5 PCB Grounding Methods and 6 Types of Grounding in Circuits
Fri, Feb 26, 2021
What is grounding? Ground wire or the Ground circuit is the current return path to the electrical or electronic power source. In a circuit, it acts as the reference or the 0V plane. It is common that all the other voltages are measured relative to the ground. The scope of grounding does not limit to just the current return path. In electrical power systems, proper grounding is important for human and property protection. A printed circuit board (PCB) having a ground plane blocks Electromagnetic interference (EMI) and improves heat dissipation in the electronics. Lightning protection systems and surge protection systems rely on proper grounding to work properly.
Grounding techniques can be different from application , location to location and even country to country. Here we are going to discuss in detail grounding methods used in the electronic and electrical industry and all the main grounding types.
What Methods are Used in PCB Grounding?
There are few methods practiced for grounding in printed circuit boards (PCB). These methods vary from circuit application and the design practice of the PCB design engineers.
- Method One: Ground Traces
All the components which connect to the ground are connected together from common traces. This is common in old PCBs and simple PCBs.
- Method Two: Common Ground Plane
This is the most common practice in PCB designing. Free space of the PCB which is not utilised by traces or components are covered from the ground place. This method significantly improves thermal characteristics of the PCB and also helps to reduce electromagnetic interference (EMI).
- Method Three: Dedicated Ground Layer
This method is used in multilayer PCBs. Components are connected to the ground plane by grounding vias. Can be found in dense complex PCBs with 3 and above layers.
- Method Four: Grounding Electrical Power Systems
In power system installations all earth connections are connected to an earth bus bar. This bus bar is connected to an earth conductor which connects to an earth rod or mesh.
Earth bus bar collects all the earth wires of all the installations to a common point. The earth resistance of this point should be below 5 Ohms to provide better grounding. High gauge wire is used to connect the Earth bus bar to earthing arrangement. (Earth Rod and Earth mesh)
- Method Five: Equipotential Earthing or Grounding
Equipotential ground means that every conductive element in a protected zone should have the same ground potential.This is achieved by electrically connecting chassis of equipment, metal pipes and all earthing arrangements. This ensures that there is no significant potential difference between any conductive part in the zone and prevents electric shock during a fault.
Types of Different Grounds
- Power Ground
This ground is common for both AC and DC voltages. It is the current return path of the electronic circuit. Without the ground the circuit loop is not complete. Electronic schematics define this ground by the following symbol.
Components which have reference to the ground (0V) are indicated by connecting it’s reference pin to the above symbol. And in the implementation all the terminals which are connected to the ground (GND) are connected together. Since there are plenty of ground connections. Usually printed circuit boards (PCB) have a whole plane dedicated to ground which we will discuss later in this article.
Above symbol is not only used in electronics but also used in large electrical power systems to mention the grounding connection. In the below image you can see that large transformers are referenced to ground. The difference is these grounding connections are often earthed by an earthing rod or a mesh. We will describe more into these types of groundings under the Power system grounding methods.
- Signal Ground
Signal ground is the reference to any analogue or digital signal that is used in the circuit. Most of the time signal ground is equal to the power ground. But in some cases signals in the circuit use a different isolated ground to return signal currents. Which leads to defining a separate ground for the signals. These can be found in sensitive equipment and measuring instruments.
- Virtual Ground
This type of ground is commonly found in Operational Amplifiers (Op-Amps). The point of virtual ground(node) does not directly connect to the ground(GND) current return path but is maintained to match the ground reference potential. Virtual ground is used to analyse the functionality of Op-Amps.
By considering Virtual ground Ground Potential, and assuming no current is absorbed by the Op-Amp, following relation is obtained.
- Surge and Lightning Protection Ground
Lightning protection systems(LPS) and Surge protection systems need a solid ground to dissipate high currents safely. These ground paths have very low resistance and are often welded to structural steel of the building and earthed burying by several earth rods or earth mesh. Equipotential bonding is used between Electrical Power Earth and LPS earth to avoid any voltage difference between earth terminals.
- Grounding in Electric Power System
Earthing or grounding in the electric power system varies among countries. These various types are regulated from the International Electrotechnical Commission (IEC). But each country has their own practices and regulations. Main aim of grounding in the electric power system is to provide safety. Here we talk about the earthing arrangement of Low voltage systems or the power distribution system.
These different earthing arrangements are named with two letter codes.
First letter indicates the earthing arrangement of the power source. (Distribution transformer)
- T - Direct connection to the earth
- I - No direct connection to the earth
- T - Direct connection to the earth. (Usually earth rod or mesh)
- N - Earth is supplied by the electricity network.
There are 3 main categories formed from above arrangements. Which are TT, TN and IT.
TN systems have 3 sub categories which are defined by the arrangement of Earth conductor(PE) and the Neutral Conductor.
- TN−S - Earth conductor and Neutral come as separate conductors and join near the power source.
- TN-C - Earth and Neutral is combined into one conductor called PEN.
- TN-C-S - Earth and Neutral is combined from the power sources as PEN and when it reaches the consumer building it gets separated into two separate conductors of Earth and Neutral.
- Floating Ground
Floating ground happens when a system does not have a solid earth connection. And hence the voltage in the ground terminals and conductors are undetermined. Un-intentional floating ground is considered a fault in the system (potential break in the grounding system). But there are applications where floating ground is intentionally used.
In low voltage supplies and Testing instruments isolation transformers are used to isolate the low voltage ground from the main grounding system to improve the safety. By floating the ground of the low voltage side, It avoids the grounding current path from the main supply. This provides electrical safety if there is a fault at the low voltage side.
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