Electrical Safety and Shock Factors

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Questions and Answers

What does an ohmmeter indicate when it registers unlimited resistance?

It indicates an open circuit, represented by the symbol for infinity (∞) or the letters OL for overloaded.

What are the three factors that determine whether an electrical shock is fatal?

The three factors are how much current passes through the body, how long the current passes through, and whether the current passes through the heart.

How does an analog ohmmeter visually indicate unlimited resistance?

The needle of the analog meter goes all the way over to the peg, also known as being pegged out.

At what current level does a person typically start to feel a painful shock?

A painful shock typically starts between 8 mA to 15 mA. Signup and view all the answers

What analogy is used to explain the concept of an open circuit?

A drawbridge is used as an analogy, where the opened bridge represents infinite resistance, stopping the traffic (electron flow). Signup and view all the answers

What factors contribute to voltage drop in an electrical conductor?

Voltage drop can be caused by an electrical load, a loose connection, or an undersized conductor. Signup and view all the answers

What happens to the heart at a current level of 100 mA to 200 mA?

Current levels of 100 mA to 200 mA can cause painful shock and induce ventricular fibrillation, a fatal heart condition. Signup and view all the answers

Why is it important to select the appropriate size of wire for electrical conductors?

Selecting the right wire size minimizes voltage drop, preventing the conductor from overheating and ensuring the load receives its designed voltage. Signup and view all the answers

Describe what an ohmmeter is used for.

An ohmmeter is an instrument used to check resistance, continuity, and to ensure that electrical circuits are complete. Signup and view all the answers

What does a continuity check indicate in electrical circuits?

A continuity check indicates a complete path for electron movement, confirming that the circuit is not broken. Signup and view all the answers

Explain why you shouldn't use the meter multipliers (R × 10, R × 100) when checking continuity.

You shouldn't use meter multipliers to avoid inaccuracies in low resistance measurement which are crucial for continuity checks. Signup and view all the answers

What current level can cause severe burns and possibly stop the heart?

Current levels over 200 mA can cause severe burns and muscular contractions that may stop the heart. Signup and view all the answers

Can electrical current flow in an open circuit and why?

No, electrical current cannot flow in an open circuit because there is a break in the path for electron movement. Signup and view all the answers

Study Notes

Electrical Shock Factors

Three primary factors influence the fatality of an electrical shock: current (amperage), duration of exposure, and the current's path through the body, particularly through the heart.
A milliampere (mA) equals 1/1000 of an ampere; currents between 100 mA to 200 mA can be lethal.

Safe and Unsafe Current Values

Safe Current Values:
- 1 mA: No sensation or feeling.
- 1 mA to 8 mA: Shock sensation, non-painful, and no muscle control loss.
Unsafe Current Values:
- 8 mA to 15 mA: Painful shock, no muscle control loss.
- 15 mA to 20 mA: Painful shock with hand muscle contraction, inability to release grip.
- 20 mA to 75 mA: Painful shock, severe muscle contractions, significantly difficult breathing.
- 100 mA to 200 mA: Painful shock causing ventricular fibrillation, potentially fatal, requires immediate medical intervention.
- Over 200 mA: Causes severe burns and significant muscle contractions, collapsing the heart; prompt artificial respiration can revive victims.

Ohmmeter and Continuity Testing

An ohmmeter measures electrical resistance, available in analog or digital formats.
It is used to check continuity, ensuring a complete circuit for electron flow; low resistance indicates intact circuits.
When measuring continuity, the ohmmeter should be set on the lowest resistance scale (R x 1) for accurate readings.
Unlimited resistance indicates an open circuit, shown by the symbol for infinity (∞) on analog meters or OL (overload) on digital meters.

Circuit Continuity and Resistance

An open circuit may result from issues like open switches, blown fuses, or broken wires, preventing electron flow.
A drawbridge analogy illustrates open circuits: when the bridge is raised, traffic (electron flow) stops until it closes.

Voltage Drop

Voltage drop refers to the reduction in voltage across a circuit, caused by loads, loose connections, or undersized conductors.
All conductors exhibit some resistance, which leads to voltage drop, affecting the load’s performance.
Proper wire selection is crucial to minimize voltage drop; excessively small wires can lead to overheating and insufficient voltage for the load.
Loads operate correctly within ±5% of their rated voltage; voltage drop should ideally occur across the load's resistance.
An accurate multimeter can detect excess voltage drop during operation.

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Description

This quiz explores the critical factors affecting the fatality of electrical shocks, including current, duration, and path through the body. It also covers safe and unsafe current values to help understand the risks associated with electrical exposure. Test your knowledge on what constitutes a safe versus hazardous electrical environment.