house on fire

Rise in deadly electrical faults increasing risk of fires across UK

Image credit: House fire. Photograph: © Photovova |

A type of electrical fault that is putting the public at risk of fires in the UK has increased by more than eight times over the last twenty years in the UK, leading to calls for transparency from experts.

Reports of broken PEN (protected earth and neutral) conductors increased from 57 in 2003 to 474 reports last year, according to a Freedom of Information (FOI) request. As incidents are often not reported, the real figure is likely to be much higher and each incident can affect fifty properties, meaning tens of thousands of properties are likely at risk in the UK.

Broken PEN graph

*not including Northern Ireland

Image credit: The number of reported broken PEN incidents has increased by more than eight times since 2003 *not including Northern Ireland

PEN conductors serve as both a protective earthing and neutral conductor and are used on the PME (TN-C-S) network, which was introduced as an alternative to TN-S and TT in the 1970s.

The PME network was intended as a self-monitoring system to improve safety and provide easy indication if a fault were to occur with the combined neutral and protective conductor. It was also a cheaper alternative to the traditional four core and lead sheath cables. 

But experts say the PEN conductors are particularly susceptible to wear and tear, damage, corrosion and deterioration across an ageing PME network – and given the huge projected load growth on the network, incidents are expected to continue to rise.

When the PEN conductor fails, not only does this present a shock hazard but it generates a diverted neutral current, which can create a significant build-up of heat, as it typically makes a circuit via exposed metalwork such as gas, water and oil pipes. This can cause a fire.

Diagram of broken PEN circuit

Paul Meenan

Image credit: Source: Paul Meenan

Due to the characteristics of not only the PME system but also the water and gas services and other factors such as` steel foundations and the older TT systems, it cannot always be easily identified that there is an issue with the PEN conductor.

The general public, homeowners and even skilled electricians may not know how to assess an installation correctly to identify that there is a potential problem with the PEN conductor.

Paul Meenan, a mechanical and electrical assets manager for the railway operator Trenitalia c2c, said: “broken PEN and diverted neutral currents are a growing challenge for the distribution operators”.

“We need more training information and support from industry including transparency on this to ensure public safety.”

According to Meenan, electricians can measure diverted neutral current, which can indicate whether a PEN is likely break in the future, as resistance on the network may be higher than expected. District network operators (DNOs) are responsible for maintaining a safe supply.

A spokesperson for the Energy Networks Association (ENA), which represent the DNOs, said: “UK energy network operators are working hard to continue improving the resilience of our energy infrastructure. In the past five years the six DNO companies serving Great Britain have spent around £12bn on measures that support increased reliability and resilience.”

The ENA also said the number of broken PENs were “relatively low compared to the actual amount of overhead lines and underground cables on the networks nationally”.

However, one broken PEN incident may affect in the region of 50 properties, meaning tens of thousands of properties could be affected every year in the UK.

The charity Electrical Safety First (ESF) has previously said that 10 per cent of reported broken PEN conductors lead to injury. The charity says an urgent investigation is needed.

Martyn Allen, technical director for the ESF, said incidents involving broken PEN conductors "can and do cause damage to electrical equipment but also present a serious risk of electric shock and fire".

He added: "That’s why Network Operators are required to report broken PEN incidents to the HSE under the Electricity, Safety, Quality and Continuity Regulations 2002. The increase in number of reported incidents is concerning but there are also reports that many incidents go unreported. An investigation into reported and unreported open PEN incidents is needed so we can better understand the scale of the problem, the risk and the solutions needed."

Mark Coles, head of technical regulations at the IET said it was “no surprise” that the number of incidents is rising with the roll-out of electric vehicle chargepoints and heat pumps “adding more load to our local electrical supplies”.

“On paper, PME is a reliable and robust method of distributing low voltage electricity. This is certainly true for new installations but, unfortunately, older parts of the network are failing due to the length of time the distribution cables have been in the ground. Corrosion of joints in the cables can result in the severance of the PEN conductor, leading to overvoltage, undervoltage, neutral current diversion, the risk of electric shock and, in some cases, fire,” he said.

The Health and Safety Executive and the Department for Levelling Up, Housing and Communities have both been approached for comment.



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