20.6 High Voltage Dangers & Distribution Systems

High Voltage Dangers & Distribution Systems

Quick Answer: High voltage is above 1000 V a.c. and a general electrical work licence does not authorise work on it. The dangers that kill without contact are step and touch potentials, induced voltage and stored energy. Isolation alone is not enough — HV work requires earthing after isolation by an authorised person, under a permit.

What EPC 48 Asks For

Understanding, not authorisation. You must be able to explain why HV is categorically more dangerous than the 230/400 V systems you are licensed to work on, and to recognise when you are near it. Distribution networks, large commercial and industrial sites, mines and hospitals all put HV equipment in places an electrician walks past daily.

The competence boundary: an electrical mechanic licence covers low voltage electrical installation work. High voltage switching, testing and maintenance requires additional authorisation, training and, generally, a permit system operated by the asset owner or network operator.

Why High Voltage Is Different

Flashover is the key concept. At high voltage, air itself breaks down. You do not need to touch anything — approaching too close is enough, and the distance depends on voltage, humidity and contamination.

Step Potential

When fault current flows into the earth — through an earth electrode, a downed conductor or a faulted structure — the ground around that point rises in potential, falling off with distance.

Because the voltage gradient is steep near the injection point, your two feet stand at different potentials. That difference drives current up one leg and down the other.

Controls and responses:

• Keep well back from a downed conductor or a faulted structure — tens of metres, not a few.
• If you find yourself within an energised area, shuffle out with your feet together or hop with feet together, so no potential difference develops between them.
• Never run, and never take long strides — the longer the stride, the greater the voltage between your feet.
• Earthing grids and gradient control mats are the engineering controls at substations.

Touch Potential

Touch potential is the difference between a conductive structure your hand contacts and the ground beneath your feet. Touching a faulted fence, pole, cable sheath or equipment enclosure can put the full rise-of-earth-potential across your body, on the path most likely to cross the heart.

Controls: equipotential bonding, earth grids, insulated mats and barriers, and keeping out of the area entirely.

Induced Voltage

An isolated and proved-dead conductor can become live again through induction:

• Electromagnetic induction from a parallel energised circuit — an isolated line running alongside an energised line picks up voltage along its length.
• Capacitive coupling from adjacent energised conductors, particularly in cables and busways.
• Back-feed from another supply, a generator, a UPS, a solar inverter or an interconnected network.

Induced voltage is exactly why HV practice applies earths after proving dead. The earths hold the conductor at earth potential for the duration of the work, so induction cannot raise it. Removing earths is a controlled step at the end, under the permit.

Stored Energy

Energy remains after isolation in:

• Capacitor banks — power-factor correction capacitors hold a lethal charge and must be discharged and confirmed.
• Cable capacitance — long HV cables retain charge after disconnection.
• Drive DC buses — observe the manufacturer's discharge time before opening (Section 17.1).
• Batteries and UPS systems — always energised.
• Springs and stored-energy mechanisms in switchgear — mechanical, not electrical, but capable of severe crush injury.

Discharge, prove dead, earth, and only then work.

Creepage and Clearance

Insulator design uses sheds and skirts precisely to lengthen the creepage path. In coastal Queensland, salt deposits on insulators reduce creepage withstand and cause tracking, which is why insulator washing is a maintenance activity on coastal networks.

Never treat a dusty, damp or cracked insulator as intact. Tracking builds a conductive carbon path across a surface that was originally insulating.

Safe Working Procedures Near High Voltage

1. Know where the HV is. Overhead lines, substations, HV cable routes, transformer enclosures, HV switchrooms.
2. Observe minimum approach distances for yourself, your tools, ladders, scaffolds and any plant. Use a spotter where plant could approach a line.
3. Never enter an HV enclosure — locked HV switchrooms, transformer compounds and kiosks are locked for a reason and only authorised persons enter.
4. Treat every downed conductor as live and assume auto-reclose may re-energise it.
5. Work under a permit where you are authorised, with isolation, proving, earthing and access controlled by the responsible person.
6. Do not attempt LV rescue techniques near HV (Section 20.4) — keep back, call 000 and the distributor, and wait for confirmed isolation.
7. Report damaged poles, low conductors, open enclosures and vegetation contact to the network operator.

Recognising the boundary and stopping at it is the professional behaviour EPC 48 is testing.