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What are the issues of inrush current, and how to fix it

5 September 2022

Even though inrush currents may only last for a few microseconds, it might take a few seconds for the current to stabilize to the average operating value. The high level of currents may produce voltage dips, a product of current and installation impedance.

Inrush current is the instantaneous high input current drawn by a power supply or electrical equipment at turn-on. At turn-on, the discharged capacitors in power supplies offer low impedance allowing high current to flow into the circuit as they charge from zero to their operational values. These currents can be many times higher than the steady state currents. If your equipment is compliant with EU standards and your installation is correctly dimensioned, these voltage dips are harmless. According to standards (IEC 61547) products need to withstand a certain amount of voltage dips without malfunction.


So, why is Inrush current an issue?

If you experience malfunctions, this could be a sign that your products are not compliant with standards or the dimensioning of the installation is incorrect. Inrush may be an issue when dimensioning your installation. Your target is to obtain a technically permissible combination together with an economically efficient overall system. When upgrading an existing installation, the number of devices the single circuit can operate could be limited, and you might need to increase the number of circuits. This means more working hours and materials that will add to your budget.

If, for example, you have an installation with 27 W luminaires with a traditional driver with a limit of e.g: 23 luminaires, a 10 A fuse C-characteristic, the fuse will only be loaded with 27% of the fuse’s rated current”, says Henrik and continues: “If you want to limit the fuse load to 80%, there is thus 53% free capacity in the fuse, which can be utilized if you choose a driver without starting current”.

An example of the potential installation savings can be seen in the table.

Selecting a LED driver with a low inrush current can help you save time, money, and materials, according to Thomas Andersen, Lead R&D Engineer & Co-founder of Nordic Power Converters: “As I see it there are two obvious reasons. For new installations, it’s about savings. Less inrush current requires fewer main circuit breakers, less cabling, and therefore fewer electrician hours, you do the math. For already existing installations you can simply have more LED drivers connected, that gives the architect or the designer more freedom”.


Lack of space for electrical installations  

When building new commercial properties, you do not have to deal with legacy electrical equipment. But the lack of space for electrical installations and switchboards is a recurrent issue, says Henrik Rohde Nielsen from Light Bureau Denmark. Light Bureau is an international lighting design practice with a comprehensive portfolio of projects in workplaces, residential, hospitality, and more.

The problem in many new projects is the lack of space, says Henrik. Everything needs to be minimalistic and invisible. So we are constantly challenged with not enough cable routes for ventilation, lighting, etc.”.

And the bad news is that the more circuit breakers you need, the more space you will need for cables and switchboards. No wonder Henrik has a strong wish for luminaires with the lowest possible inrush. Luminaires with low inrush are something that Erik Padkjær Larsen feels strongly about. Erik is a designer with here&after who designs, develops, and engineers customized lighting solutions, and he is a strong advocate of practical, well-engineered design that achieves more with less.

The challenges with inrush are many, says Erik. Say you have an installation with 100 LED luminaires you would probably need three circuits if they have a high level of inrush, which is often the case if the LED driver is selected without focus on inrush. By choosing luminaires with low inrush, you can have them all on the same circuit. Hence three times less cabling and three times fewer work hours spend on the installation. That is an important reduction in time and money for the installer. The client will experience the benefits in both short and long term as the installation will have higher reliability and maintenance will eventually be more cost-effective”.


Sustainable solutions

Time and money are definitely critical, but the environment is equally important to Henrik and Erik.

Using fewer components obviously reduces the cost of installation, and maintenance says, Henrik. But it is equally important to mention that reducing the amount of material is a huge benefit for the environment. At Light Bureau, we are committed to accelerating the transition toward a more sustainable society. Early on in the project, we will engage in a conversation with the property developer about sustainability and their ambitions towards sustainability. And we always try to push them towards the more sustainable solutions”.


So, which solutions are available in the market today?  

Using inrush current limiters is an option, says Henrik. We have used inrush current limiters as part of some lighting installations, including the one on the Øresund Bridge pylon illumination. Obviously, the device is an added cost, but the savings in cable and work hours easily makes up for that cost”. The lighting system on the Øresund Bridge was built with 192 LED RGBW luminaires and for every four luminaires is an inrush current limiter. This optimized system will reduce consumption and create considerable energy savings of up to 80% compared to the old lighting system.

At here&after they value design, quality, and efficiency, says Erik. “We want to make it easy for the end-user and the installer. The end-user wants beautiful design, great quality of light, and a reliable and energy-efficient light system. The installer wants plug-and-play solutions that are easy to implement. That is one of the reasons we use InviTrack LED drivers in our luminaires. The driver is miniaturized and completely invisible. It is slightly more expensive than other drivers on the market but the benefits and the time saved on installation easily compensate for that extra cost”.

InviTrack drivers have negligible inrush. That means you can considerably reduce the number of circuit breakers and the cabling. With fewer components in a system, you will not only reduce the amount of time spent on the installation but also the time you spend on future maintenance. According to Thomas, there is a simple reason for selecting a LED driver from NPC: “If you want to bring down the total system cost, you consider the sum of expenses; MCBs, cables, installation, drivers and future maintenance. The LED driver of choice has a significant impact on the cost of all other aspects of your system cost. Going too cheap on the driver gives you less profit down the road. Drivers from NPC have for instance very low inrush current and suddenly you save on the amount of MCBs, cabling, and the cost for your electrician team. Quality and lifetime are other features of NPC LED drivers which will reduce your bill in future maintenance, but that’s another story for another time”.

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