One type of electrical fault that is putting the public at risk from fires in the UK has increased more than eight-fold in the past two decades in the UK, leading to calls for transparency from experts.
Reports of broken protected earth and neutral (PEN) conductors increased from 57 in 2003 to 474 reports last year, according to a Freedom of Information (FOI) request. As accidents often go unreported, the true figure is likely to be much higher and each accident can affect fifty properties, meaning tens of thousands of properties are likely to be at risk in the UK.
PEN conductors act as both a protective earth and a neutral conductor and are used on the PME network (TN-CS), which was introduced as an alternative to TN-S and TT in the 1970s.
The PME network was designed as a self-monitoring system to improve safety and provide easy indication if a fault should occur with the combined neutral and protective conductor. It was also a cheaper alternative to traditional four-conductor, lead-sheathed cables.
But experts say PEN conductors are particularly susceptible to wear, damage, corrosion and deterioration in an aging PME network, and given the huge growth in load expected on the network, accidents are expected to continue to rise.
When the PEN conductor fails, it not only presents a risk of electric shock, but it generates a diverted neutral current, which can create a significant heat buildup, as it typically creates a circuit through exposed metal parts such as gas pipes, water pipes, and some oil. This can cause a fire.
Due to the characteristics of not only the PME system, but also the water and gas utilities and other factors such as steel foundations and older TT systems, it is not always possible to easily identify a problem with the PEN conductor.
The general public, homeowners, and even experienced electricians may not know how to properly evaluate an installation to identify that there is a potential problem with the PEN conductor.
Paul Meenan, head of mechanical and electrical resources for railway operator Trenitalia c2c, said: “Broken PEN and diverted neutral currents are a growing challenge for distribution operators.”
“We need more information on training and support from industry, including transparency about this to ensure public safety.”
According to Meenan, electricians can measure neutral current diverted, which can indicate whether a PEN is likely to fail in the future, as the resistance on the network may be higher than expected. District Network Operators (ODNs) are responsible for maintaining a secure supply.
A spokesperson for the Energy Networks Association (ENA), which represents DNOs, said: “UK energy network operators are working hard to continue to improve the resilience of our energy infrastructure. Over the past five years the six DNO companies serving Britain have spent around £12bn on measures that support greater reliability and resilience.
ENA also said that the number of broken PENs was “relatively low compared to the actual amount of overhead lines and buried cables on national networks”.
However, a broken PEN incident can affect around 50 properties meaning tens of thousands of properties could be affected each year in the UK.
The charity Electrical Safety First (ESF) has previously said that 10% of reported broken PEN conductors result in injury. The charity says an urgent investigation is needed.
Martyn Allen, ESF technical director, said iAccidents 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: ‘This is why grid operators are required to report broken PEN incidents to the HSE under the Electricity, Safety, Quality and Continuity Regulations 2002. The rise in the number of reported incidents is worrying “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 necessary solutions.”
Mark Coles, head of technical regulations at the EIT, said it was “no surprise” that the number of accidents was on the rise with the introduction of electric vehicle charging points and heat pumps “adding more load to our local electricity 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 sitting in the ground. Corrosion of the joints in the cables can cause the PEN conductor to break, resulting in overvoltage, undervoltage, neutral current diversion, risk of electric shock and, in some cases, fire,” he said.
The Health and Safety Executive and the Department for Leveling Up, Housing and Communities have both been contacted for comment.
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