Earthing and Ground Potential Rise

An earthing system gives fault current a safe, low-resistance path back to its source, holds exposed metal near earth potential, and lets protection operate quickly. Three jobs: protect people, protect equipment, keep the supply stable.

• Fault current: when insulation fails, current flows through the fault path. A good earth path makes the current large enough for a protective device to trip quickly.
• Touch voltage: the voltage between a metal part a person touches and the ground under their feet. Step voltage: the voltage between two feet on the ground.
• Bonding: joining metal parts so they rise and fall together, so no dangerous difference appears between them.
• Earthing is not a substitute for protection devices; it makes them work.

Activity. Draw one simple diagram of a fault in a small installation, showing the fault path, the protective device and where touch voltage appears. Label each in plain words.

Standard to meet. Diagram shows a complete loop from source to fault and back; three terms used correctly.

How well current spreads into the ground depends on soil resistivity, electrode size and shape, and moisture.

• Soil resistivity changes with moisture, temperature, salts and layers. Dry sand and rock are poor; moist clay is better. Measure; do not guess.
• Electrode resistance falls as you add length, depth or parallel electrodes, but with diminishing returns. As a rule of thumb, parallel rods spaced about their own length apart overlap less; the engineer decides the spacing.
• Seasonal change: measure in the driest season, or allow a margin.
• Measurement methods are done by a competent person with a calibrated instrument and a written procedure.

Activity. Rank the three sites in a table of soil readings (ohm-metres) against a target resistance and write which one needs the most extra electrode length and why.

Standard to meet. Rank correctly, give a reason that mentions moisture or resistivity, and claim no final design.

Learn the names and purposes of each part and read them on a drawing.

• Earth electrode: rod, plate or buried conductor in contact with soil. Earthing conductor: links the installation to the electrode. Main earthing terminal: the one point where earthing and bonding meet.
• Protective conductor: runs with the circuits to every exposed metal part. Equipotential bonding: links pipes, structural steel and other conductive parts.
• Earth mat or grid: a buried mesh of conductors used at substations to spread current and limit voltages across the site.
• Records: label every connection point, record test dates and results.

Activity. Mark up a sample single-line drawing with the six parts above and give each one sentence.

Standard to meet. Identify all six parts correctly and keep the labels readable.

When a large fault current flows into an earth system, the ground around it rises in voltage compared with a distant point (remote earth). This rise is called ground potential rise.

• Order of magnitude: GPR is roughly the earth fault current that flows into the earth system times the earth system resistance. A small resistance still gives a big voltage at high current.
• Transferred potential: a metal path (a fence, a cable sheath, a pipe) can carry that rise to a remote point and give a shock where none is expected.
• People and the public: GPR near substations and pylon bases is why we separate or bond systems carefully, and why isolation rules exist for communications and pipes entering sites.
• Control methods: lower resistance, grading conductors, insulating or isolating metallic paths, bonding intentionally, limiting fault current and clearing faults fast. Every design is verified by a competent engineer.

Activity. Calculate the rise for three given fault currents and resistances; list two metal paths in a sample site plan that could transfer potential.

Standard to meet. Calculate three results correctly with units, name two transfer paths, and write a short note saying a qualified engineer designs and approves the controls.

You will not design the system, but you must judge whether a record is complete and whether results are plausible.

• A complete record has: date, instrument and calibration date, method, weather and soil condition, positions, values and the person's name.
• Compare to the design target and to the last result. A sudden rise suggests a broken connection or corrosion.
• Visual inspection: corrosion at joints, loose clamps, cut conductors, missing labels.
• Escalate: any result outside the design limit goes to the responsible engineer promptly, as your procedure requires.

Activity. Review three sample records; mark each complete or incomplete, plausible or suspicious, and write the next action.

Standard to meet. Judge three records with reasons, and name the escalation for any suspicious result.

When the ground around an earth system rises in voltage, a person can be exposed between a touched part and the ground, or between two feet. Learn to work out the simple difference and see who is at risk.

• Touch voltage is the voltage of the touched part minus the voltage of the ground where the person stands.
• Step voltage is the difference between the ground voltage at two foot positions; it falls the further you are from the electrode.
• People at greatest risk are those close to fences, poles, pump houses and substations during a fault, especially when wet.
• Controls include grading conductors, insulating surfaces, keeping people away and clearing faults fast. A qualified engineer chooses and approves them.

Activity. Calculate the touch voltage for each of three pairs of readings (part voltage and ground voltage), rank the three by risk and write one control for the worst case.

Standard to meet. Calculate three subtractions correctly with units, let the ranking follow the numbers, name the control, and note that a qualified engineer approves it.

Some places need extra care because water, metal and people are close together. Learn where bonding is checked and what a record should show.

• Equipotential bonding links incoming metal pipes, structural steel and other conductive parts so they stay at the same voltage.
• Bathrooms, kitchens, swimming areas, farms, workshops and fuel stores each have their own local rules.
• Check for missing links, loose clamps, painted-over joints and unlabelled conductors.
• Do not make or change bonding yourself unless you are competent and authorised.

Activity. Review a sample workshop plan and list three metal parts that need bonding, then write one line on what you would record for each.

Standard to meet. Name three parts correctly, record what, where and who was told on each record line, and attempt no repair as the reviewer.

Earthing work is designed, tested and verified only by qualified, authorised people. Your job in this course is awareness, clear records and clear communication.

• Safe isolation and permits come first: test dead before touching any conductor, and never test or open live earth connections without authority.
• Storms and faults: stay away from earth electrodes and fences during faults or lightning.
• Explain to a non-expert in 60 seconds why earthing and bonding matter at home and at work.
• Next courses: selecting a cable, checking a protection setting, preparing a site test record.

Activity. Write and record (or present to a peer) a 60-second explanation, a one-page checklist for reviewing earthing records, and a three-item next-step plan.

Standard to meet. Explain it so that a non-expert peer understands; write a checklist of at least eight items; put dates in the plan.

On the slide: L1 Basic · Why earth anything

Notes: Say in plain words what earthing protects. Notes: use a washing machine case as the example; no tools needed.

On the slide: L2 Awareness · Awareness of danger

Notes: Name touch voltage, step voltage and bonding. Notes: show one drawing and ask where a person could be at risk.

On the slide: L3 Foundation · Read the parts

Notes: Identify rod, conductor, main terminal and bonding on a drawing. Notes: check labels are readable and complete.

On the slide: L4 Practitioner · Calculate a simple rise

Notes: Work out ground potential rise from current and resistance. Notes: 2,000 A at 0.4 ohm is about 800 V (example values); state it is an illustration, not a design.

On the slide: L5 Specialist · Judge test records

Notes: Judge whether a record is complete and plausible. Notes: a result rising from 2 to 7 ohm (example values) means retest, inspect and report promptly.

On the slide: L6 Advanced · Lead an inspection round

Notes: Plan a round of visual checks and record reviews. Notes: sample three records and mark them complete or incomplete.

On the slide: L7 Super expert · Advise on an earthing programme

Notes: Write an inspection programme and escalation route for a site. Notes: design and approval stay with a qualified engineer; this course gives awareness only.