GEWISS recently launched ReStart, the exclusive intelligent RCD, designed to safely test and reclose after a nuisance trip such as a lightning strike. Here our technical specialist provides an overview of the benefits of this exciting innovation.
What are (ARDs)?
ARDs are Automatic Reclosing Devices. Intelligent devices that simply reclose all by themselves.
Only if safe to do so! This article concentrates specifically on self-resetting RCD versions.
Why are ARDs an important part of an installation?
Devices such as RCDs are very good at their job. They are sensitive devices which have purposely been designed to protect the electrical system, humans, and livestock. However, they also have some disadvantages:
Once the device has tripped (as expected and designed to do so) the power is shut off and stays off, until someone manually resets the RCD. This manual reset will be required even if the “fault” was temporary, or a nuisance trip. For example a power surge, a lightning strike, or a blown lamp, There are many reasons for “nuisance trips”. These “nuisance trips” are only present for a brief moment, and therefore almost immediately after the power shuts off the circuit is safe again. However, the RCD will remain unnecessarily isolated until manually turned back on. This is where the ARD takes over.
The ARD will test the circuit after a trip and if safe, only if it is safe it will restore the supply. These nuisance trips are not only an inconvenience, but they can cause major problems within industry; with unnecessary downtime, loss of stock (for example in temperature controlled environments) resulting in loss of customer satisfaction if services are interrupted, there are many more issues. The cost of this can be enormous.
ARDs are the only solution to resolve all the unnecessary issues that occur because of an untimely spontaneous fault.
As previously stated RCDs are sensitive devices, and in order to maintain their functionality all RCDs should be tested every quarter. This involves pressing the test button (“T”) on the RCD. This process will disconnect the power supply and test the RCDs correct mechanical operation. Again quite inconvenient and because of this rarely actioned. Which leaves many installed RCDs potentially faulty and may not function correctly when truly needed. With an Autotest ARD, this problem again is resolved. The Autotest ARD, will test the RCD monthly...all on its own. No need for someone to manually push the (“T”) button. Even more importantly due to its innovative design, Power is maintained throughout the self-test process as the Autotest ARD cleverly diverts the load through its internal bypass contacts, the amazing test process only takes 7 seconds.
What are the main applications for these devices?
It’s fair to say that the applications that can benefit from ARDs are endless. Just a few examples could be:
Telecoms industry
- Street Furniture – for example signage, traffic signals, and lighting
- ATMs
- Temperature controlled environments – for example, refrigeration units, chicken farms, fish farms etc
In fact anywhere where a constant power supply is crucial to its operation. The innovation of ARDs will ultimately replace yesterdays RCD. Potentially where there is an RCD there is now the possibility, which rightly deserves great consideration to upgrade to a self sufficient ARD RCD.
Are there any standards relating to ARDs?
By seeing new technology enter to the electrical industry, the innovative devices come complete with new European standards.
The European Norm EN 50557 was finalised in 2011 and covers:
Requirements for automatic reclosing devices (ARDs) for circuit breakers-RCBOs-RCCBs for household and similar uses.
Sections can also be found in (Chapter 53) BS 7671
How is an ARD constructed? And how does it work?
ARDs can either be pre assembled devices, for example reclosing devices pre coupled with RCDs or RCBOs. They are also available in modular form, this extends the possibilities as separate devices can then be combined. A reclosing device can simply be paired with relevant, compatible RCDs or RCBOs, meeting the requirements for the many possible situations.
ARDs do not affect the normal operating functions of RCDs, they purely enhance them as they can then reclose devices that are safe to be reset. To do so, and to determine if safe or not, the device performs a circuit test, following the test, if the outcome is within the pre-determined reclosing thresholds, the device simply recloses. Importantly if unsafe the device will block and will then require manual re-closure once the fault has been removed/cleared. Gewiss have pro versions that monitor the devices status every two minutes, so if the fault clears and it is then safe to reclose, power is safely restored as and when possible.
What solutions does Gewiss offer in this area?
Gewiss is proud to be the inventor and market leader for ARD RCDs and hold worldwide patents.
Gewiss have an extensive range of devices known as ReStart and ReStart Autotest, with different configurations to suit many applications.
We can offer demonstrations of the technology on site or at our Head Office in Cambridge.