Defaulting to 24 V is habit, but as the run gets long, 24 V drop eats the LED voltage window: the far end dims or drops out. 48 V halves the current for the same power, cutting the drop to a quarter, so the same wire reaches about four times the distance. This guide gives the crossover-distance formula with a 200 W, 2.5 sq mm example, an end-voltage curve, and a selection checklist - and 48 V still sits inside SELV (under 60 V), adding no extra shock-protection requirement.
Defaulting to 24 V is habit, but as the run gets long, 24 V drop quietly eats the LED voltage window: the far end dims, colour shifts, and at worst drops out. Many people size by "24 V feels enough" and then debug the driver when the real cause is the cable. This guide turns it into arithmetic - the crossover distance.
The one-sentence rule
For the same power, 48 V carries half the current of 24 V, so the line drop (I squared R) is one quarter
The 48 V system also has twice the drop budget of 24 V (both at 10 percent), so stacked together the same wire reaches about four times the distance on 48 V
But 48 V luminaires and modules are less common than 24 V, and 48 V drivers and local buck cost more - short runs and existing 24 V loads stay 24 V; long runs, distributed layouts and 48 V-native loads go 48 V
The key premise: 48 V is still below the 60 V SELV (Safety Extra-Low Voltage) ceiling, so it adds no extra shock-protection requirement versus 24 V - that is what makes it viable for long distribution
Why 48 V wins on long runs
Drop formula: ΔV = I x R, where R = 2 x L x ρ / A (both wires)
24 V: I_24 = P / 24; 48 V: I_48 = P / 48 = I_24 / 2
ΔV_48 = I_48 x R = ΔV_24 / 2
Drop budget: 24 V at 10 percent = 2.4 V; 48 V at 10 percent = 4.8 V
Distance L scales with budget and inversely with current, so L_48 / L_24 = (4.8 / I_48) / (2.4 / I_24) = 2 x (I_24 / I_48) = 2 x 2 = 4
The "four times" assumes both systems budget 10 percent of their own voltage, use the same wire and the same load. Change the wire or the budget ratio and the number moves, but the direction - 48 V wins at distance - does not.
Worked example (200 W, 2.5 sq mm copper, ρ = 0.0172 ohm mm2 per m)
24 V drop per metre = 8.33 x 2 x 0.0172 / 2.5 = 0.1146 V/m
48 V drop per metre = 4.17 x 0.01376 = 0.0574 V/m
24 V reaches its 10 percent budget (2.4 V) at L = 2.4 / 0.1146 = 20.9 m
48 V reaches its 10 percent budget (4.8 V) at L = 4.8 / 0.0574 = 83.6 m
Same wire: 48 V reaches about 84 m, 24 V only about 21 m - almost exactly four times. At 21 m the 24 V rail is already at its floor while the 48 V end still reads 46.8 V, well inside its budget.
48 V is not brighter; on the same wire it halves the current and doubles the budget, so it reaches further
When to switch to 48 V (decision list)
Run distance exceeds the crossover distance (21 m is the 24 V boundary in the example)
The site already has or can take 48 V-native luminaires or modules, or you will add local DC-DC buck at the end
You want to shrink the wire and save copper: at the same distance 48 V can use thinner wire (next section)
The trunk is long distribution with many branches, where central supply pays off
48 V also lets you drop a wire size
In the example, 24 V needs 2.5 sq mm to reach 21 m. On 48 V the same 2.5 sq mm reaches 84 m, or at the same 21 m, 48 V needs only 1.5 sq mm (drop halves, then margin doubles again). One wire size down cuts copper cost, conduit fill and weight - that is the real saving 48 V brings to a job.
Pick 48 V to reach further or use thinner wire, not to be brighter. Short runs on existing 24 V strip forced onto 48 V only add buck cost and compatibility risk.
Five field mistakes
Blind 24 V on long runs: far-end drop exceeds limit, uneven brightness, dropouts, misread as a driver fault
Thinking 48 V is more dangerous: below 60 V SELV, no extra shock protection versus 24 V
Ignoring whether the load supports 48 V: 24 V strip on 48 V overvolts and damages it
Comparing voltage but not wire: 48 V pays off in distance or wire size, not brightness
Loosening the budget to 20 percent: the LED still cuts off at its low end and drops out
Acceptance checklist
Compute load current: 24 V uses P / 24, 48 V uses P / 48
Compute drop from wire and distance: ΔV = I x 2 x L x ρ / A, confirm at or below 10 percent
Check the LED or module minimum voltage: end voltage must be at or above it or it drops out
Beyond the crossover distance, switch to 48 V or enlarge the wire (crossover from the formula)
Confirm the load supports the chosen voltage: only 48 V loads go on a 48 V system
On 48 V, check total trunk current and pick a matching constant-voltage unit without overloading one
The 10 percent budget, copper resistivity 0.0172 ohm mm2 per m and the 60 V SELV ceiling are common values; the real budget comes from the LED minimum voltage, and voltage classes and distribution safety must follow local rules and the latest requirements of the certifying body.
Send us the load power, run distance and existing wire size. We will use the crossover formula to tell you 24 V or 48 V, how many wire sizes you can drop, and suggest a matching constant-voltage model. Contact →