Landscape Lighting Inrush Current & Peak Load Data

Four Different “Peak Load” Events Are Commonly Confused

Waveform Fingerprints: How to Tell the Startup Mechanisms Apart

LED capacitor-charging pulse

The classic electronic-load pulse is narrow and tall. It often occurs near an AC-voltage crest because the rectified input must exceed the capacitor's existing voltage before charging current flows. Two drivers with the same running wattage can have very different peaks because one includes an inrush limiter and the other does not.

Halogen cold-filament surge

The halogen waveform is broader. Current begins high because the cold filament resistance is low, then decays as the tungsten reaches operating temperature. This event carries more startup energy than a very narrow capacitor pulse even when its peak amperage is lower.

Magnetic-transformer energization

Transformer inrush can be asymmetrical and can persist for multiple AC cycles. The worst event depends on the point of switching and residual magnetic flux, which explains why the same transformer may start normally nine times and trip a breaker on the tenth.

Driver retry train

A repeated sequence of pulses often indicates that the supply voltage collapses, the driver reaches protection, shuts down and tries again. This is common at the end of a long cable or behind a high-resistance connector.

This simple peak-VA number is useful for comparison, but it is not true continuous VA and should never be used as though the peak lasts indefinitely.

Why Fixture Wattage Does Not Predict Inrush

A five-watt LED lamp can produce a greater instantaneous current peak than a ten-watt lamp if its driver has a larger input capacitor and less current limiting. Conversely, a better-designed high-power driver can have a lower controlled peak than a small inexpensive driver.

Field Measurement Protocol for Landscape Lighting Startup Current

1. Define the measurement point. Decide whether you are measuring the 120V transformer primary, low-voltage secondary, one fixture lead or a complete branch.
2. Use sufficient bandwidth. A current probe and oscilloscope or a power analyzer with peak capture is preferred. Ordinary clamp meters often average away the event.
3. Capture voltage and current together. Current without voltage cannot show whether the supply collapsed during the pulse.
4. Repeat multiple starts. Transformer energization varies with phase angle and residual core flux. One capture is not the worst case.
5. Record temperature and restart interval. A driver restarted after two seconds may behave differently from a driver that has been off for ten minutes.
6. Record load composition. List exact lamp types, fixture count, cable length, transformer tap and all switching devices.
7. Separate pulse height from pulse energy. Save peak current, pulse width and waveform shape rather than one “max amps” number.
8. Test at the symptom location. If far fixtures fail to start, measure at the end of the run under load, not only at the transformer.

Landscape Transformer Peak-Load Planning Logic

Transformer sizing should still begin with continuous connected watts and the manufacturer's loading rules. Inrush analysis is an additional reliability layer, not a replacement for standard load calculations.

1. Calculate continuous load. Add actual fixture watts, not old incandescent-equivalent labels.
2. Confirm transformer operating range. Respect minimum load, maximum load and tap instructions.
3. Classify the load mix. Separate halogen lamps, simple LED lamps, integrated fixtures and electronic accessories.
4. Identify the switching bottleneck. The weakest component may be the breaker, photocell, timer relay, smart switch or transformer thermal protector.
5. Apply startup diversity realistically. One transformer switch normally starts the whole secondary at once, so assuming random fixture startup can be unsafe.
6. Check far-end voltage during startup. A system can have acceptable steady voltage yet collapse during driver charging.

For continuous-load sizing and tap selection, use the Portfolio Lighting transformer master guide. For cable resistance and end-of-run behavior, use the landscape lighting voltage-drop calculator.

Why Mixed LED and Halogen Systems Can Be Harder to Predict

A mixed system combines two different startup envelopes. Halogen lamps create a broad cold-filament surge, while LED drivers can create narrow capacitor-charging peaks. If both events overlap, the transformer and switch see a compound waveform that cannot be predicted from either load type alone.

Mixed systems can also hide voltage problems. The halogen lamps may glow dimly during a voltage sag while an LED driver shuts off completely, making the LEDs appear defective even though both loads are experiencing the same supply event.

Breaker, Fuse and Relay Limits Are Not the Same

A breaker may tolerate a high narrow pulse that damages a small relay contact over thousands of cycles. A fuse may survive one startup but age from repeated I²t stress. A smart switch may have an LED-driver count limit that is far lower than its printed steady-state watt rating.

Source and Methodology Notes

This page separates three classes of information:

• Standardized measurement concepts: peak current, pulse duration, waveform capture and multiple-unit analysis are consistent with the purpose of IEC 63129, which defines a method for determining inrush characteristics of lighting products.
• Manufacturer evidence: published LED-driver and luminaire specifications demonstrate that inrush can be many times steady input current and that unit-count limits may be specified separately for different breaker curves.
• PortfolioLighting.net planning ranges: the category multipliers in this database are conservative field-screening ranges. They are not copied product ratings and must not replace exact manufacturer data.

IEC 63129 was amended in 2025. This database therefore records waveform context instead of relying on an unqualified “amps at startup” figure.