Fundamentals of Grounding and Safety: Protecting People and Equipment

Electrical grounding is used to accomplish several different tasks, but none more important than for the safety of users and equipment while maintaining strict adherence to regulations.

Technical Article September 12, 2024 by David Peterson

Regardless of the industry in which grounding is used, the most important goal is to keep operators and equipment safe. In this article, we will investigate three important factors related to ground conductors and why they solve many operational and safety issues. We’ll also look at which governance guidelines dictate the use of certain grounding principles.

Grounding bus bar inside an electrical panel

Figure 1. The inside of an electrical breaker panel shows the green and bare grounding wires attached to the distribution bar, or ‘bus’.

Grounding for Personnel Safety

For obvious reasons, safety is at the top of the priority list. Not only does personal injury affect the user (that’s the main emphasis), but it can also lead to expensive downtime and liability (which is also a major incentive for companies). These consequences are to be avoided at all costs.

When something breaks on a machine, we usually look for the most likely point of failure first. Often, that happens anywhere that wire connections are established: wire nuts, terminal blocks, screw-down distribution blocks, etc.

If one of these powered wires comes loose and touches the metal casing of an enclosure or the frame of the machine, it can present a dangerous situation. A technician will arrive to troubleshoot the machine and open the cabinet. If they also happen to be touching any nearby metallic object, they may feel a shock with a transfer of current, or worse. Wet environments greatly increase the risk by providing many conductive paths to nearby grounded sources.

Even with a person's high skin resistance, this current may be fatal. This is why these safety aspects are much more serious for higher voltage systems, including household 120V, but especially three-phase and higher voltage systems.

If each of those metallic objects is interconnected with a vast network of wires, then any powered wires that might come loose will touch metal and instantly complete a circuit back to the ground network. Since ground is a very low-resistance circuit, the current in this ground fault will be enormous, tripping any breaker or breaking any fuse almost immediately, which is the whole point of the protection devices.

Equipment Safety and Reliability

Another reason for grounding equipment is for reliable operation. In some rare cases, a transient voltage may exist on a wire near a machine. This may come from a nearby inductive device being turned on and off, like a motor starting up, or it might be from a natural event like a lightning strike.

Grounding rod with acorn nut in the earth

Figure 2. The reason we call it ‘grounding’, or ‘earthing’ - an electrical grounding rod is driven into the earth near the power entrance to a building, keeping all equipment in all facilities at the same potential level.

Ground Wire and Ground Rod

If a wire inside the facility receives that voltage spike, it will cause excessive current to travel down the wire and complete the nearest circuit it can find. If the system is properly grounded through a post into the earth, there will be a brief spike of current in a loop before reaching any equipment, and then return to normal without passing through sensitive devices downstream.

However, if the system is not grounded properly, the nearest path for circuit completion may be through a small printed circuit board (PCB) or controller of a machine, possibly arcing across small traces and control components.

This can lead to the immediate disaster of downtime and replacement of costly control components. Obviously, problems can still be induced right onto the control board itself, but this is why PCB grounding is also a critical factor of system grounding.

Multiple ground connection points

Figure 3. A common connection point for several pieces of a machine - this one bonds the frame to the incoming ground wire from the wall, a PCB ground wire, and also to a grounding terminal block on a DIN rail.

Static Electricity Discharge (ESD)

Different industries will suffer from electrostatic discharge (ESD) in different ways. For some, it may be a non-issue, but for others, the result can be devastating.

Improper ESD protection can result in sparks, igniting any nearby flammable gasses or particulate dust in the air: sawdust, flour, and wheat, as well as any sort of flammable products. As soon as a spark ignites a particle, it will immediately cause an explosion as the flame travels to every nearby particle throughout the air.

These sparks happen when two different conductive bodies are at different voltage potentials. Sometimes this can be a surprisingly high voltage, but the amount of current transferred may be too small to even perceive.

To solve this issue, proper grounding is required to keep all the equipment and control systems at the same neutral voltage level by interconnecting every piece. A proper grounding practice accomplishes this task. Wrist straps, suits, and footwear are tightly controlled in ESD environments to prevent the voltage difference from occurring in the first place.

Every person coming into contact with the environment must also touch a nearby grounded piece of metal, just like you see on the placards on the pumps at the local gas station. Touching metal returns the operator to the same voltage as everything else nearby, and no dangerous sparks can occur.

Wrist strap for ESD grounding

Figure 4. A wrist strap is designed to ground a technician at the same voltage as the equipment being installed or repaired, removing the risk of damage from ESD.

Regulations from NEC Article 250

Grounding specifications are outlined in the National Electric Code (NEC) Article 250 and in several chapters of the UL 508A. These guidelines detail the principles of grounding, the requirements for connecting the system to earth ground outside the facility, bonding machines and metal enclosures, and the requirements for specific wire sizes and other conductors required to establish ground paths.

Adhering to grounding guidelines is required, but it’s also important to clearly understand the purpose of grounding and why these paths exist. With this knowledge, it’s much easier to test and verify that equipment is designed to keep customers, technicians, and equipment as safe as possible.

Want to learn more about grounding and power in control systems? We have plenty more!