Hvad er Spændingsfald-regnemaskine?
spænding drop er the reduction i electrical potentiale den happens whenever current flows gennem the modstand af en wire. Den er unavoidable — hver conductor, nej matter hvordan good, har nogle modstand — men det becomes en real problem når en cable køre er long, the conductor er undersized, eller the load current er high. Left unchecked, excessive spænding drop årsager motors til køre hot og tabe moment, lights til dim eller flicker, og electronic equipment til behave unpredictably eller fail early.
Denne beregner uses the standard electrician's spænding-drop formel based på conductor resistivity, cable length, cross-sectional area, og load current. Den supports begge single-phase (out-and-back) og three-phase (√3) wiring, og begge copper og aluminum conductors, so det works for household wiring, industrial feeders, solar installations, og long outdoor eller underground cable runs anywhere i the world — the formel er purely physical og gør ikke depend på enhver single country's electrical code.
Trin:
- Vælg system type: single-phase for fleste household og small commercial circuits, eller three-phase for larger motors og industrial feeders.
- Vælg den conductor material — copper or aluminum — since aluminum has significantly higher modstand for the same size
- Indtast supply spænding i volts og the load current i amps den the circuit vil actually carry.
- Indtast one-way cable length i meter (measure the physical køre fra source til load, ikke there-and-back).
- Indtast the conductor's cross-sectional area in mm² (Tjek cable's printed size or a wire gauge chart).
- Read the spænding drop, drop procentdel, spænding delivered til the load, og the maksimum cable length den keeps du under the 3% guideline.
Formel
Enkeltfase: Vdrop = (2 × ρ × L × I) / A
Trefase: Vdrop = (√3 × ρ × L × I) / A
Hvor:
ρ = Resistivitet (Ω·mm²/m)
L = Ledningslængde (m)
I = Strøm (A)
A = Lednings tværsnitsareal (mm²)
Spændingsfald % = (Vdrop / Fasespænding) × 100
Anvendelsessager
- Sizing cable runs for household sub-panels, workshops, og outbuildings
- Tjekker solar panel og battery wiring for excessive line tab over long DC eller AC runs
- Verifying motor feeder cables in industrial og commercial three-phase installations
- Planning extension cords eller temporary kraft runs for construction sites og events
- Diagnosing dimming lights eller underperforming appliances at the end of a lang circuit
Nøglefordele
- Instantly compares single-phase og three-phase wiring uden redoing the math by hand
- Shows begge the raw spænding drop og the procentdel imod din supply spænding side ved side
- beregnes the maksimum cable length den stays within the standard 3% guideline
- Works med enhver currency og enhver country's supply spænding — the physics doesn't ændre
- Copper vs. aluminum comparison helps you decide hvis upsizing the leder eller switching material is mere omkostning-effective
Pro tips
- As en rule af thumb, holde spænding drop under 3% for branch circuits og under 5% for the total feeder-plus-branch run.
- If en køre er borderline, det er sædvanligvis cheaper til gå op one standard conductor size than til redesign the circuit path.
- For lang DC solar eller battery runs, spændingsfald matters even mere — reberegne using your actual system spænding, ikke 230V eller 120V.
- Keep en note af the maksimum recommended length shown here når planning future extensions til the same circuit.
Almindelige fejl at undgå
- Entering the round-trip cable length instead af the one-way distance — the formel allerede accounts for the afkast path.
- Mixing op AWG og mm² conductor sizes, hvilken produces en spænding drop den er af ved en large margin.
- Ignoring three-phase loads og altid using the single-phase (×2) formel, hvilken overstates the real drop ved omtrent 15%.
- Forgetting den aluminum conductors behøve en larger cross-sectional area than copper til carry the same current med the same drop.
Nøglebegreber forklaret
- spænding drop: The tab of electrical potential across a conductor caused by its modstand, measured in volts.
- Resistivity: A material property describing hvordan strongly a leder resists strøm flow, measured in Ω·mm²/m.
- Cross-sectional areal: The thickness of the leder's copper eller aluminum core, measured in mm², ikke counting insulation.
- Tre-phase factor (√3): The multiplier used instead of 2 for Saldod three-phase circuits, reflecting the 120° phase relationship between conductors.
Eksempel
En enkeltfase 230V-kreds forsyner en 16A-belastning gennem et 2,5 mm² kobberkabel på 25 meter enkeltvejs. Spændingsfald = (2 × 0,0172 × 25 × 16) / 2,5 ≈ 5,5 V, hvilket er ca. 2,4% af 230V — komfortabelt inden for 3%-retningslinjen, og belastningen modtager faktisk ca. 224,5V.