Martin Plumbridge, Technical Manager at Doepke, discusses RCD protection and looks at whether an RCCB Type B trips on DC.

We have witnessed an increase in reports from several well-informed installers relating to Type B’s that do not function correctly in the presence of DC components. For example, one design was marked as bidirectional but failed smooth DC tripping test. Although the basic requirements of BS 7671 do not require verification that the Type B RCD protection feature works, it would seem prudent to spend a few minutes checking that modern complex domestic systems costing possibly £10,000 or more are protected by a functioning RCD. A simple test with the correct instrument can be performed to verify that the RCD trips when subject to smooth DC.

RCD tests and thresholds

The existing BS7671 1 x RCD verification test required for example for 30mA RCDs relates to an AC sinusoidal residual current, irrespective of the type of RCD.

• All RCCBs subjected to 50Hz residual current are designed to trip between >50% – <100% I∆n, which equates to 15 to 30mA. The max switch off time at 1 x is 0.3s.
• Type A, type F, and type B pulsed residual current (50Hz); the tripping current threshold changes to >35% – < 140% I∆n.

Type A (BS EN 61008-1) must still trip with the pulsed waveform superimposed on 6mA smooth DC.

Type F (BS EN 61008-1 and BS EN 62423) must still trip with the pulsed waveform superimposed on 10mA smooth DC.

Type B (BS EN 61008-1 and BS EN 62423) subjected to smooth DC residual current must trip between >50% – <200% I∆n i.e. for 30mA equates to 15 < 60mA DC on both cycles 0° and 180°.

The standards define the tripping thresholds and times based on the residual current components. Although BS 7671 only requires verification of the AC trip threshold irrespective of the type, Michael Peace’s IET Article in Issue 91 July 2022 explains that other tests are not precluded.

Why DC tripping characteristics matter

RCD Types A and F use a magnetic core to detect imbalance between live and neutral conductors. Smooth DC residual current above the design current can saturate this core, a phenomenon known as DC blinding.

When the core is saturated, The RCD becomes insensitive to further imbalance. Trip thresholds increase unpredictably; the device may fail to trip entirely. This is a major safety concern because a circuit could carry a dangerous fault current without any protective disconnection.

Type B RCDs are designed to detect smooth DC and trip when it exceeds the default value. This maintains sensitivity to both AC and pulsating DC components while also responding to pure DC leakage.

Test instruments

For test instruments equipped with a Type B RCD setting, a multiplier of 2 × I∆n is applied in accordance with the product standard BS EN 62423. We have witnessed an increase in complaints relating to a number of type B’s that do not function correctly in the presence of DC components. Particularly those that are marked as bidirectional. A simple test can be performed to verify DC tripping on DC currents.

Testing procedure for Type B RCDs

The testing procedure for a type B RCD is relatively straight forward from connecting the live, neutral and earth to probes the appropriate terminals on the load side and carrying out the tests. Once complete, carry out the same test on the supply side to check the device is true bidirectional.

• Carry out standard AC test first (following all testing safety procedures).
• DC Tripping test applicable to any 2-pole 30mA type B (Outgoing circuit should be disconnected).

To measure RCD tripping current on a Fluke 1654B

1. Turn the rotary switch to I∆n position.
2. press F1 to select the test current phase, 0° or 180°.
3. press F3 to select the RCD test-current waveform: smooth – DC current to test type B RCD.
4. press F4 to select the RCD current rating (10,30,100,300 or 500mA).
5. press and release ‘test. Wait for the test to complete.

Conclusion

So, does a Type B RCCB trip on DC? Well, the answer is that it should do but some don’t. If it is detecting DC it should trip between >50% – <200% I∆n, which equates to 15 to 60mA range on both cycles 0° and 180° for 30 mA device. If it is truly bi-directional it will trip on DC irrespective of which side, you connect the supply.

The testing procedure for a type B RCD including DC test takes a few minutes in addition to the standard AC test. If it is complex installation requiring Bi-directional RCD functionality you can verify the operation by repeating the test on the reverse side.

Spend a few additional minutes checking that your modern complex domestic system and the people using it are adequately protected by the RCD you have specified and installed.

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It’s been a busy few months in the electrical industry, with new appointments and shake-ups across different sectors. Keep up to date with the latest movements here, as we details who has gone where…

Helen Longdon & Ash Chem

DOEPKE UK

Doepke UK has welcomed two new team members to further support wholesalers, electricians, and contractors nationwide.

Helen Longdon, Marketing Executive, will boost brand visibility and keep the trade informed through clear, timely communications. Ash Chem, Workshop Operative, will assemble switchgear and manage order processing to keep deliveries fast and reliable.

These appointments come alongside the expansion of Doepke’s Daventry premises, increasing stock capacity and streamlining logistics for next-day delivery across the UK. This investment in people and infrastructure strengthens Doepke’s position as circuit protection specialists – delivering quality products, technical expertise, and hands-on support for the electrical trade.

Kristen Brown, Layton Hill, Kas Mohammed, David Pownall & David Williams

SCHNEIDER ELECTRIC

Schneider Electric has announced a series of new appointments to its executive leadership team across the UK and Ireland (UK&I).

Kristen Brown, previously VP Strategy UK&I, will be appointed VP Customer Operations UK&I. Kristen will assume the full scope, previously held by Rhonda Doyle, of the Customer Care Centre, Customer Satisfaction and Quality, Project Management Office, Business Systems and Compliance.

Layton Hill, who has been serving as interim VP Strategy UK&I, will formally assume the role. Layton joined Schneider Electric in 2023 and has played a pivotal role in the Transactional Business team, helping to drive continuous improvement, product commercialisation, and go-to-market strategy.

Kas Mohammed, previously VP Digital Energy UK&I, will assume the role of VP Services UK&I. With an impressive 18-year tenure in Digital Energy, Kas brings a wealth of experience and is well-equipped to share his extensive knowledge and best practice in his new position.

David Pownall assumes the role of VP Power Systems & Safety UK&I. David joined Schneider Electric over six years ago as VP Services & Safety UK&I. During that time, he has successfully driven the growth of the Services business, implemented a new service model, and enhanced employee engagement.

David Williams will expand his remit to include the Major Pursuits team as the VP Transactional Business & Major Pursuits UK&I. David will continue to focus on key customers and segments, ensuring the ongoing development of a robust pipeline for large-scale projects across the territory.

Catch up on previous months ‘Movers and shakers’ articles here

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In this month’s Face to Face we speak with Simon Cranton, Managing Director at Doepke UK, and hear the company’s recent expansion and future plans.

Q. Can you tell us a bit about your professional background and how you came to lead Doepke UK?

I have worked within the electrical industry for nearly 40 years, both in wholesale and as a manufacturer. Initially, I was in sales, and as my commercial experience grew, this led to management positions. I have been Managing Director of Doepke UK for over 20 years, that can’t be right!? Where did that time go?

Q. Doepke UK has been on a growth trajectory recently. What key factors have driven that success?

While it might sound like a cliché, service has been a key driver of our success. By working closely with stakeholders to understand their needs and deliver tailored solutions, we’ve built a strong relationship of trust. Over the years, this has made us a reliable partner that our clients can count on to grow alongside them.

Q. One of the most visible signs of growth is your new building. What does this expansion mean for Doepke UK and your customers?

Our premises in Daventry, Northamptonshire, no longer met our needs as we outgrew the space, so the newly extended building represents a critical step in our expansion. This investment enables us to expand into a larger, more efficient facility, allowing us to support better and provide innovative solutions to the electrical industry. It’s an evolution that strengthens our ability to serve our customers more effectively and drive future growth.

Q. What new capabilities or improvements does the new facility bring?

The new facility brings several key improvements, including six additional offices, state-of-the-art meeting and training spaces, and a designated break-out area (our ‘soft playroom’). These additions are designed to meet the demands of a modern working environment, providing colleagues with the freedom and tools to collaborate, innovate, and thrive.

Q. You’ve also welcomed new team members recently. What roles have been added, and how does this support your strategic goals?

We’ve strengthened key areas across the business. In production, we’ve brought in additional staff to meet growing manufacturing demand. We’ve also expanded our technical team to enhance customer support and grown our marketing function to ensure our messaging is clear, consistent, and reaching the right audiences. As a customer-led business, it’s vital we listen closely, respond quickly, and anticipate where we need to grow – these additions are a direct reflection of that approach.

Q. What do you see as the biggest challenge in the electrical industry today – and how is Doepke UK helping to address it?

One of the biggest challenges for the electrical industry today is keeping pace with the rapid evolution of technology. New products, new installation methods — it feels like there’s always something new to learn. At Doepke, we focus on making things more transparent and more practical. We’re here to support installers with straightforward information. We’ve always been part of demystifying circuit protection.

Q. The heat pump market is expanding rapidly. How is Doepke UK positioning itself in this area?

We developed a unique two module Type B RCCB, which provides an affordable device specific for use with ASHP. Doepke listens to electricians and provides solutions; this has been another excellent case study illustrating this approach. It was clear that a regular Type B RCCB would not be suitable for most heat pumps. We led the way in finding a workable solution, something that the contractor could be confident would meet the criteria.

Q. In the switchgear market – another critical area – what opportunities or trends are you seeing?

This is a crucial part of our business and because we assemble and stock in the UK we have been able to quickly respond to changing demands and provide a fast turnaround of high quality switchgear.

Q. With so much change and growth, how do you maintain Doepke UK’s core values and commitment to quality?

Doepke personnel are key to keeping this; the importance of service runs throughout everything we do. Our collaborations and relationships with customers underpin our commitment to maintaining our high standards.

Q. What excites you most about the future of Doepke UK?

We are constantly developing new solutions and products, and it is more exciting to lead the way than to follow; I find that exciting. Bringing in new team members is part of this journey and enabling them to help shape our future and inject fresh ideas and initiatives.

Find out more about Doepke UK here

Catch up on previous ‘Face to Face’ articles here

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