A driver marked 100 to 277 V does not behave the same across the whole span. The lower end is an undervoltage cutoff, the upper end an overvoltage trip, and input current rises as voltage falls - so the AC breaker and cable must be sized on the lowest input voltage, not the nameplate rating. This guide gives the window diagram, the input-current formula with a 100 W example, failure modes at each end, and a checklist.
A driver marked 100 to 277 V does not behave the same across the whole span. The wide range only means it works between the two ends, and those ends are protection thresholds, not a comfort zone you can use carelessly. Drop below the floor and it shuts down; exceed the ceiling and overvoltage protection trips; and the closer you sit to either end, the less voltage margin the internal parts have.
The one-sentence rule
Floor = undervoltage cutoff: below it the driver stops or restarts repeatedly, not just "runs a bit less efficiently"
Ceiling = overvoltage trip: above it protection acts; wrong voltage can latch it off or blow the fuse
The part everyone misses: because output power P is about input voltage times input current times efficiency, lower input voltage means higher input current - so the AC breaker and cable must be sized on the lowest input voltage, not the nameplate or the mid value
What the window frames
Supply on site
Nominal
Where it sits in 100 to 277 V
Watch out
North America 120 V branch
120 V
Inside, about 20 V (16.7 percent) headroom at the low end
OK, but count long-cable drop
Europe / China 230 V
230 V
Middle of the band, plenty of margin
Most forgiving
North America 277 V branch
277 V
Right at the ceiling, sags trip it
Only about 7 percent margin; confirm ceiling is 277 V or higher
90 to 305 V unit
Wider cover
277 V still leaves about 28 V margin
Suits volatile grids and generators
The grid itself swings about plus or minus 10 percent. A unit whose ceiling is 277 V will trip its overvoltage protection on a 277 V branch whenever the voltage runs high - that is the window hitting its top, not a faulty driver.
Lower input voltage means higher AC current (the part most often missed)
Input current formula:
I_in = P_out / (V_in x PF x efficiency)
P_out driver output power (W)
V_in actual input voltage (V)
PF power factor, typically 0.9 to 0.95
efficiency typically 0.85 to 0.9
Worked example: a 100 W driver, PF 0.95, efficiency 0.9
At 277 V in: I = 100 / (277 x 0.95 x 0.9) = 0.42 A
At 100 V in: I = 100 / (100 x 0.95 x 0.9) = 1.17 A
The low-voltage input current is 2.8 times the high-voltage one. Size a 1 A breaker from the 0.42 A at 277 V and it will overload on a 100 V site. So the breaker and cable are always sized on the lowest input voltage, then given 1.25 times headroom (the method is in how many drivers per circuit).
Same window, generous at 230 V, at the ceiling on a 277 V branch - wide input is not stable everywhere
Failure modes at each end
Direction
What triggers it
What you see on site
How to confirm
Below floor (undervoltage)
Grid sag, generator start, long AC drop
Restarts repeatedly, flickers, hard to start cold
Measure input; below the nameplate floor confirms it
Order: confirm the site voltage sits in the window including plus or minus 10 percent, then compute AC current at the lowest input voltage, then size the breaker and cable. Size from the mid value and low-voltage or generator sites will fail.
Five field mistakes
Sizing the breaker from the nameplate rating: mid-value 230 V gives 0.5 A, but the site runs 1.17 A and overloads
Putting a 100 to 240 V unit on a 277 V branch: overvoltage protection trips, looks like a driver fault
Assuming wide input ignores grid swing: add plus or minus 10 percent and a 277 V unit tops out on a 305 V grid too
Long AC cable drags the input under the floor: still lit but undervoltage, driver restarts
Watching only the ceiling: solar and generator start voltages run low, cold start is hard, misread as a fault
Acceptance checklist
Measure the open-circuit supply voltage: inside the window, with plus or minus 10 percent included
Compute input current at the lowest input voltage: I = P / (V_min x PF x efficiency)
Breaker at 1.25 times that current: the low-voltage current is the basis, not the mid value
The PF 0.95, efficiency 0.9 and plus or minus 10 percent grid swing are typical orders of magnitude; take the real values from the driver datasheet and local grid rules. Any change to distribution or earthing must follow local rules and the latest requirements of the certifying body.
Send us the supply voltage range, load power and whether you run long cables. We will check whether the nameplate window covers it, which input current to size the AC breaker and cable on, and suggest a matching wide-input model. Contact →