Key Questions to Ask When Ordering Overhead Line

Use elevating equipment, like dump trucks, backhoes, or cranes.

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Carry long conductive objects like irrigation piping or ladders.

Work at elevation, from ladders and scaffolds or in bucket trucks.

But employees who don’t work for electrical utilities may be less informed or equipped to deal with high-voltage hazards. Here are some questions all workers should ask before they begin working outdoors, if they could be exposed to overhead power line hazards.

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What Are the Hazards?

When workers are near overhead power lines, they may be exposed to hazards that include:

Electric shock. Direct contact with live electrical current results in electric shock, which can kill or injure.

Electrocution. Electrocution occurs when a worker receives a powerful enough electric shock to kill.

Electrical burns. A person who comes into contact with electricity but is not electrocuted may suffer electrical burns on the skin or internally.

Arc flash. Electricity can arc through the air to reach a conductive object. Sometimes an arc produces an explosion—known as an arc flash or arc blast—powerful enough to melt metal and ignite clothing and flesh.

Where Are the Power Lines?

To stay safe, identify all overhead power lines in or near the work area before employees begin working. Make power line locations readily apparent by:

Using caution tape and signs to cordon off the area under power lines.

Forbidding storage of materials under power lines.

Installing flagged warning lines to mark horizontal and vertical power line clearance distances.

How Powerful Are the Power Lines?

The voltage the power lines carry will affect the distance that workers and their equipment must maintain from the lines. Contact the electric utility that owns the lines to confirm the operational voltage of an overhead power line.

Generally, there are three types of lines:

Transmission lines (which typically carry more than 69,000 volts of current)

Subtransmission lines (which carry from 34,500 volts to 69,000 volts of current)

Distribution lines (which carry less than 34,500 volts of current; 13,800-volt distribution lines are common).

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What Safety Precautions Should I Take?

Workers should treat all overhead lines as if they are energized until the electric utility indicates otherwise, or an electrician verifies that the line is not energized and has been grounded. Precautions that can be taken against exposure to overhead power lines include:

Ask if the utility company can shut off the lines while employees are working near them. Always verify that this has been done; never assume.

If overhead lines cannot be shut down, ask the utility company if they can install insulation over the lines during the time employees will be working near them.

In Part II, we will answer the questions Why do I have to observe clearance distances? and How far do I have to stay from power lines?

Are there any risks?

A vast amount of research has been carried out over the past 40 years investigating the potential health effects of EMFs. Despite all that research, there are no proven health effects below the exposure limits. However, there is one area where some uncertainty exists and that’s around childhood leukaemia.

The evidence for this comes from statistical studies, which have found a small increased risk in childhood leukaemia incidence, for children born within 200 m of an overhead line or those with higher average daily exposure (more than 0.4 µT).

Studies have been conducted on mice and rats which show they do not develop the disease when exposed to EMFs in the laboratory. It is unclear whether the increase in childhood leukaemia is caused by EMFs or something else entirely. Therefore, the uncertainty is a weak statistical association only and no causation has been found.

More on the association with childhood leukaemia

The World Health Organization has classified magnetic fields as “possibly carcinogenic” which is the third lowest of four classifications due to this statistical evidence.

Read about the classifications

Recognising that there is this possibility, the UK introduced precautionary measures for overhead line designs to address that potential risk.

UK policy

As the weight of the scientific evidence is against health effects, the UK Government confirmed that other than the exposure limits and precautionary design measure, no further restrictions to exposures are necessary.

What EMFs do overhead lines produce?

What are EMFs

Electric and magnetic fields are produced wherever electricity is used – they are around us all the time in modern life. Overhead power lines – specifically, the wires, not the pylons that hold them up – are one source of these fields.

Electric fields are produced by voltage and magnetic fields by the current flowing through a conductor (wire). Most questions around EMFs relate to magnetic fields.

People are mostly exposed to EMFs from the distribution wires in their neighbourhoods and from wiring in homes. People are also exposed to higher fields for short durations when passing close to electrical appliances that are actively in use.

From the electricity system, high-voltage (transmission) power lines produce higher fields than substations. In the population as a whole, not many people live within 100 – 150 m of a transmission power line. But for those who do, this will also be a source of exposure in the home.

EMFs exposure limits in the UK

The UK Government set exposure guidelines at a national level for EMFs and the electricity system complies with these. The limits are designed to prevent all established effects of EMFs on the body.

The limits followed in the UK stem from an international body called ICNIRP (International Commission on Non-Ionizing Radiation Protection) and are the same limits set by the EU and used in many other countries around the world. ICNIRP is self-constituted but is formally recognised by the World Health Organisation.

National Policy Statement covering the limits

The guideline limits for public exposure are expressed in volts per metre (V/m) for electric fields and microteslas (µT) for magnetic fields. All overhead lines are designed to comply with these limits, even directly underneath them – there is no need for any extra “safe distance” between a property and an overhead line to achieve compliance, and there are no restrictions on how close a property can be to an overhead line. This was looked at by a group called SAGE, but they concluded these measures were not necessary in light of the science.

Power Lines: Demonstrating compliance with EMF public exposure guidelines – A voluntary Code of Practice

What sort of overhead line is near me?

Overhead lines range from lower-voltage distribution lines on wood poles to higher-voltage transmission lines on lattice steel pylons.

Largest overhead lines on steel pylons – 400 kV

EMFs nearly always decrease to background levels in homes within 150 m of 400 kV overhead lines, but most of the time this distance is much shorter. 

For more Overhead Lineinformation, please contact us. We will provide professional answers.