Select a relay for LED drivers using the contact’s applicable lighting-load and making-current evidence, not its resistive ampere rating alone. Check steady current, inrush waveform, switching frequency, and electrical endurance for the actual driver group. A 10 A resistive marking does not establish how many capacitive-input LED drivers the contacts can repeatedly switch.
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LED driver inrush current sets a different relay requirement from the running RMS current. For lighting OEMs, this guide addresses the relay or contactor contacts: applicable making-current limits, switching duty, and electrical endurance. Use the guide to starting multiple power supplies for upstream branch-protection coordination and staged AC energization. A driver count permitted by a breaker table does not qualify a relay contact switching that group.
Define what the contacts switch
Start with a circuit drawing. Are the contacts switching AC power into several drivers, switching a permitted DC load, or operating a control input? Those duties cannot share one current calculation. This article’s worked example concerns a single AC contact supplying a group of LED drivers.
Identify the supply voltage and frequency, number of drivers per contact, normally open or normally closed contact, and expected switching schedule. Include any socket, PCB track, plug, and enclosure temperature limits. A suitable relay element does not automatically qualify its complete mounting assembly.
A driver’s input capacitor can draw a short charging pulse when power is applied. The pulse depends on circuit design and test conditions. The referenced explanation of load types distinguishes resistive loads from lamp and capacitor loads with substantial inrush. Its illustrative load ratios are not a substitute for the selected driver’s waveform.
Read the correct contact ratings
The useful question is whether the manufacturer rates the exact contact version for the required load and life. A maximum switching current, continuous carrying current, or mechanical-life figure may describe a different duty from repeatedly closing onto a driver input.
The external relay technical guide, contact specification and AC1 sections separates AC1 resistive duty, lamp ratings, peak current, and inrush-specific energy. Read their conditions together. A brief peak-current capability is not permission to carry that current continuously, and an AC1 endurance curve does not establish LED-load endurance.
| Entry | Useful for | Does not establish by itself |
|---|---|---|
| AC resistive / AC1 rating | Specified resistive switching duty | Driver-bank making capability |
| LED or lamp rating | The stated lighting duty and conditions | Every driver topology and pulse shape |
| Peak current and pulse conditions | Short-duration making screen | Continuous thermal capacity or service life |
| Electrical endurance | Life under the stated load and cadence | The same life with a different load |
Screen an eight-driver example
The efficiency and power-factor input-current method applies to running demand; it does not calculate the making-current waveform.
Hypothetical example, not WEHO measured data: eight identical drivers each supply 40 W. Assume 90% efficiency and 0.90 true power factor at 230 V AC under the condition being evaluated. Estimated group real input power = 8 × 40 W ÷ 0.90 = 355.6 W. Estimated RMS input current = 355.6 W ÷ (230 V × 0.90) = 1.72 A.
For a separate illustrative making-current screen, assume each driver has a 12 A peak charging pulse under the same defined supply condition. If all eight identical pulses overlapped without supply limitation, their arithmetic peak sum would be 96 A. Actual group current must be established for the installation; source impedance and pulse timing can change it.
| item | Calculation or input | Meaning |
|---|---|---|
| Lakas ng output | 8 × 40 W = 320 W | Load delivered by the drivers |
| Estimated steady input current | 320 ÷ 0.90 ÷ 230 ÷ 0.90 = 1.72 A | Preliminary thermal and running-duty input |
| Illustrative overlapping peak | 8 × 12 A = 96 A | Prompt to examine making capability |
| Pulse width and waveform | Not supplied in this example | Prevents a final contact-selection conclusion |
The 1.72 A estimate could look comfortable against a hypothetical 10 A resistive marking, while leaving the making duty unresolved. Neither 10 A ÷ 12 A nor 96 A ÷ 10 A produces an allowable driver count. The numerator and denominator describe different duties. Obtain compatible waveform and contact evidence before approving the bank.
Review the making-current waveform
Request peak current with its input voltage, temperature, initial capacitor condition, source conditions, and pulse-width definition. A half-peak width and a total pulse duration are different quantities. Two pulses with the same maximum amplitude can impose different thermal stress and contact behavior.
A specific document starting point is the XLG-100 product page: XLG-100-24 variant and XLG-100 datasheet (PDF), which provide a stated cold-start current condition. Obtain the pulse waveform, duration, restart conditions, and relay evidence for the exact variant used. This 100 W product is separate from the hypothetical 40 W/12 A drivers in the example above; those numbers must not be transferred to it.
Where the contact manufacturer provides an applicable I²t criterion, use the integral of the actual current squared over the specified interval. The expression is I²t = ∫i(t)² dt. Peak current squared multiplied by duration is only a rectangular-pulse approximation; peak current multiplied by duration has different units and is not I²t. An I²t comparison also does not replace the peak-current limit, electrical endurance, bounce behavior, or the manufacturer’s stated test conditions.
A published maximum number of drivers on a circuit breaker answers a different coordination question. It does not certify a relay between that breaker and the drivers. Obtain the relay manufacturer’s LED-load table, compatibility statement, or an agreed qualification procedure for the complete driver group.
Specify switching life and recovery time
A relay making one lighting transition each day has a different duty from a contact repeatedly following an occupancy signal. Define required switching operations, minimum on-time and off-time, and credible control faults. State how quickly the driver can be re-energized; an inrush limiter’s condition after a brief interruption may differ from a cold start.
Do not solve uncertainty by paralleling relay contacts unless the manufacturer explicitly permits the arrangement for that load. Unequal closing times and contact resistance can prevent equal sharing. Likewise, a larger relay or a contactor still needs evidence for its lighting duty. A different switching architecture can be evaluated, but its suitability must be established on its own terms.
Coil suppression is another independent check. Use the control device’s and relay manufacturer’s instructions, and account for any change in release time. A suppression component added across the contacts can create an off-state current path; evaluate unwanted glow, discharge, and the resulting switching duty rather than assuming suppression is always beneficial.
Qualify the production combination
Qualification should use the intended relay variant, contact material, socket, driver revisions, cable layout, supply conditions, and enclosure temperature. Measure with equipment capable of capturing the pulse without clipping. A small displayed peak is uninformative if the probe or acquisition system has saturated.
| Condition | Record | Evaluate |
|---|---|---|
| Cold energization | Group waveform and source conditions | Applicable making limits |
| Short interruption and restart | Off-time, temperature, waveform | Recovery behavior and repeatability |
| Required switching cadence | Cycle count and contact condition | Agreed endurance criteria |
| Steady operation | RMS current and terminal temperatures | Complete assembly thermal limits |
A few successful starts are a functional observation, not a service-life result. Retain the accepted combination and its boundaries so a driver or relay substitution triggers review rather than inheriting an unsupported approval. The power-supply replacement compatibility checklist helps document those changed interfaces.
Prepare a useful driver inquiry
Contact WEHO about a relay-switched driver group through the contact form with AC supply, driver model or required output and quantity per contact, relay model if known, and switching schedule. Unknown relay details can be marked as unknown while the driver requirements are clarified.
