Grounding and Bonding 101: What Device Designers Need to Know

When a person is said to be “grounded,” it means they’re stable, sensible and maybe a little bit cautious. Their energy is directed safely and logically to where it’s most productive. As it turns out, the principles of electrical grounding (and its close cousin, bonding) actually aren’t so different. It’s all about making sure that electrical current is directed where it’s supposed to go, and that safety isn’t compromised when the current is going wrong.Polycase’s goal is always to empower our customers, whether that’s through high-quality electronics enclosures, outstanding customer service or expert knowledge. Many of our customers, whether they’re businesses, research labs or hobbyists, design and build electronic devices. Today, we’ll offer a little knowledge on electrical grounding and bonding to help you build and design devices more safely and effectively.

Before we begin, you should note that this is only a general overview of grounding and bonding principles, and isn’t intended to be a complete guide to how to ground and bond a circuit. If you’re new to circuit design, make sure you research best practices for the specific type of device you’re building before you start.

With that said, let’s dive into the definitions of grounding and bonding, the key techniques used to create them and why they’re so essential for electronic device design. Then, we’ll show you how Polycase’s enclosures can help you create stable, properly-grounded and bonded electrical systems.

An electrical ground: Green is a standard color for ground wires in the United States.

What Is Grounding?

The terms ground and grounding have many different uses and definitions in electrical design. The three most useful and important definitions are:

• A physical connection of an electrical system to the Earth (called Earth grounding)
• A return path for an electric current, such as the grounding prong on a grounded electrical plug
• The point at which a current’s voltage reaches zero (used for measuring and benchmarking the voltages of a system’s other components)

These definitions all have a common element: A ground is where an electrical charge wants to flow to get to a zero-voltage state. Voltage, being the difference in electrical potential between two points, is the result of a current trying to balance the potential of the two. Since the current will follow the path of least resistance, grounding can be understood as the science of directing that path safely.

In an extreme (but very simple) example such as a lightning strike, the cloud discharges its negative charge into the positively-charged ground, thereby balancing its charge. By contrast, in a simple battery-powered circuit, the ground might just be the negative terminal on the battery. It’s wherever the current can find a path of least resistance to return to its zero reference level.

Although there are several different types of grounding and thousands of different ways to create a ground within them, we’ll focus on a few key details. First up: Earth grounding, a relatively basic but widely-used form of grounding.

The Basics: Earth Grounding

Earth grounding might not be something you’ll deal with directly when designing electronics, but it’s still important to know the basics of how it works because it forms the basis of accepted best practices for creating safe electrical systems. Particularly, you’ll be figuring your way around Earth bonding systems when you determine how a device interacts with large power supplies such as buildings and offices.

Most residential and commercial power systems have an Earth grounding rod — a highly conductive metal bar that’s sunk into dirt and/or concrete and provides a safety valve for stray currents. (You’ll usually find these outside and/or in the back.) Elements of the electrical system are connected to the Earth grounding electrode via a grounding bar inside the electrical box.

When a fault condition occurs, such as a short circuit or ground fault, the grounding system is there as a safety feature to prevent the system from going hot. Earth grounding also helps protect the system’s components from electrostatic discharges by preventing the buildup of a static charge. Basically, any time an excessive amount of current is flowing through the system, Earth grounding ensures that it has a safe conductive path.

However, the goal of Earth grounding is not just to dump the power into the ground. It’s actually to bring the power back to its supply via a part known as the main bonding jumper that connects with the system’s neutral conductor. This creates an effective ground-fault current path and ensures that a current surge triggers overcurrent protective devices, such as circuit breakers, which then engage and stop the flow of current.

The Basics: Grounded Outlets

If you’re not sure how the grounding prong on an outlet works, now is a great time to learn because it may be relevant in your device design. The two upper holes on an outlet plug are the hot slot (on the right) and the neutral slot (on the left). (Some ungrounded older outlets have only these two.) Current flows from the power supply through the hot slot, energizes the plugged-in device and returns through the neutral slot.

But newer outlets include a third grounding plug. Should a fault current occur (through a short circuit or ground fault), the excess or misplaced current will flow to the ground wire and, in turn, back to the neutral terminal of the power supply, where it trips the breaker. (Again, the grounding prong on the outlet doesn’t actually go to the Earth ground — rather, it sends the current back to the power supply.) This is a key method for making all kinds of electronics safer, and as we’ll discuss later, many are required to have it.

The Basics: Chassis Grounding

However, if you’re designing an electronic device, you may ground the components using a chassis ground. This system involves creating a single grounding point for your device’s circuit. For several reasons, it’s advantageous to have all of your power returns flowing through a single point.

One of the most important reasons to use a chassis ground is that it actually functions as a power distribution system for a device. You can see this most easily in a car or truck. Vehicles use a chassis ground as a way to distribute electrical power to all of the components that need it. A car’s radio, air conditioning, starter and much more all have power flowing through a chassis ground that’s usually on the frame or another metal component of the car’s chassis. Most chassis grounds are connected at only a single point to prevent “ground loops” that can cause interference.

This makes it important to have a conductive chassis in your device. That’s part of why Polycase’s steel and aluminum enclosures are excellent choices for many types of electronic devices. They provide an easy and highly conductive way to ground and bond electronics.

The Basics: Bonding

Bonding is a process that’s related, but not quite identical, to grounding. The key idea is to bring a series of devices to the same electrical potential, even non-current-carrying components such as the electrical enclosure or raceways, so that a fault current doesn’t cause one element of the system to become energized or “hot” (leading to a shock or fire hazard). Bonding prevents this because without potential differences, there’s no voltage seeking a path. In the event of a fault, the current automatically eases and helps prevent a device from going hot.

Although bonding by itself doesn’t protect people or devices, when combined with grounding, it’s a staple of safe electrical equipment design. Main electrical panels include bonding screws or studs to connect the panel’s ground bar with the neutral bar to ensure that the current gets back to the supply so it can trip the breaker. In most electrical design systems, all metal parts in the room that are not designed to carry current will be bonded together using methods appropriate to the application.

Devices That Need Grounding or Bonding

Most electronic devices will require some type of connection to Earth ground for safety reasons. The notable exception is some devices that come with enough internal insulation that they’re considered to already be grounded. This is common for home handyman tools. They’re constructed with two layers of insulation between their electrical components and the drill’s housing. Thus, the manufacturer can make them without a grounding prong on their plug while still producing a safe product.

However, many other devices do require an ultimate connection to the Earth ground. As mentioned above, this will usually come in the form of a chassis ground that allows current to circulate efficiently throughout the device and return to the power supply.

When it comes to deciding whether a device requires grounding, you’ll need to consult the NEC or IEEE standards we’ll discuss below, but there are a few typical conventions based on how much current a device draws and from what it’s made. You’ll often find that fairly low-power devices such as radios, small lamps, clocks, fans and coffee pots aren’t grounded. Higher-powered devices like dishwashers and TVs are always grounded, as are devices made primarily or partially out of metal.

Staying in Compliance with Grounding and Bonding Standards

If you’re building any kind of device that draws electrical power, whether it’s an industrial transformer or a consumer electronics device, you should be familiar with the relevant grounding and bonding standards for that type of device. Non-compliance can be a serious regulatory and safety problem for any institution that manufactures electronics. And if the device you’re building is just for home or hobby use, you may not have to worry about legal standards — but you’re still risking fires and electrical shocks by not properly grounding your equipment.

The National Electrical Code (also known as NFPA 70E) is the standard used by most American municipal governments to regulate electrical installation and design practices. This code focuses mainly on the systems that power residential and commercial buildings, and licensed electricians are trained to work by its standards. It’s important for understanding how devices interact with various electrical system configurations, but it’s not the definitive document on safe power design for electronic devices.

For an in-depth guide to safety standards for device design, you’ll want to consult the Institute of Electrical and Electronics Engineers, a trade organization that represents the accumulated expertise of hundreds of thousands of electronics engineers worldwide. The easiest way to do that is by using the IEEE Standard 1100-2005, also known as the Emerald Book. It sets key safety and efficacy standards in nearly every area of device design, including:

• Handling voltage disturbances and surge protection
• How to effectively shield devices from RF and EM interference
• Conducting a thorough and informative site survey and matching a device’s specifications to it
• Selecting the highest quality and most effective materials
• Ensuring accuracy and efficacy of instrumentation
• Best practices for installing and maintaining devices in commercial or industrial environments
• Special guidelines for devices in the telecommunications and information technology sectors

The Emerald Book will give you the basics, but the IEEE also publishes other electronics design standards that might be relevant to you. That includes industry-specific ones, such as their standard for the oil and gas industry, and equipment type-specific ones, such as low-power integrated circuits. It’s a good idea to check to see which additional standards may be available from the IEEE before you begin your project.

Polycase’s Enclosures for Electronic Device Design

Polycase is an industry leader in high-performance electronics enclosures, and we have several models of enclosures that are well-suited to enclosing devices that need grounding and/or bonding. They also feature the durability, versatility and aesthetic excellence for which Polycase is known.

The stainless steel enclosures in Polycase’s SA Series are great choices for applications requiring grounding and bonding. In fact, each SA Series enclosure comes with built-in metal studs on the door and the base. These provide an easy connection point for grounding and bonding systems. Besides being an excellent choice for grounding, the SA Series is also exceptionally tough and protects against dust, water and corrosion at the rigorous NEMA 4X standard. Its waterproof and rust-resistant construction make these enclosures an outstanding option for outdoor applications like junction boxes and circuit breakers.

Of course, we know how important it is to give our customers a wide range of options, so your choices for metal enclosures for electronics don’t stop there. We offer more great choices like the diecast aluminum AN Series, designed to meet the ultra-rigorous NEMA 6P standard, and the extruded anodized aluminum EX Series, which is perfect for custom electronic devices and includes a pre-molded slot for PCB circuit boards.

There’s much more to learn about the world of grounding and bonding. We’ve just scratched the surface of the basic principles. You’ll need to discover for yourself what the ideal techniques are for grounding your electronic device. But with enclosure expertise on our side, it’s easier than ever to create safe and effective devices with properly configured grounding and bonding.

Still got questions about how our enclosures allow you to ground and bond your electronics effectively? Our enclosure experts would love to help. Just call 1-800-248-1233 or contact us online.