Skill: Electrical Earthing — Understand What It Does & How It Works
Skill level: 4
Technical
Learning Objective:
To understand the purpose, principles, and importance of electrical earthing in 230V systems — particularly in gate automation, intercoms, and outdoor electrical installations.
1. Overview
What is Earthing?
Earthing (grounding) is the connection of electrical equipment to the earth via a low-resistance path.
There will be an earth terminal at the incoming head connected to the fuseboard. Anything conductive, metal, should be electrically connected to this earth so that in case there is a fault and a live wire touches the metal part then the current will be drawn by the path of least resistance back to the earth terminal. This will draw huge amounts of current which will trip the MCB fuse, as if there was a total short circuit.
It is only used for 110v, 230v and above circuits.
Provides safe route for fault current.
Prevents exposed metal parts from becoming live.
Trips protective devices (fuse/MCB/RCD) within milliseconds.
Protects against fire and electrocution.
Required under BS 7671 / IET Wiring Regulations.
2. Tools and Materials Required
Digital multimeter (continuity + resistance)
Electrician’s loop tester (if qualified)
Green/yellow sleeving for CPCs
Earth clamps, lugs, banjos (for SWA)
Labels or earth bonding tags
Insulated screwdrivers
3. Before You Start
Always isolate supply and prove dead before working.
Never assume earth is present — test it.
If in doubt, call a qualified electrician.
Outdoor systems often degrade — corrosion is common.
Always connect all exposed conductive parts to earth.
4. Principle
4.A Basic Principle
If live wire touches metal casing (or gate) the earth connection allows current to surge to ground.
Fuse/MCB trips rapidly and the metal case becomes safe.
Without earth the casing (or gate) stays live, touching = electrocution.
4.B Methods of Earthing (in Gate Systems)
SWA Cable Armour → Steel braid used as CPC (Circuit Protective Conductor), bonded at both ends.
Separate Earth Core → Green/yellow within 3-core or T&E.
Earthing Rod (TT systems) → Used in remote sites.
Board Earth Terminal → Central point in control board where all equipment earths connect.
4.C Identifying Good Earthing
All motors, metal enclosures or boxes should be connected to each other and to the earth.
Green/yellow wires present and sleeved. Sleeving or taping tells other which cable is the earth.
No floating/cut/broken earths should be present.
Earth continuity confirmed by meter. This needs a qualified electricien to do and will likely have been done in advance.
Clear labelling or tags on bonding points.
4.D Testing Earth
Continuity test between metal case and known earth.
Loop impedance test (if qualified).
Expect low resistance (<1Ω typical).
📌 If high or open readings → call electrician
4.E Types of Earthing
There are several types of earthing arrangements depending on the installation environment and the supply characteristics. In the UK, the two most common types used in gate automation and external systems are TT and PME (also known as TN-C-S). Understanding the differences is essential for safety and compliance with electrical regulations.
TT System (Terra-Terra):
In a TT system, the installation has its own independent earth electrode, such as an earth rod driven into the ground.
The neutral and earth are not combined — the earth path is completely separate from the supply network.
This type is commonly used for external metal equipment such as electric gates, posts, or fences where there’s a risk of contact with the general public, or where the DNO does not permit PME export.
A 30mA RCD is mandatory to provide disconnection in case of a fault, as the earth impedance can be relatively high.PME (TN-C-S – Protective Multiple Earthing):
In a PME system, the neutral and earth are combined in the supply network and then separated at the property.
This is the standard earthing system for most domestic properties.
It provides a low-impedance fault path, but must not be exported to external metal structures (such as gates, fences, or posts) due to the danger of potential rise if the neutral becomes damaged.
When external equipment is connected, a local TT earth or isolation device should be used to ensure safety compliance.
Key Point:
Always identify the existing earthing arrangement before connecting any gate automation or control system. If in doubt, treat outdoor equipment as requiring a separate TT earth to protect users and prevent dangerous touch voltages.
Metal gates with 230v motors should use TT earthing, with an RCD and a earth rod at the gate location.
Wooden gates or gates with 24v motors can use PME earthing as the supply is only powering a transformer inside the control box.
5. Best Practices
✅ Use green/yellow sleeving on all CPCs.
✅ Bond SWA armour at both ends using banjo/earth lug.
✅ Test earth continuity on every job.
✅ Keep all terminations tight, corrosion-free.
✅ Log results in Clik/AppSheet for records.
6. Common Mistakes to Avoid
No earth connection → Electric shock or fire risk.
Earth wire cut/missing → Fault current not discharged.
Loose earth terminals → Unreliable safety.
SWA not earthed both ends → Fault current trapped.
Using earth as neutral → Illegal and extremely dangerous.
7. Safety Information
Relevant SSOW References:
SSOW-01: Electrical Isolation & Lock-off
SSOW-02: Proving Dead (230V systems)
SSOW-04: Working With Mains Voltage
SSOW-07: Outdoor Installations & Weatherproofing
SSOW-11: PPE (gloves, boots, eye protection)
⚠️ Always test earth continuity — never assume.
⚠️ Only electricians should install or test earthing rods / perform loop impedance tests.
⚠️ Without earth, protective devices cannot operate → fatal risk.
