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Letters to the editor: volume 18, issue 5

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In the June 2023 issue of E&T, readers discuss the prospects of mainstream vertical take-off and landing transport, dangers from on protective earthed neutral conductor failure and more.

Don’t expect widespread eVTOL travel any time soon

I too am struggling to find some credibility in claims about the prospects of urban travel by electric vertical take-off and landing aircraft (‘eVTOL’s Overpromise on Green’, April 2023). Flying at night, or in poor visibility, into a major city or airport would require some of the most demanding piloting imaginable. The act of safely piloting an eVTOL under these conditions, whilst relying upon an already very busy air-traffic control system to separate you from all the other eVTOLS and conventional aircraft, would require a very talented pilot and ATC officer.

I fail to see how any aviation authority could expect to achieve a safe standard of operation by “shortening and simplifying” the certification to that required for a “powered lift”. I would be very surprised to see the UK Civil Aviation Authority going for it, having just gone to great lengths to amend the Air Navigation Order to keep privately operated drones away from airports and built-up areas.

Piloting a commercial passenger-carrying eVTOL flight at present would require an air transport pilot licence and instrument rating at a cost of £100,000 after initially obtaining 1,500 hours of flight time.

We have heard the ‘flying car’ idea numerous times since the invention of cars and powered flight. None of them succeed, largely due to these points.

Carl V Parkin

By email

PEN failure risks are nothing new

Two articles caught my attention in the April 2023 issue of E&T. The first, on protective earthed neutral (PEN) conductor failure (‘Industry must acknowledge dangerous network fault, experts warn’), appeared to present a historical problem as news. Such supply arrangements are known to have inherent risk and have long been prohibited in some installations by the 2002 Electricity Safety, Quality and Continuity Regulations. As we install more non-linear loads in homes and workplaces, neutral currents will only increase and put more stress on ageing networks.

To say that distribution network operators and the Health & Safety Executive ought to “acknowledge the risks” is unfair, as they have long understood the problem. The solution, of course, is to upgrade everything, but some DNOs are reportedly taking months and even years to install new connections. If they don’t have the cash and skills for new developments, there’s little hope for upgrades – an area over which I believe the HSE has little authority anyway. Perhaps we ought to encourage electrical contractors to install earth electrodes when carrying out significant refurbishment work to properties or convert them to TT arrangements – a relatively cheap method of helping limit the magnitude of fire and shock risk following PEN failure.

As head of energy for last year’s Commonwealth Games, I was also interested in ‘How to Reach the Green Goal in Sport’. From a power perspective, I would have loved to have deployed more batteries, overridden planning permissions or moved venues to give more real estate for solar panels or hydrogen storage, but I had a budget and was limited by technology and practicalities.

We relied heavily on venue power and could have used more, but – per my earlier point – the DNO was challenged by the need to upgrade infrastructure to cope with any additional demands. We limited generator use as much as possible, though we still deployed around 26MVA, all running on biodiesel.

Nearly all events, from sporting ones to festivals, need a lot of reliable power for the very short term and there isn’t (yet) a totally green panacea; planting trees to compensate for the carbon footprint is a long-term legacy benefit for what I hope will be a relatively short-term technological problem. I think the time when we can host live events and entertainment with in-person audiences and be truly carbon neutral without offsetting is still a very long way off.

James Eade CEng MIET

By email

Was 1960s cable change a mistake?

The article about fire risk from incomplete neutral circuits in the April 2023 issue of E&T highlights the fire and explosion risk when a faulty high resistance or open neutral causes currents to flow in the bonded gas pipes instead.

Not discussed in depth is the effect losing a neutral has on the supply to domestic properties. This can result in the possibility of wild swings of supply voltage between zero and 415V. Damage and fire risks ensue... and this is not uncommon.

Experienced UK mains engineers from before the 1950s knew all about attaching longer ferrules when soldering four-core mains feeder cables, usually copper, especially in areas prone to ground movement.

The 1960s saw the introduction of cheaper cables using three aluminium cores and a neutral connection via part of the outer wire armour, whereby all jointing was via compression fittings and sealing boxes using resin-filled boxes rather than lead sleeving with plumbed jointing on to the lead sheath. This new form of jointing was cheaper, quicker and no heating process involved of joint seals or sealing compounds, and also required a less skilled workforce.

I believe it has been proved over time that this new method was a less reliable system. Only recently on my estate a complete feeder to a cul-de-sac had to be relaid because of numerous supply issues resulting in fire damage due to a lost neutral.

John Palfreyman CEng MIET

By email

June 2023 Letters Section Cartoon

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Time has come to reassess neutral current risks

Conor McGlone’s report in the April 2023 issue of E&T about warnings of the risks of neutral current diversion reminded me of the early part of my career, when in 1972 following a craft apprenticeship I was appointed senior installation inspector by the then East African Power and Lighting Co for Nairobi, Kenya. Among the engineering problems I encountered was occurrences of electric shock reported by customers, particularly during rainy seasons. I was advised that this was common and was caused by high resistance on the combined protective earthing and neutral (PEN) conductor. The majority of the service cables supplying properties were overhead, so a team of linesmen was dispatched to rectify the problem by tightening line taps.

The 13th Edition of the then IEE Wiring Regulations had statutory force in Kenya but unfortunately for my inspectors was long since out of print, so I set to work editing the then current 14th Edition to a representation of the 13th Edition and adding in some of the company’s requirements for any installation.

Addressing the problem of high resistance on the PEN conductor, I recommended that an earth rod of minimum size 4ft (1.2m) length and 5/8in (14mm) diameter copper be installed. By this requirement I hoped to lessen the chance of shock in event of the high resistance on the PEN conductor. I returned to the UK in 1974 and as far as I know my suggestion was never taken up.

I brought the problem to light at various times during my career and was repeatedly told that although a theoretical problem may exist, the chances of a dangerous occurrence was greatly reduced as the UK has its majority of service cables laid underground and joints are made by solder rather than by mechanical line taps.

Frank Sheldon IEng MIET

By email

Why are smart meters so dumb?

I was pleased to see Mark Scibor-Rylski’s Comment column in the April 2023 issue of E&T on the need for an internal UK energy market and would like to advocate a small but significant addition. We need a standard for communication with smart meters, because they are missing their potential.

The UK does have an energy market – power purchase agreements, the day-ahead market, and the intra-day market – on which large amounts of electrical power are regularly traded. If strong winds are predicted over Wales, a wind farm in Pencelli will sell (in advance) the energy it is about to produce into these markets. Conversely, in a dull patch, a steel rolling mill will decide to pause production because electricity prices are high. This is all well and good and has happened for decades, but the regular consumer doesn’t see any of it – or even know that it exists.

What needs to happen is that our devices respond to these changes. Can they? Well, some could. A fridge, for example, can over-cool food at 4am when prices are low. More significantly, central heating systems reliant on pumped heat can store that heat before people wake up. Personally, I’d be quite happy to have hot water a degree or two colder every now and again if it saves me a fiver, but no, the dumb old electric immersion heater just keeps going at the same temperature regardless.

What is needed here is a standard method for devices like immersion heaters to look at the electricity price right now, and the changes in the next few hours, to allow them to respond.

Arthur Haythornthwaite

By email

Transport needs a decarbonisation plan

It appears that the UK is unlikely to achieve its net-zero target by 2050, and so far there appears to be no plan B. A major part of decarbonisation is transport. For rail, batteries look impractical and fuel cells expensive. But, assisted by a government grant, Cummins has announced a 290hp hydrogen-powered internal combustion engine. That would be better. There’s no reason why the current larger diesels could not also be redeveloped.

A logical strategy for road transport would be similar. Many heavy goods vehicles are already running on HC gas and the government could ask fuel companies to install hydrogen refuelling points at enough existing filling stations and suggest manufacturers should develop hydrogen-powered IC-engined vehicles. Once hydrogen points were available, there would be a demand for such vehicles that would avoid the huge emissions currently resulting from battery manufacture. Buyers would quickly appreciate lower vehicle cost with normal refuelling times, and lower vehicle weights would not increase urban particulates from tyres.

This strategy would allow time for the grid to be updated, for battery manufacture to become zero-carbon, and to develop batteries with lower cost, higher power density to avoid overweight vehicles, and shorter recharging times. Then, the government could revise its policy if it didn’t like IC engines. The public might be disappointed if it did though, having become used to normal refuelling with hydrogen-powered IC engines.

I have nothing against electric propulsion, but wouldn’t this Plan B cause less global emission?

Colin Mynott CEng


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