The Importance of Grounding Equipment for SafetyApril 22, 2020 by David Peterson
When it comes to electrical grounding, many strategies are employed to accomplish different tasks. One of the main reasons for grounding equipment is for the safety of users and equipment while maintaining strict adherence to regulations.
Regardless of industry, the most important goal of grounding is to keep operators, users, and equipment safe. Many other purposes exist for grounding strategies, but generally, falling short of the priority of reducing losses that come from personnel and machine damage are at the forefront.
The inside of an electrical breaker cabinet showing the green and bare ground conductors attached to the power distribution bar, or ‘bus’.
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 for Personnel Safety
For obvious reasons, safety is near the top of the priority list — not only does personal injury affect the user, but it can also lead to expensive downtime and liability. 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 — perhaps wire nuts, terminal blocks, screw-down distribution blocks, or even points where wires flex and might break on a regular basis. There can be numerous other ways in which the wires come disconnected.
If they come loose and happen to touch the metal casing of an enclosure or the frame of the machine, it can present a dangerous situation. The next person to touch that metal frame who also happens to be touching any nearby metallic object may feel a transfer of current.
Even with the huge skin resistance of a person, 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 complete a circuit back to the ground network. Since ground is required to be very low resistance, 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 critical reason for grounding equipment is so equipment operates more reliably. In some rare cases, a transient voltage may be present on a wire near a machine. This may come from a nearby inductive being turned on and off, like a huge motor starting up, or it might be from a natural event like a lightning strike.
The reason we call it ‘grounding’, or ‘earthing’ - a long bar is driven into the ground near the power entrance to a building, keeping all equipment in all facilities at the same potential level.
If a wire inside the facility experiences 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, it is likely to find a couple of mutually grounded points nearby in both directions, drive current for a short moment in a small loop, and then return to normal.
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.
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.
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.
Static Electricity Discharge
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 — think 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.
Additionally, every person coming into contact with the environment must also touch a nearby grounded piece of metal, exactly like the recommendation just before pumping gas at a gas station. Touching metal returns the operator to the same voltage as everything else nearby, and no dangerous sparks can occur.
A wrist strap attachment harness, designed to ground a technician keeping him or her 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. This guideline details 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.