⚡ Parallel Circuit, Open Circuit & Short Circuit
Effects, Working, Diagrams, Formulas, Comparison Chart & Electrical Safety
🔵 Parallel Circuit
Multiple current paths are available. The voltage across each branch is the same.
Multiple Paths → Normal Operation
🟢 Open Circuit
The conducting path is broken. Therefore, current cannot flow through the open path.
Broken Path → Current = 0
🔴 Short Circuit
An unintended low-resistance path can cause a very high current.
Low Resistance → High Current
⚡ What is an Electrical Circuit?
An electrical circuit is a complete conducting path through which electric current can flow. A simple circuit normally contains a source, conductor, control device and load.
For example, a battery, switch and lamp connected with wires form a simple circuit. When the switch is closed, current flows through the lamp and it glows.
- V = Voltage in volts (V)
- I = Current in amperes (A)
- R = Resistance in ohms (Ω)
🔵 1. Parallel Circuit
A parallel circuit is a circuit in which two or more electrical loads are connected across the same two supply points. Therefore, the voltage across each branch is the same.
Animated current path: The dashed lines represent current paths through the parallel branches.
Effects of Parallel Circuit
- Voltage across each branch remains the same.
- Total current divides among the branches.
- Total current equals the sum of branch currents.
- One branch can be switched OFF while other branches continue operating.
- Adding another load generally reduces total equivalent resistance.
- Total supply current generally increases when another load is connected.
Domestic electrical loads are commonly connected in parallel so that different appliances can operate independently.
🟢 2. Open Circuit
An open circuit occurs when the conducting path is broken or interrupted. Since there is no complete path, current cannot flow through the open circuit.
Effects of Open Circuit
- Current becomes zero through the open path.
- The load normally does not operate.
- Ideal open-circuit resistance is considered infinite.
- Voltage may still exist across the open point.
- The circuit becomes incomplete.
Common Causes
- Broken wire
- Open switch
- Blown fuse
- Loose terminal
- Damaged conductor
- Broken connection inside equipment
🔴 3. Short Circuit
A short circuit occurs when two points at different electrical potentials become connected through an unintended path having very low resistance.
Effects of Short Circuit
- Very high current may flow through the fault path.
- Conductors may become overheated.
- Fuse may blow.
- MCB/circuit breaker may trip.
- Sparking or arcing may occur.
- Electrical equipment can be damaged.
- A serious fault can create a fire hazard.
Never intentionally create a short circuit on a live electrical supply. Electrical fault investigation and repair should be performed using appropriate isolation, testing procedures, PPE and workplace safety practices.
📊 Comparison Chart
| Feature | 🔵 Parallel | 🟢 Open | 🔴 Short |
|---|---|---|---|
| Current Path | Multiple paths | Broken path | Unintended low-resistance path |
| Resistance | Depends on loads | Very high / ∞ | Very low / nearly 0 |
| Current | Divides among branches | 0 A | Very high |
| Voltage | Same across branches | May appear across open point | Nearly 0 V across ideal short |
| Load | Can operate independently | Normally OFF | May be affected/damaged |
| Example | Domestic wiring | Broken wire | Damaged insulation |
| Protection | Fuse / MCB as required | Usually no excessive current | Fuse / MCB should disconnect fault |
📈 Current Condition Chart
This visual comparison is for understanding the general current condition. It is not a measurement of a particular electrical system.
🧮 Effect on Resistance and Current
The relationship between voltage, current and resistance is explained by Ohm's law:
In an open circuit, resistance is extremely high. Therefore, current is practically zero.
In a short circuit, resistance is extremely low. Therefore, the fault current can become very high, depending on the electrical source and system impedance.
In a parallel circuit, the equivalent resistance is lower than any individual branch resistance for ordinary positive resistances, and the total current is the sum of branch currents.
🏠 Why Parallel Connection is Used in House Wiring
⚡ Same Voltage
Each branch receives the required supply voltage.
🔌 Independent Control
Each appliance can be controlled independently.
💡 Reliable Operation
Switching one branch OFF does not necessarily turn other branches OFF.
🔧 Open Circuit Fault Finding
When electrical equipment does not operate, an open circuit can be one possible reason. A technician may inspect switches, fuses, terminals, wires and connections using appropriate electrical test instruments.
- Check the supply condition.
- Check the switch and fuse.
- Inspect terminals and connections.
- Check for broken conductors.
- Use suitable testing instruments according to safety procedures.
🛠️ Short Circuit Fault Finding
A short circuit is a potentially dangerous electrical fault. Common causes include damaged insulation, incorrect wiring, moisture, loose wire strands and faulty equipment.
- Repeated MCB tripping
- Fuse blowing
- Sparking
- Burning smell
- Overheated conductor
- Unexpected power interruption
📐 Important Electrical Formulas
🎯 Important Points for ITI Electrician Students
🔵 Parallel
- Multiple paths
- Same voltage
- Current divides
🟢 Open
- Broken path
- R = ∞
- I = 0
🔴 Short
- Very low resistance
- Very high current
- Protection may trip
❓ Frequently Asked Questions
1. What happens in a parallel circuit?
Current divides among different branches while the voltage across each branch remains the same.
2. What happens in an open circuit?
The conducting path is broken, so current through the open path is zero.
3. What happens in a short circuit?
A very low-resistance unintended path can cause very high current and may cause a fuse or circuit breaker to operate.
4. What is the resistance of an ideal open circuit?
The resistance of an ideal open circuit is considered infinite.
5. What is the resistance of an ideal short circuit?
The resistance of an ideal short circuit is considered zero.
6. Why are domestic loads connected in parallel?
Parallel connection allows appliances to receive the required voltage and operate independently.
⚡ Quick Revision
🔵 Parallel → Multiple Paths
🔵 Parallel → Same Voltage
🟢 Open → Broken Path
🟢 Open → Current = 0
🔴 Short → Very Low Resistance
🔴 Short → Very High Current
🛡️ Fuse / MCB → Protection
✅ Conclusion
Parallel circuit, open circuit and short circuit are basic but very important topics in electrical engineering and ITI Electrician trade theory.
A parallel circuit provides multiple current paths and has the same voltage across each branch. An open circuit has a broken path, resulting in zero current through that path. A short circuit creates an unintended low-resistance path and can produce dangerously high current.
Understanding these conditions helps electricians and students with circuit analysis, troubleshooting, maintenance and electrical safety.
🔵 Parallel Circuit = Multiple paths + Same voltage across branches
🟢 Open Circuit = Broken path + Very high resistance + Zero current
🔴 Short Circuit = Very low resistance + Very high current
Educational Note: This article is intended for electrical and ITI Electrician trade theory study. Always follow applicable electrical safety standards and workplace procedures when working on electrical installations.