Choosing the right resistor element for reliable earthing protection

NER data center protection

As electrical networks become more demanding, the role of neutral earthing resistors (NERs) is becoming increasingly important. From renewable energy infrastructure to growing data centre capacity, modern power systems depend on reliable fault protection. That reliability starts with the resistor element itself.

WHY NER DESIGN MATTERS MORE THAN EVER

NERs are designed to limit earth fault currents, helping to protect equipment, maintain system stability and reduce the risk of outages. As power demand grows and networks become more complex, selecting the correct resistor technology is no longer just a specification detail, it is critical to long-term system performance.
Recent industry forecasts highlight the scale of the challenge ahead. According to the UK House of Commons Library, “Data centres currently consume around 2.5 per cent of the UK’s electricity. The sector’s electricity consumption is expected to rise four-fold by 2030.” As infrastructure demand accelerates, dependable fault protection becomes increasingly important.

UNDERSTANDING THE ROLE OF RESISTOR ELEMENTS

Within NER systems, three element technologies have proven particularly effective: edge-wound coils, wire-wound coils and expanded mesh. Each offers distinct advantages depending on the application, operating environment and fault duty requirements.
Selecting the right element is critical to ensuring safe and dependable system performance under fault conditions.

EDGE-WOUND COILS FOR HIGH-ENERGY APPLICATIONS

Edge-wound resistor elements are designed to handle demanding fault duties and high energy absorption. Manufactured from stainless steel strip wound edgewise onto ceramic insulators, they combine high performance with compact construction.
One of their key advantages is the ability to accommodate extreme thermal expansion during fault events. Temperatures can exceed 1000°C, yet the element can expand and contract freely without creating mechanical stress.
This makes edge-wound technology particularly well suited to high-voltage substations and other applications where NERs must safely dissipate large fault currents.

COMPACT AND EFFICIENT WIRE-WOUND SOLUTIONS

For applications requiring higher resistance values and lower power ratings, wire-wound elements provide a practical and economical solution.
Using nickel-chrome or chrome-aluminium wire wound onto ceramic formers, these elements offer compact construction, low inductance and quiet operation. They are often ideal for indoor installations or smaller industrial systems where space and acoustic performance are important considerations.
While they are not typically selected for the highest energy duties, wire-wound coils continue to offer dependable performance in the right operating environment.

EXPANDED MESH FOR RAPID COOLING AND RESILIENCE

Expanded mesh technology offers a different set of advantages, particularly where cooling performance and mechanical resilience are priorities.
Its open structure promotes unrestricted airflow, allowing elements to cool significantly faster than traditional stamped grid designs. The lightweight construction also provides natural shock absorption, making expanded mesh suitable for rail, offshore and other vibration-prone environments.
Low inductance characteristics further improve electrical performance, while rigid Omega-shaped designs help maintain safe spacing between elements during high-temperature operation.

THERE IS NO ONE-SIZE-FITS-ALL APPROACH

Selecting the right resistor element depends on several factors, including fault current levels, duty cycle, environmental conditions, available footprint and maintenance requirements.
Understanding how each element behaves electrically, thermally and mechanically is essential to ensuring reliable protection performance over the lifetime of the system.
With more than 100 years of resistor engineering experience, Cressall works closely with customers to design NER solutions tailored to each application and operating environment.
Need support selecting the right NER element technology for your system? Contact the Cressall team for expert guidance and application-specific advice.

The silent guardian

The silent guardian

How resistors protect data centres from electrical stress

The data centre market is booming thanks to AI. According to Goldman Sachs, the explosion in generative AI means demand for data could increase 50 per cent by 2027 and by as much as 165 per cent by the end of the decade compared to 2023’s figures. It’s clear data centres are fast becoming another lifeblood utility in modern society, but what would happen if one suddenly switched off? Here, Mike Torbitt, Cressall‘s managing director, theorises just how much our world will rely on data centres in the future — and how to ensure their reliability.

Just as water, electricity and internet access have become utilities essential to modern life, information itself — stored, processed and delivered via data centres — is emerging as another utility of the digital age.

Goldman Sachs estimates that current power usage by the global data centre market sits at around 55 gigawatts (GW) and is comprised of cloud computing workloads and traditional workloads for typical business functions such as email or storage and AI.

Currently, the analyst estimates AI makes up roughly 14 per cent of this 55 GW capacity. However, when modelling future demand for these workload types, its analysts predict data centre power demand could reach 84 GW by 2027 with AI growing to 27 per cent of the overall market.

Of course, this is just one of many predictions and the crystal ball is present during any discourse on AI’s future. What appears definite though, is that the technology is transforming the way we consume information and thus the capacity of data centres.

Lights off

So, what would happen if a data centre suddenly lost power? The effects could ripple far beyond disrupted websites. Online banking, medical diagnostics, AI-powered logistics and smart energy infrastructure are just some of the many applications that rely on a continuous flow of information being processed and stored in these facilities.

For AI-specific workloads, the risks are particularly acute. Training large-scale models involves thousands of simultaneous graphics processing and tensor processing unit operations that can run for days or weeks. If power is lost mid-process and checkpointing isn’t frequent or robust, entire training runs may be corrupted or lost. Inference systems that run in real-time such as recommendation engines, chatbots or fraud detection tools can stall instantly, causing service degradation or outright failure.

Data integrity is another issue. Many applications run on distributed databases that rely on synchronous replication and consensus mechanisms. If nodes in different racks or zones go down at slightly different times, it can cause data inconsistency or split-brain scenarios, where systems disagree on the current state of data.

While most modern data centres are equipped with uninterruptible power supplies (UPS) and backup generators, a delay in switching over to backup power, a failed UPS battery bank or insufficient fuel reserves in a prolonged grid failure can all lead to downtime.

Powering resilience

As data centre workloads become more complex and the stakes of downtime more severe, electrical reliability becomes a critical point of failure and therefore, a primary design consideration. This is where passive components like resistors play a role in ensuring stable, resilient operations.

Resistor technologies such as neutral earthing resistors (NERs) are essential to protecting infrastructure and maintaining uptime. NERs are deployed to limit fault current during earth faults, preventing damage to expensive components like transformers and switchgear. In the event of a ground fault, an NER ensures the fault current is safely controlled and isolated, allowing the rest of the data centre to remain operational while the fault is addressed.

Load banks, on the other hand, are used to test and validate backup power systems by simulating real electrical loads under controlled conditions. They allow operators to verify that backup systems can deliver the required power reliably during an actual outage, without the risk of affecting live data centre operations.

Routine load bank testing can uncover issues such as fuel delivery problems, battery degradation or improper load sharing between generators — all of which might otherwise remain hidden until an emergency strikes. By identifying and correcting these issues in advance, load banks support predictive maintenance, regulatory compliance and, ultimately, system resilience.

Making the choice

Of course, not all resistor solutions are created equal. As data centres scale, operators must consider variables such as fault current levels, system voltage, spatial constraints, cooling requirements and compliance with international standards.

Selecting the appropriate NER with the correct resistance value and time rating, how long the resistor can safely carry fault current before its temperature exceeds safe operating limits, is critical for effective fault current limitation without interrupting service. Likewise, load banks must be sized to reflect real-world power demands and designed for integration with both generator and UPS systems.

Custom engineering plays a significant role in aligning these technologies with the architecture of each facility. Modular data centres, hyperscale environments and edge computing sites each present unique demands — from space and airflow limitations to maintenance accessibility. Working with experienced resistor manufacturers, like Cressall, ensures that resilience is built into the system from the ground up, not added as an afterthought.
In a digital economy that’s becoming increasingly dependent on uninterrupted data flow, choosing the right components to ensure reliability matters. As the utility of the modern world, the cost of downtime in data centres is only going to rise as our implementation of AI technologies increases. Building safety nets into systems is therefore critical and, while resistors may not be the first component that springs to mind, their role in data centre uptime has never been more important.

Learn more about Cressall’s range of resistor technologies by visiting the website

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Lessons from COP30

Lessons from COP30

The critical role of grid stability in the energy transition

‘We can choose to lead, or be led to ruin,’ declared UN Secretary-General António Guterres, addressing delegates at COP30 in the rainforest city of Belém, Brazil. As the world pushes to triple renewable power capacity by 2030, attention is shifting from adding generation to preparing grids for the change. In light of COP30, Mike Torbitt, managing director of resistor manufacturer Cressall Resistors, examines the growing pressure on electricity networks and the role of grid stability technology as renewable deployment accelerates.

The world has recently seen record growth in renewable energy, with solar and wind forming the backbone of global decarbonisation efforts. Yet, despite that, COP30 delivered a clear message: the pace must quicken if we are to meet targets for 2030. Analysis from the Climate Action Tracker coalition, released at COP30, shows that “sticking to key climate pledges — tripling renewable energy, doubling energy efficiency and cutting methane emissions — could avoid nearly 1°C of global heating and significantly slow the rate of warming this century.”

Expanding renewable capacity at the pace needed to meet climate goals will demand unprecedented investment, infrastructure expansion and system upgrades. But increasing generation alone won’t be enough — the real challenge lies in ensuring that grids can handle the variable, fast-responding energy these new sources provide. Integrating that power reliably into networks that were not designed for variable energy sources is becoming the defining task of the energy transition.

The grid challenge behind rapid renewable growth

Renewable growth is radically changing the way in which electricity systems function. Solar and wind generation follow weather patterns, leading to steep rises and falls in generation that must be balanced in real time. As installations expand, these variations become more extreme, placing new stresses on equipment and system operators alike.

Today’s renewable output is constrained by congestion and capacity limits in transmission and distribution systems, limiting how efficiently the power is delivered to consumers. Storage capacity is expanding but remains far below what is required to balance supply and demand across all regions.

Without the right stability and protection technologies, high-renewable grids risk greater levels of curtailment, decreased asset lifetimes and reduced system reliability. As inverter-based generation becomes the dominant form of new capacity, networks are also losing the inherent stability once provided by conventional rotating machines. This shift makes grids more sensitive to faults, fluctuations and power disturbances, increasing the importance of technologies that can absorb, dissipate or smooth unexpected energy spikes.

Technology that makes high-renewable grids possible

This is where resistor technology becomes essential to keeping systems stable. Dynamic braking resistors (DBRs) offer a proven method for managing rapid changes in power flow, especially in systems where renewable output can increase or decrease quickly. By safely converting excess energy into heat, DBRs prevent over speeding in rotating equipment or instability in inverter-driven systems.

For wind turbines, DBRs are essential to managing sudden gusts or rapid changes in mechanical load. For solar, they support stability during cloud transients or fast inverter cycling and in storage and hybrid systems, they help maintain smooth operation during transitions or when switching between energy sources. At commissioning stage, DBRs also support system testing to ensure equipment performs safely before going live.

Cressall has decades of experience across renewable generation, grid infrastructure and transport applications, supplying DBRs engineered for long-term reliability, safety and demanding environmental conditions. As grids continue to evolve, this technology will continue to support the safe integration of new renewable capacity, especially in a future where inverter-based systems take on an increasingly large share of total generation.

What COP30 signals for the future

One of the key messages emerging from COP30 is that renewable growth must be matched by investment in modern, stable and flexible grids. The International Renewable Agency’s (IRENA) analysis reinforces this point, stating that “power system infrastructure and flexibility must expand at a much faster rate to accommodate rising shares of variable renewables”.

According to IRENA, at COP30 the Utilities for Net Zero Alliance (UNEZA) announced investment plans totalling over USD 1 trillion by 2030, with a significant emphasis on strengthening power grids and networks. This commitment from the world’s leading utilities demonstrates the scale of infrastructure transformation needed to support renewable expansion.

This has significant implications for grid operators, developers and technology suppliers. As renewables are installed more rapidly, system stress will rise and there will be greater need for proven solutions that ensure stability.

Digitalisation will play a growing role in improving forecasting and control, but physical safeguards such as DBRs will still be essential for protecting equipment and maintaining reliability.

COP30 reinforced the scale of work required to reach renewable and climate goals. But that transition cannot succeed unless grids can cope with the new realities created by variable, fast-responding, decentralised generation. Dynamic braking resistors offer a crucial layer of protection and stability, enabling renewable energy sources to be integrated in a secure and reliable way.

To find out more about the role of resistors in renewable energy generation, speak to Cressall’s experts

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The resistance to renewables

The resistance to renewables

Why are energy providers abandoning net-zero strategies?

Oil and gas giant BP recently walked back the net-zero targets it introduced in 2020, saying the company had moved ‘too far, too fast’. The announcement is part of a worrying trend of energy providers and other multinationals reducing or watering down their sustainability strategies. Here, Mike Torbitt, managing director of Cressall, explores the causes behind this movement and explains the role that resistor technology can play in meeting sustainability targets.

In February 2025, BP announced plans to cut its budget for renewable projects by $5 billion, while simultaneously increasing its investment in fossil fuels to $10 billion per year.

The decision will see the oil giant produce 2.4 million barrels of oil per day by 2030. Given that just 36 fossil fuel companies are responsible for over half of the planet’s emissions, this step backwards has a hugely damaging potential.

But BP is not the only energy provider to backtrack on its sustainability commitments. The move comes a year after fellow oil giant Shell dialled back its 2030 target to cut net carbon intensity from 2016 levels, lowering its goal from 20 per cent to a range of 15 to 20 per cent. But why are energy providers turning their backs on these objectives?

Profit versus planet

Currently, renewable energy projects such as wind and solar are simply not returning as much profit for oil and gas companies as fossil fuels. According to 2023 figures from NPR, US companies producing oil and gas could expect to make a return of between 20 and 50 per cent return on investment on the capital invested into projects. For solar and wind projects, the estimated figure stands at just five to ten per cent.

Consequently, there is less investor interest in the stocks of oil companies that are diverting their budgets towards wind and solar. Take for example the five-year period between the end of 2019 and the end of 2024. New York Times data shows that BP’s stock prices fell by 19 per cent and Shell’s grew by around 15 per cent. Meanwhile, the stock price of competitor Exxon Mobil, which did not invest in wind and solar energy, grew by over 70 per cent.

There are a few major barriers to profitability. The first is that oil companies may lack the sector-specific experience required in order to succeed with wind and solar projects.

Exxon Mobil instead chose to invest in hydrogen and lithium extraction, since the skills needed are very similar to those used in extracting oil. While the mining of these elements comes with its own environmental concerns, both are vital components in the production of battery-powered vehicles.

A second factor affecting profitability is the high initial investment costs for renewable projects combined with the low prices of solar and wind power. This means that it takes years, or even decades, for investors to see return on investment.

Improving infrastructure

While these energy sources have become less expensive to generate in recent years, they tend to produce energy during the same time periods. For instance, on a particularly windy day, the wind energy produced will outstrip demand, which drives down prices. Additionally, wind turbines are increasingly being turned off as the grid is unable to cope with this surplus.

One solution to this issue is using interconnectors, high-voltage direct current (HVDC) cables that connect the energy grids of different countries, enabling the movement of renewable energy to international markets where demand is higher. HVDC technology is ideal for long-distance transmission with minimal energy losses.

In HVDC systems, resistor technology plays a vital safety role by dissipating excess wind energy during faults, helping to stabilise the grid and prevent damage. DC neutral earthing resistors also add a further layer of protection to HVDC converter transformers, both offshore and onshore, by managing fault currents and ensuring system reliability.

Ultimately, privately owned oil and gas companies are more likely to be driven by shareholder interests than they are by environmental targets. However, by ensuring that the correct infrastructure is in place to make the most from the renewable resources, it’s possible to improve both sustainability and profitability.

Looking for a reliable resistor partner for your HVDC project? Get in touch with our knowledgeable team.

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