Inrush current: The impact on LED dimming

Inrush current: The impact on LED dimming

LED lighting is the go-to for many electrical installations, due to the longer lifespan, energy efficiency and design flexibility. However, when installing LEDs, many situations arise where large inrush currents can cause damage to lighting control. Inrush can be unpredictable, and slightly tricky to get your head around, so let us talk you through it.

What is inrush current?

Inrush current is the surge of energy, required by all fittings and drivers, when you first turn them on. Much like any other power supply, an LED’s internal capacitors charge up in less than a millisecond once turned on. The speed of this can cause such a large inrush current which can be about 6 times higher than a traditional incandescent lamp.

What problems can it create?

When dimming loads, you’re also tasked with trying to control the inrush current. The high inrush current caused by LEDs can trip fuses, damage circuit breakers and cause dimmer failure - if a fuse trips regularly when switched on, you can bet the inrush current is to blame. With parallel connections, the inrush current adds up and is more likely to cause issues than with an individual light source. 

It can also affect the light switch internally due to mechanical damage, causing sparking or crackling and a very similar impact can be had on a relay, used frequently in modern lighting.

How can I combat this?

For initial prevention, you can use circuit breakers, although we see many of these fail. Circuit breakers have the potential to trip when the current is around 5 to 10 times its rating, which can happen more often than you’d think. 

Some manufacturers will give an indication of the internal resistance on their data sheets, but this value is often missing, making it harder to calculate. On the first approach, multiply by the industry standard of ‘1.8’, to get a more realistic idea of the inrush current. 

Another approach would be to opt for high-quality products. Manufacturers who use things like high-quality relays and use a rigorous testing process are more likely to meet the currents written on their data sheets. Without an efficient testing process, the currents can be unpredictable. At Zano, we actually offer free lamp testing, which could save you a few back and forths to your local wholesaler.

Similarly to this rigorous testing, all of Zano’s dimmers have Learn & Adapt technology, which means they quite literally learn and adapt to the inrush current. This can help you control the current, ultimately supporting a greater number of lamps per circuit.


Remember, if you’re ever unsure about inrush, Zano Controls’ lamp testing is available to all, alongside our technical helpline. Just give us a call on 0345 519 5858 and we’ll get #TeamZano on the job.

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