तारको अर्को छेउमा कति भोल्ट पुग्छ?Check voltage at the far end of a cable

तारमा कति voltage drop हुन्छ?How much voltage will your wire lose?

तारको material, size, एकतर्फी दूरी, current र phase राख्नुहोस्। यो resistance मा आधारित सुरुवाती हिसाब हो, सुरक्षित wire size को अन्तिम निर्णय होइन।Enter the wire material, cross-sectional area, one-way length, current, and phase. This is a resistance-based first estimate, not a final cable selection.

Circuit र तारको विवरणCircuit and conductor details

तारको materialConductor material

Circuit को प्रकारCircuit type

एउटा conductor को sizeArea of one conductor

mm²

Cable marking वा datasheet को mm² राख्नुहोस्।Use the mm² printed on the cable or its datasheet.

एकतर्फी cable दूरीOne-way cable length

Source बाट load सम्मको दूरी। Single-phase मा फर्किने तार tool ले आफैं जोड्छ।Distance from source to load. The tool adds the return path for a two-wire circuit.

चल्ने currentLoad current

तीन phase मा balanced line current राख्नुहोस्।For three-phase, enter the balanced line current.

Nominal circuit voltageNominal circuit voltage

तीन phase मा line-to-line voltage राख्नुहोस्।For three-phase, use line-to-line voltage.

अनुमानित conductor तापक्रमEstimated conductor temperature

°C

70°C उदाहरण मात्र हो। Cable insulation rating वा ambient temperature होइन।70°C is an example. This is conductor temperature, not the insulation rating or ambient temperature.

तपाईंको planning limitYour planning limit

3% common branch-circuit example हो। लागू हुने Nepal code र project requirement electrician ले जाँच्नुपर्छ।3% is a common branch-circuit example. An electrician must check the applicable Nepal code and project requirement.

भोल्टेज ड्रपको अनुमानVoltage-drop estimate

अनुमानित voltage dropEstimated voltage drop 5.16 V 2.24% of 230 V

Within the entered 3% planning limit.

Load मा बाँकी voltageEstimated load voltage224.84 V

तारमा power lossConductor power loss103.1 W

एकतर्फी resistanceOne-way resistance0.1289 Ω

Target भित्रको अधिकतम दूरीMax length at target33.4 m

Drop ले मागेको न्यूनतम areaMinimum area by drop only2.99 mm²

Drop मात्र हेर्दा अर्को common areaNext common area by drop only4 mm²

यो wire-size approval होइनThis does not approve a wire size

Cable को ampacity, breaker, fault current, earthing, insulation, grouping, conduit वा जमिनभित्रको installation, connection quality र local rule छुट्टै जाँच्नुपर्छ। Aluminium मा सही terminal र installation practice झन् जरुरी हुन्छ। योग्य electrician वा electrical engineer बाट design जाँच गराउनुहोस्।Cable ampacity, breaker protection, fault current, earthing, insulation, grouping, conduit or buried installation, termination quality, and local rules need separate checks. Aluminium also needs suitable terminals and installation practice. Have a qualified electrician or electrical engineer verify the design.

हिसाब कसरी हुन्छ?How the calculation works

लामो, तातो वा सानो तारको resistance बढी हुन्छ। Single-phase वा DC two-wire मा current जाने र फर्किने दुवै conductor गनिन्छ। Balanced three-phase मा √3 factor प्रयोग हुन्छ।A longer, hotter, or smaller conductor has more resistance. A single-phase or DC two-wire circuit includes both outgoing and return conductors. A balanced three-phase circuit uses the √3 factor.

ρT = ρ20 × [1 + α × (temperature − 20°C)]
one-way resistance R = ρT × length ÷ area
single-phase or DC drop = 2 × current × R
balanced three-phase drop = √3 × current × R
drop % = voltage drop ÷ nominal voltage × 100
conductor loss = 2 × I²R (two-wire) or 3 × I²R (three-phase)

Copper का लागि ρ20 = 0.017241 Ω·mm²/m र α = 0.00393/°C। Conductor-grade aluminium का लागि ρ20 = 0.028264 Ω·mm²/m र α = 0.00403/°C। वास्तविक cable resistance फरक हुन सक्छ, त्यसैले उपलब्ध भए manufacturer को Ω/km data प्रयोग गरेर engineer ले फेरि जाँच्नुपर्छ।Copper uses ρ20 = 0.017241 Ω·mm²/m and α = 0.00393/°C. Conductor-grade aluminium uses ρ20 = 0.028264 Ω·mm²/m and α = 0.00403/°C. Real cable resistance can differ, so an engineer should recheck with the manufacturer's Ω/km data when available.

नमुना हिसाबWorked example

नमुनामा 230 V single-phase circuit, 4 mm² copper, 25 m एकतर्फी दूरी, 20 A load र 70°C conductor temperature राखिएको छ। Planning limit 3% हो।The example is a 230 V single-phase circuit using 4 mm² copper over a 25 m one-way run at 20 A and an estimated 70°C conductor temperature. The entered planning limit is 3%.

0.017241 × [1 + 0.00393 × 50] = 0.020629 Ω·mm²/m70°C मा resistivityresistivity at 70°C

0.020629 × 25 ÷ 4 = 0.1289 Ωएकतर्फी conductor resistanceone-way conductor resistance

2 × 20 × 0.1289 = 5.16 Vजाने र फर्किने conductor को dropdrop across outgoing and return conductors

5.16 ÷ 230 × 100 = 2.24%राखिएको 3% limit भित्रwithin the entered 3% limit

230 − 5.16 = 224.84 Vload मा अनुमानित voltageestimated voltage at the load

2 × 20² × 0.1289 = 103.1 Wदुवै conductor मा heat lossheat loss in both conductors

स्रोत र मान्यताSources and assumptions

Nepal Department of Urban Development and Building Construction, NBC 207 Electrical Design Requirements, checked 4 Sep 2026. Nepal's public-building code requires conductor selection and electrical installation to follow the applicable wiring, rating, inspection, and safety requirements.
Government of Nepal curriculum, Basic Electrical Installation and Workshop Technology, checked 4 Sep 2026. Its NBC 207 teaching material says conductor sizing must consider both current-carrying capacity and voltage drop, which is why this page does not turn the drop result into a safety approval.
Minnesota Department of Labor and Industry, License Examination Guide, checked 4 Sep 2026. It derives approximate voltage drop from Ohm's law and uses factors 2 for single-phase and 1.732 for three-phase, while warning that reactance, power factor, harmonics, large feeders, and inductive loads need fuller analysis.
NIST Handbook 100, Copper Wire Tables, checked 4 Sep 2026. It gives standard annealed-copper resistivity as 0.017241 Ω·mm²/m at 20°C and the 0.00393/°C temperature coefficient used here.
NIST Handbook 109, Aluminum Wire Tables, checked 4 Sep 2026. It gives the conductor-grade aluminium resistivity and temperature relationship used by the estimate.
Seattle Public Utilities, Electrical Design Calculations, February 2024, checked 4 Sep 2026. Its full AC approximation includes resistance, reactance, and load power factor. Those extra terms are outside this simple resistance-only calculator.

4 mm², 25 m, 20 A, 70°C र 3% सबै उदाहरण मात्र हुन्। यो model ले conductor को DC resistance अनुमान गर्छ। AC reactance, power factor, harmonics, motor starting, unbalanced phase, joints र manufacturer tolerance समावेश छैन।The 4 mm², 25 m, 20 A, 70°C, and 3% values are examples only. This model estimates conductor DC resistance. It excludes AC reactance, power factor, harmonics, motor starting, phase imbalance, joints, and manufacturer tolerance.