Series Circuit Diagram: Current, Voltage, Resistance Rules and Practical Examples
This is a free printable series diagram: download the diagram as SVG or open it and print to paper or PDF.
A series circuit diagram shows components connected end-to-end in a single, unbroken current path so that the same current flows through every element, while the supply voltage divides across the components in proportion to their resistance.
A series circuit is the simplest of the two fundamental circuit configurations — the other being a parallel circuit. In a series circuit, components are connected sequentially along a single current path with no branches. There is only one route for current to flow from the positive terminal of the supply, through each component in turn, and back to the negative terminal.
The three governing rules of a series circuit (derived from Ohm's Law and Kirchhoff's Voltage Law) are:
1. Current is the same everywhere in the circuit. Because there is only one path, the same number of electrons must pass every point in the circuit per second. If you measure current at any point in a series circuit, you will get the same reading: I_total = I_1 = I_2 = I_3 = … = I_n
2. The total resistance is the sum of all individual resistances. Each component opposes the flow of current and these oppositions add together: R_total = R_1 + R_2 + R_3 + … + R_n. Adding any resistance to a series circuit increases the total resistance and reduces the current.
3. The supply voltage divides across the components in proportion to their resistance. The voltage drop across each component is given by Ohm's Law (V = I × R), and the sum of all voltage drops equals the supply voltage: V_supply = V_1 + V_2 + V_3 + … + V_n. This is Kirchhoff's Voltage Law (KVL). A component with a large resistance takes a proportionally large share of the supply voltage.
Common applications of series circuit principles include: - Resistive voltage dividers (used to create reference voltages in electronics) - Series fuse or circuit breaker protection (one fuse in series with a load; if the fuse blows the circuit opens and the load is protected) - Old-style series-wired Christmas light strings (if one bulb fails open, the entire string goes out — a classic demonstration of series circuit behaviour) - Battery cells in series (multiple cells connected positive-to-negative increase total voltage while the current capacity remains that of a single cell) - Current-sensing resistors (shunt resistors placed in series with a load so the voltage drop across them is proportional to current)
A series circuit diagram is drawn by placing component symbols end-to-end along a continuous line from one supply terminal to the other. Standard IEC 60617 symbols are used for each component. Wire junctions are shown as dots; wire crossings without connection have no dot. Polarity conventions are observed for active components such as diodes, LEDs, and electrolytic capacitors.
The concept of series connection extends beyond resistors to capacitors and inductors. In series: capacitance decreases (1/C_total = 1/C_1 + 1/C_2 + …); inductance adds (L_total = L_1 + L_2 + …).
How to wire series diagram
- Identify the components and their values List every component in the circuit and record its value: resistors (in ohms), the supply voltage (in volts), and any other components such as bulbs (their resistance at operating temperature), diodes, or switches. Collect all nameplate values before beginning any calculations.
- Draw the schematic starting from the supply positive terminal Using standard IEC 60617 symbols (or ANSI/IEEE 315 if working to North American conventions), begin at the supply positive terminal. Draw a horizontal line to the right, then place each component symbol in sequence along the line, connected end-to-end. Complete the circuit by routing back to the supply negative terminal. Label each component with its reference designator and value.
- Calculate the total resistance Sum all resistance values in the circuit: R_total = R_1 + R_2 + R_3 + … + R_n. For components that are not simple resistors (diodes have a forward voltage drop, bulbs have temperature-dependent resistance), use the specified operating values from the component datasheet.
- Calculate the circuit current using Ohm's Law Apply Ohm's Law: I = V_supply / R_total. This single current value applies to every component in the series circuit — there is no need to calculate current separately for each component.
- Calculate the voltage drop across each component For each resistor or load: V_n = I × R_n. Verify your answer by summing all voltage drops — the total must equal the supply voltage (Kirchhoff's Voltage Law): V_1 + V_2 + V_3 + … = V_supply. If the sum does not equal the supply voltage, there is an arithmetic error or a missing component in the analysis.
- Calculate power dissipated by each component Power dissipated by each component: P_n = V_n × I = I² × R_n = V_n² / R_n. Total power from the supply: P_total = V_supply × I. Verify: P_total should equal the sum of all individual component power dissipations. This step is important for determining whether components are within their rated power dissipation limits.
- Annotate the completed diagram with calculated values Mark the calculated current value on the circuit conductor (it is the same everywhere). Mark each component's voltage drop adjacent to the component symbol. Mark each component's power dissipation. A fully annotated series circuit diagram with both specified and calculated values is a complete working document for analysis, verification, and component selection.
Specifications
| Current rule | I_total = I_1 = I_2 = … = I_n (same current at all points) |
|---|---|
| Total resistance | R_total = R_1 + R_2 + … + R_n (resistances add) |
| Voltage rule (Kirchhoff's Voltage Law) | V_supply = V_1 + V_2 + … + V_n (voltage drops sum to supply voltage) |
| Voltage divider ratio | V_n / V_supply = R_n / R_total |
| Total capacitance (capacitors in series) | 1 / C_total = 1/C_1 + 1/C_2 + … + 1/C_n (total capacitance is less than the smallest individual capacitor) |
| Total inductance (inductors in series, no mutual coupling) | L_total = L_1 + L_2 + … + L_n (inductances add, same as resistors) |
| Power dissipated by each component | P_n = I² × R_n = V_n × I = V_n² / R_n |
| Total power from supply | P_total = V_supply × I = I² × R_total; equals the sum of all individual component power dissipations |
Safety warnings
- When series circuit experiments or demonstrations involve mains-voltage (230V/120V AC) components, all work must be carried out by a licensed electrician in accordance with applicable wiring standards (NEC/NFPA 70, BS 7671, AS/NZS 3000, IEC 60364). Low-voltage DC circuits (below 50V DC) used for educational purposes are generally safe but should still be treated with care — large capacitors and batteries can deliver high short-circuit currents.
- Always isolate and verify dead before modifying any series circuit in a fixed electrical installation. Even though a series circuit with an open switch appears safe, the conductor on the supply side of the switch remains live.
- Include overcurrent protection (a fuse or circuit breaker in series) in any practical series circuit. Without a fuse, a short circuit across any component will allow unrestricted current to flow, potentially causing overheating, insulation damage, and fire.
- In series battery connections, verify the correct polarity of each cell before connecting — a reversed cell reduces total voltage rather than adding to it and can be driven into reverse charge, causing damage or, in the case of lithium cells, a safety hazard.
- Series circuits with capacitors: capacitors charged in a series configuration retain charge after the power source is disconnected. Discharge capacitors safely through a resistor before touching any terminals in a capacitor-containing series circuit.
Tools needed
- Multimeter with DC and AC voltage, resistance, and current functions (to verify circuit values against calculations)
- Breadboard and jumper wires (for constructing and modifying prototype series circuits)
- Resistor colour code chart or digital component identifier (for identifying resistor values)
- Variable bench power supply with current limiting (for safe series circuit experiments)
- Graph paper or electrical CAD software (for drawing the series circuit schematic)
- Scientific calculator (for Ohm's Law, power, and voltage divider calculations)
Common mistakes
- Forgetting that adding any resistance to a series circuit reduces the current through all other components — a common error when adding LED indicator lamps or measurement shunts to an existing series circuit.
- Connecting an ammeter in parallel across a component instead of in series in the circuit — an ammeter has very low internal resistance and will create a near-short circuit across the component, potentially blowing the ammeter fuse and damaging the circuit.
- Connecting a voltmeter in series instead of in parallel across the component being measured — a voltmeter has very high internal resistance and will effectively open-circuit the series path, blocking nearly all current.
- Confusing series and parallel resistor formulas — resistors in series add directly (R_total = R_1 + R_2 …); resistors in parallel use the reciprocal sum formula (1/R_total = 1/R_1 + 1/R_2 …). Applying the parallel formula to a series circuit will give a dramatically incorrect total resistance.
- Selecting component power ratings based only on the nominal current — use the calculated power dissipation (P = I² × R) and select components rated for at least twice the calculated value to allow a reasonable derating margin.
Troubleshooting
- No current flowing in the series circuit — all components are off
- Cause: Open circuit at some point in the series path: blown fuse, open switch left in open position, broken wire, or failed component (open-circuit resistor, open-circuit LED) Fix: With power off, use a multimeter in continuity mode to test each segment of the circuit from one supply terminal to the other. The continuity will be present up to the open-circuit point and absent beyond it. Identify the open-circuit component or break and repair or replace it.
- Current flows but is significantly lower than calculated
- Cause: One or more components have a higher resistance than assumed — resistors outside tolerance, a lamp cooler than expected, a bad connection introducing additional resistance, or a component partially failed to high resistance Fix: With power off, measure the resistance of each component individually. Compare to the design value. Identify any component with resistance significantly above its rated value or any connection with measurable resistance (a good connection should read zero ohms in continuity mode).
- Voltage across one component is much higher than calculated
- Cause: A component elsewhere in the series circuit has failed to high resistance or open circuit — all the supply voltage drops across the remaining path, and the remaining components share a higher proportion of the supply voltage Fix: Measure voltage across each component in turn. The voltages must sum to the supply voltage. The component with an unexpectedly high voltage drop is absorbing the voltage that should be shared with the failed component — measure resistance of all components when powered off to find the high-resistance or open-circuit fault.
Frequently asked questions
What is the main characteristic that defines a series circuit?
In a series circuit, all components are connected in a single, unbranched current path. The same current flows through every component. If the circuit is broken at any point — a blown fuse, an open switch, or a failed component — the entire circuit loses current and all components stop operating simultaneously.
How do you calculate total resistance in a series circuit?
Add the individual resistance values together: R_total = R_1 + R_2 + R_3 + … + R_n. For example, three resistors of 10 Ω, 22 Ω, and 47 Ω in series give R_total = 79 Ω. The current is then I = V_supply / R_total by Ohm's Law.
Why does adding more components to a series circuit reduce the current?
Every component in a series circuit adds to the total resistance. By Ohm's Law, current I = V / R. With a fixed supply voltage V, increasing R_total decreases I proportionally. This is why a series fuse protects a circuit — when it blows (open-circuits), R_total becomes effectively infinite and current drops to zero.
How does voltage divide in a series circuit and how do I calculate the voltage across each component?
Each component's voltage drop is V_n = I × R_n, where I is the common series current. The ratio of each voltage drop to the supply voltage equals the ratio of that component's resistance to the total resistance: V_n / V_supply = R_n / R_total. This principle is used deliberately in a resistive voltage divider to produce a reference voltage.
What happens when one component in a series circuit fails open-circuit?
An open circuit at any point in a series circuit interrupts the single current path — current drops to zero throughout the entire circuit. All other components lose power simultaneously. This is the primary disadvantage of series wiring for loads that must operate independently; it is also the design principle behind series fuse protection.
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