Chapter 1:

Pushing the limits

Nominally, the voltage of the power supplied into Britain’s homes and small businesses should be 230 volts. This theoretical target is the result of what Roger Hey, a former electricity system manager at National Grid Electricity Distribution, describes as a true European-style fudge.

The European Union wanted to harmonise voltage standards so appliances manufactured in one country could be sold across the rest of the trading bloc. Most of the continent had a nominal voltage of 220 volts, with upper and lower limits of plus or minus 6%. The UK likewise had a range of plus or minus 6% but instead centred around a target of 240 volts.

“Obviously the European nations couldn't agree whether to go to 220 or 240,” says Hey, and so “in true European style, there was a bit of a fudge." They split the difference and settled on 230 volts but stretched the limits to plus or minus 10%.

This meant the new standard neatly covered the full ranges of both the previous ones – running from 207 volts at the bottom to 253 volts at the top.

But the standard actually put into UK regulations was slightly different, with a lower limit only 6% below 230 volts, giving a range of 216 to 253 volts.

As intended, nothing really changed as a result of what was, from the networks’ perspective, a harmonisation on paper only. In Great Britain, they continued to aim for 240 volts.

Although there is variation between regions, some above this level and some below, the actual measured average is around 243 volts.

Mark Callum, smart grid development manager at Northern Powergrid, says electricity distribution networks still make very little use of the additional footroom they were given, even though “pretty much all the devices that we buy in the UK have been produced for the European market and therefore they'll be happy all the way down to 207 volts”.

However, other developments are now starting to drive change. “We are at a point in time where our demand is changing drastically,” explains Varvara Alimisi, planning policy and technical development manager at Scottish and Southern Electricity Networks (SSEN). The connection of new loads such as electric vehicle (EV) chargers and heat pumps, as well as domestic generation from rooftop solar panels, means the “voltage landscape” is becoming more complex.

The substantial demand from electric vehicle chargers drags down voltage when they are switched on at night, while heat pumps do the same over the winter. Meanwhile, solar panels drive up voltages during the daytime, particularly over the summer when demand is also lower. Voltage levels are being pushed to greater extremes and becoming more volatile.

Although most customers don’t know what the cause is, and most still relate to network faults, Brian Wann, senior project manager at SSEN, says they have seen a noticeable uptick in complaints relating to voltage. For the time being, Wann says “the numbers are not going ballistic” but they are keen to take a proactive approach to tackling this issue rather than “sitting, waiting” for the problem become worse: “We need to do something now because the solutions, implementation, policy change, funding, etc does take time.”

One problem SSEN is particularly concerned with is electric vehicle chargers tripping when voltage climbs too high. Wann says there was a “misalignment of standards” when the specifications for EV chargers were written, meaning that the range of voltages in which they can operate is “narrower than the band that we actually operate within.”

He says this misalignment is being corrected, but it’s not clear to what extent this problem can be resolved for existing chargers through firmware updates: “I've asked myself and I've not had a straight answer from anyone yet.”

If left unaddressed, Alimisi says the growing variation in voltage will become a barrier to decarbonisation as networks refuse connection requests for fear of pushing voltages outside of the regulatory limits. “When we're trying to connect the customer, it's not about what is happening now,” she notes. “What is going to happen in two years’ time when they connect?”