Circuit Analysis calculator
Current Divider Calculator
Professional current divider calculator for electrical engineers, electronics technicians, and students. Calculates how current distributes between 2–6 parallel branches using the current divider rule. Supports amps, milliamps, and microamps. Shows individual branch currents, percentages, power dissipation per branch, and equivalent parallel resistance.
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Quick Tips
- All calculations follow NEC standards and US electrical practices
- Results update automatically as you change input values
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- Always verify results with local electrical codes
Important Disclaimer
Calculations are for reference only. Always verify against NEC and local codes before installation. Consult a qualified professional for critical applications.
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Example Calculations
Two Parallel Resistors
Basic current divider with R1=100Ω and R2=200Ω
- totalCurrent: 10
- currentUnit: A
- resistor1: 100
- resistor2: 200
How to Use
Current Divider Rule: How Current Splits in Parallel Circuits
In a parallel circuit, current divides inversely proportional to resistance — the lower resistance path carries more current. This is the opposite of a voltage divider (series circuit), where voltage drops proportionally to resistance. The current divider rule is fundamental to circuit analysis and is derived directly from Kirchhoff's Current Law (KCL) and Ohm's Law.
The Current Divider Formula
For any branch n in a parallel circuit:
I_n = I_total × (R_parallel / R_n)
Where:
- I_n = current through branch n
- I_total = total current entering the parallel network
- R_parallel = equivalent parallel resistance of all branches
- R_n = resistance of branch n
For the special case of exactly two parallel resistors, the formula simplifies to:
- I₁ = I_total × R₂ / (R₁ + R₂) — note: the "other" resistor is in the numerator
- I₂ = I_total × R₁ / (R₁ + R₂)
Worked Example: Three Parallel Resistors
Total current = 12A, R₁ = 100Ω, R₂ = 200Ω, R₃ = 300Ω
| Step | Calculation | Result |
|---|---|---|
| Parallel resistance | 1/(1/100 + 1/200 + 1/300) = 1/(0.01 + 0.005 + 0.00333) | R_p = 54.55Ω |
| I₁ (100Ω branch) | 12A × 54.55/100 | 6.55A (54.5%) |
| I₂ (200Ω branch) | 12A × 54.55/200 | 3.27A (27.3%) |
| I₃ (300Ω branch) | 12A × 54.55/300 | 2.18A (18.2%) |
| Verification (KCL) | 6.55 + 3.27 + 2.18 | = 12.00A ✓ |
The 100Ω branch (lowest resistance) carries the most current — more than half the total. This is the inverse relationship at work.
Equal Resistors: Current Splits Equally
When all branches have the same resistance, current divides equally: I_n = I_total / n. Three 100Ω resistors with 12A total → each carries 4A. The equivalent parallel resistance is R/n = 100/3 = 33.33Ω.
Current Divider vs. Voltage Divider
| Property | Current Divider (Parallel) | Voltage Divider (Series) |
|---|---|---|
| Circuit topology | Parallel branches | Series resistors |
| What gets divided | Current | Voltage |
| Proportionality | Inversely proportional to R | Directly proportional to R |
| More R means | Less current through that branch | More voltage across that resistor |
| Common quantity | Same voltage across all branches | Same current through all resistors |
| Kirchhoff's Law | KCL (currents sum to I_total) | KVL (voltages sum to V_source) |
Practical Applications: When Current Dividers Matter
- Parallel LED strings: Current imbalance between parallel LED strings (due to LED forward voltage variation) causes uneven brightness and premature failure. Use matched LEDs or individual current-limiting resistors per string.
- Parallel transformer windings: Unequal impedance between parallel transformer secondaries causes circulating currents that waste energy and overheat windings.
- Parallel cable runs: When two conductors are paralleled per NEC 310.10(G), unequal length or impedance causes unequal current sharing — potentially overloading one conductor.
- Current shunt resistors: Precision current measurement uses a known low-resistance shunt to divert a small, measurable current proportional to the main current.
Common Applications
- Parallel LED circuit design — calculate current sharing between parallel LED strings
- Current shunt design — size shunt resistors for ammeter circuits and current sensing
- Parallel conductor current sharing — verify balanced current in paralleled cable runs per NEC 310.10(G)
- Power supply load sharing — analyze current distribution between parallel power sources
- Electronic circuit analysis — solve parallel resistor networks for homework and design
- Fault current distribution — estimate how fault current splits between parallel paths in power systems
- Sensor circuit design — calculate current through sensing elements in parallel measurement circuits
- Battery bank design — analyze current distribution between parallel battery strings
Frequently Asked Questions
What is the current divider rule and when do you use it?
How is the current divider different from a voltage divider?
Why does the lower resistance branch carry more current?
How do I verify my current divider calculation?
What happens to current distribution when parallel branches have very different resistances?
Last updated: April 20, 2026
NEC 2023 · IEEE Standards