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g/electrical • Posted by u/sparky420 •

277V LED drivers tripping breaker on cold start — inrush current issue?

Running into intermittent startup failures on a commercial install. 40x Meanwell HLG-240H-C700B LED drivers on a single 20A circuit at 277V.

Panel schedule shows Circuit 14 — all drivers wired parallel on 12AWG to a Square D QO220 breaker. Trips about 1 out of every 5 cold starts, always in the first 500ms. Hot starts are fine.

My suspicion is inrush, but I did the math and I'm embarrassed it took me this long:

Each driver draws ~0.9A at 277V. 40 × 0.9A = 36A continuous.

I've been running at 180% capacity. The cold-start trips might actually be saving my wiring. Do I split this into two circuits minimum, or am I missing something?

💬 4 replies

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u/admin_jake ADMIN •

Your math is correct and that's the whole problem. 36A continuous on a 20A breaker is a fire waiting to happen. Inrush is a separate problem on top of the overload — Meanwell specifies "Typical 100A for 200µs" per driver at 277VAC. You're asking one breaker to handle 4000A peak then settle at 180% rated capacity. Split into three circuits minimum, 15A each.

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u/conduit_king •

Had almost the same thing at a warehouse job. 30 drivers on a 20A circuit, client wondering why the breaker kept tripping "randomly." Split to two circuits, never tripped again. Don't overthink it — you found the problem, now fix it.

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u/nec_nerd •

NEC 210.20(A) — branch circuit rating must not be less than the load. Continuous loads (3+ hours) require 125% sizing. 36A × 1.25 = 45A minimum breaker rating, which means your minimum would be two 25A or 30A circuits. Three 20A circuits gives you headroom. Get this corrected before the AHJ sees it.

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u/voltage_vince •

If you absolutely can't add circuits, inrush limiters (NTCs) can soften the startup spike, but that doesn't fix the continuous overload. That's the real issue. Inrush limiters are a band-aid here.

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