What Is a Ground Terminal?
A ground terminal (earth terminal) is a terminal for connecting a ground wire (grounding wire). Grounding is the connection of electrical equipment, the housing of electrical equipment, the neutral point of a line, or the reference potential wiring of electronic equipment to a reference potential point by means of an electrical conductor. It is generally connected to the earth (ground) as a reference.
Uses of Ground Terminals
The intended use of ground terminals is for connection to the grounding wire of electrical equipment and electrical and electronic equipment. The purposes of grounding are safety grounding, functional grounding, and lightning protection grounding. Ground terminals are installed for these purposes on the frames of electrical equipment and electrical/electronic equipment and inside the enclosures that house the equipment, and are used to connect the grounding wire.
*The terms “grounding” and “earth” are expressed as synonyms.
1. Safety Grounding
Safety grounding is a grounding method to prevent electric shock and fire accidents in electrical equipment. It prevents electric shock and fire due to heat generation when leakage current escapes through the ground wire and is touched by a person. For example, in general households, equipment such as washing machines, refrigerators, and microwave ovens are often used with liquids, which may cause a risk of electric leakage, so it is necessary to connect them to the ground terminals.
2. Functional Grounding
Functional grounding is used to stabilize the operation of electrical equipment and the communication of electrical and electronic equipment. Electronic equipment may malfunction due to the influence of electromagnetic waves and various noises from the surroundings. To prevent malfunctions, cover the electronic equipment with a shield and connect the shield to the ground terminals.
As an example, devices that use inverters and other devices that generate harmonics in their control circuits may be charged and emit them into the metal enclosure, causing the device to malfunction. Prevent charging by passing a ground current from the ground terminals to the earth.
3. Other Grounding
Other types of grounding include lightning protective grounding, static protection grounding, and temporary work grounding. Lightning protective grounding conducts lightning current caused by lightning strikes from the ground terminals to the ground wire. Anti-static grounding conducts the current charged by static electricity from the ground terminals to the ground wire. This prevents adverse effects on electrical and electronic equipment, etc.
Principle of Ground Terminals
The electrical connection to the earth having a stable potential is called grounding (earth). The electrical charge that flows out due to leakage of electricity is released through grounding to prevent the main body of electronic equipment from being adversely affected. Electrical circuits in electrical facilities and equipment for industrial applications are grounded.
By grounding the neutral point provided in these circuits (neutral point grounding method), it is possible to prevent power from flowing directly from the high-voltage side to the low-voltage side, even if the high-voltage and low-voltage sides are intermingled. Without grounding, there is a risk of high voltage being transmitted through the wires and damaging electronic equipment.
The neutral grounding method protects the power transmission system by preventing the occurrence of abnormal voltages in the event of arcing and the event of a single line ground fault. Thus, grounding plays an extremely important role in protecting power transmission systems, industrial electrical facilities, and electrical and electronic equipment.
Types of Ground Terminals
There are two types of ground terminals: screw type and one-touch type.
1. Screw-Type Ground Terminals
Figure 1. Screw-type ground terminal
Screw-type ground terminals are used to secure a ground wire with a ring or Y-shaped crimp terminal attached to its end with a bolt on the terminal. For home appliances, the ground wire is stripped to the required length, clamped between washers at the bottom of the bolt, and secured by tightening a screw.
Figure 2. Example of screw-type ground terminal use
2. One-Touch Ground Terminals
Figure 3. One-touch ground terminal (Clip-on)
In the one-touch ground terminals, a ground wire with a crimp terminal attached to its end, or a stripped ground wire, is inserted into the terminal and secured with a one-touch clamp mechanism.
Figure 4. Outlet with ground terminal (One-touch type)
The ground terminal outlet used in homes and buildings is another type of one-touch ground terminal. When the cover of the ground terminals part is opened, there is a terminal hole for inserting a ground wire, and the conductive part of the ground wire is fixed by removing the covering from the tip of the ground wire and inserting the conductive part.
Other Information on Ground Terminals
Size of Ground Terminals
In the case of a distribution board, the size of the ground terminals is determined by the size of the rated current (A) and the thickness of the ground wire.
Note: The size of the terminal for connecting the external protective conductor (PE terminal) is to be determined by the following procedure.
- Determine the cross-sectional area of the external protective conductor from the cross-sectional area of the phase conductor of the power supply.
- From the determined cross-sectional area of the external protective conductor, determine the size of the PE terminal to connect this protective conductor.
Select the appropriate ground terminal size from each manufacturer’s product catalog, etc., based on the external protective conductor sizes in the table above.
Crimp terminals and ground terminals are different. A crimp terminal is one of the connection terminals that is attached to the conductive end of an electric wire and can be fixed or crimped by applying mechanical pressure to the terminal and the wire.