow, flattening out voltage gradients.
Gradient Control Mats – Along the same lines are gradient control mats. These are dense meshes installed where human operators frequently stand. Installing them ensures that an operator's hands and feet demonstrate the same electrical potential.
Grounding Rods – Driving grounding rods deep into low-resistance soil layers can send current further into the soil. This improves overall grid resistivity.
Ground grid design must also account for potential shocks that could occur miles away. For example, certain types of faults can transmit dangerous levels of current over communication lines connecting a substation to other structures. The best way to prevent this issue is to use fiber optic isolators at points where transformers interrupt the electrical circuit.
Every aspect of substation design is complicated. When it comes to the ground grid, design decisions are influenced by a variety of factors. As such, there is no one-size-fits-all design solution. Each project must be assessed based on its own merits. In the end, safety demands that engineers get it right.
FAQs
Can engineers use a single-layer soil model for determining resistivity?
Theoretically, yes. But the challenge with single-layer models is that they are rarely accurate. Multi-layer models provide a much clearer picture. IEEE 80-2013 suggests a two-layer model at minimum.
How does crushed rock prevent electrical shock?
Crushed rock acts as a high-resistance material between the earth and an operator's feet. It increases tolerable touch and step voltage limits by limiting the amount of current that can physically pass through the body of a human operator.
What is transfer potential and why does it matter?
Transfer potential is the potential for electricity generated during a fault to travel away from the substation to a remote location. A person touching any sort of conductor at that remote location could receive an electrical shock.
Why is 4/0 AWG copper the standard for ground grids?
It is the industry standard because it offers the optimal balance of mechanical strength, thermal stability, and corrosion resistance.
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