NCD can cause fires and gas explosions

HSE refuses to act over dangerous electrical fault

Image credit: House on fire. Dreamstime

The Health and Safety Executive (HSE) has broken its silence over an increasingly common dangerous fault on the electricity network, after a member of the House of Lords intervened following an E&T article in February.

Responding on behalf of the government to a question from Labour Lord Rooker, Viscount Younger of Leckie said HSE officials had been advised that “neutral current diversions (NCD) are a known phenomenon and can occur for a number of reasons”.

Younger added that the HSE had “monitored developments carefully and continues to do so”. However, he said officials “were of the view that no additional action is required by the regulator to manage this risk of neutral current diversion at the present time.”

Experts have said the response is disappointing and have called for more transparency.

In February, several electrical experts told E&T that there was a real risk of deadly gas explosions and fires in the UK due to NCD. They argued that the HSE needed to acknowledge the risks of NCD so that a programme of testing can be implemented - and lifesaving upgrades made to the grid.

An NCD can occur on the network when the combined protective earthing and neutral (PEN) conductor fails. The current is then diverted by making a circuit via exposed metalwork on buildings including gas, water and oil pipes. This can lead to a significant build-up of heat, leading to fires and gas explosions.

PEN conductors are particularly susceptible to damage, corrosion and general wear and tear across an ageing PME (protective multiple earthing) network – and given the huge projected load growth on the network, incidents are expected to continue to rise.

Last year, E&T revealed that the reports of broken PEN conductors had increased by more than eight times over the last 18 years in the UK from 57 in 2003 to 474 reports in 2021. One broken PEN incident may affect in the region of 50 properties, meaning tens of thousands of properties could be affected each year in the UK.

Former SP Energy Networks (SPEN) employee Gordon Mackenzie, who is trying to raise awareness about the dangers of NCD, said it was “a really good thing for public and operative safety that the risks associated with NCD have been highlighted and raised at the highest levels”. But he said the answers given “fall short on technical detail and leave me questioning the data and information used by the HSE to get to the declared position”.

“I hope that there will be a continuing industry-wide collection of electrical testing data and knowledge sharing, to allow the HSE and others to fully appreciate the associated risks, and to carry out a future review as soon as possible,” he added.

Paul Meenan, senior asset manager for rail firm C2C and chairman of a subgroup of the Electrical Safety Roundtable, an industry forum dedicated to enhancing the standards of electrical safety across the UK, said he remained “disappointed by the HSE stance”. He called “at the very least for transparency” and said that data should be made available “so industry can assess and better manage risk locally”. 

Industry sources say many reported appliance failures, which have led to fires, were in fact a result of NCD. The fault can cause gas explosions, according to Mackenzie. While the cause of the majority of gas explosions are recorded as gas leaks, he noted that NCDs are so prevalent on gas pipes that the gas industry attaches jump leads between gas pipes before changing them, because they generate sparks.

In its written response, the government added that the Gas Safety (Installation and Use) Regulations require additional electrical bonding when cutting conducting gas pipes to minimise the risk to workers.

However, Mackenzie said these measures were not adequate and would not mitigate the risks associated with the heightened levels of current that can flow through gas pipes where NCD exists. He also pointed out that any metallic piping could carry the current, including water and oil pipes, which are not covered under these regulations.

The HSE has been approached for comment.

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