Calculate the combined peak inrush current of LED drivers switched together, or estimate how many drivers fit on an MCB from datasheet and load limits.

Optional settings
T50 from the driver datasheet. Blank skips the I²t estimate.

LED Inrush Current Formula

The following equation is used to estimate the total peak inrush current when multiple identical LED drivers energize at the same time.

Iₜotal = Iᵢnrush,driver × D
  • Where Itotal is the total peak inrush current (A)
  • Iinrush,driver is the peak inrush current of one LED driver at turn-on (A), typically taken from the driver datasheet for a stated line voltage and pulse width
  • D is the number of drivers that energize simultaneously

To estimate total inrush current, multiply the driver’s specified peak inrush current by the number of drivers switching on at the same time. This is a worst-case approximation; real installations can differ due to wiring impedance, phase angle, and any inrush limiting.

What is LED Inrush Current?

Definition:

In LED lighting systems, inrush current usually refers to the brief surge of input current drawn by the LED driver/power supply when AC power is first applied. It is primarily caused by charging the driver’s input capacitors (and, in some designs, transformer magnetizing current). The surge is typically very short (often microseconds to a few milliseconds) but can reach tens of amps or more.

Inrush current is not a “turn-on current” of the LED die itself in normal constant-current LED circuits; the LED current is controlled by the driver (or by a series resistor/regulator) after the supply starts up.

Because inrush can be high, it can nuisance-trip breakers, stress relays/contacts, and affect upstream power equipment. For accurate design, use the driver datasheet’s inrush specification (including pulse width and test conditions) and consider measures like staggered turn-on or inrush limiting.

How to Calculate LED Inrush Current?

For an LED driver installation, the most reliable method is to use the driver datasheet value for “inrush current” (often given as a peak current and a pulse width at a specified line voltage), then estimate the combined inrush.

Steps:

1) Find the driver’s peak inrush current rating (example: 30 A peak for 200 µs at 230 VAC).
2) Multiply by the number of drivers that may turn on at the same time.
3) Use the applicable driver and protective-device manufacturer guidance, including pulse duration, waveform and installation conditions. A peak value alone does not establish breaker compatibility.

Example (worst-case): If one driver has a 30 A peak inrush rating and 8 drivers energize simultaneously, the estimated total peak inrush is 30 A × 8 = 240 A.

Note: Actual inrush is strongly affected by installation conditions (line impedance, cable length, temperature, inrush limiting components, and the exact switch-on phase angle). When sizing protection devices, consult applicable standards and manufacturer guidance. The optional I²t estimate uses Signify’s Ipeak² × 0.8 × T50 convention from melting-fuse guidance; it is not a universal MCB trip test. The Drivers per circuit breaker (MCB) mode requires the same driver’s datasheet count on a 16 A Type B MCB and a compatible conversion percentage. The smaller of the rounded-down manufacturer count and the entered steady-load limit is reported as a planning estimate, not a certified safe capacity.