NFPA ELECTRIC VEHICLE SAFETY FOR EMERGENCY RESPONDERS Module II : Basic Electrical Concepts And...

NFPA ELECTRIC VEHICLE SAFETY FOR EMERGENCY RESPONDERS

Module II:Basic Electrical

ConceptsAnd Hazards

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NFPA ELECTRIC VEHICLE SAFETY FOR EMERGENCY RESPONDERSModule II: Basic Electrical Concepts and Hazards

Describe basic electrical concepts that pertain to P/HEVs and EVs.

Terminal Objective

● Define basic electrical terms.

● Understand the difference between electrical systems found in structures and those found in P/HEVs and EVs.

● Understand how electricity affects the body and how to protect against electric shock.

Enabling Objectives

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Module II Objectives


● Electrical terms

● Types of electricity

● Understanding electrical circuits

● Building electrical systems vs. vehicle electrical systems

● Effects of electricity on the body

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Module II Outline

Voltage: Electrical Potential

• Comparable to water pressure or PSI in a hose.

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Basic Electrical Terms

• Measured in Volts.

Current: Quantity of electrons flowing

• Comparable to the rate of flow of water or gallons per minute (GPM).

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• Measured in Amperes.

Resistance: A material’s opposition to conducting current

• Comparable to friction loss in hose lines or appliances.

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• Measured in Ohms.

DC CircuitsTypically found in electronic devices that utilize battery power and some industrial applications.

AC CircuitsFound anywhere electricity is supplied by the utility company from the power grid, such as in buildings.

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Alternating Current

Current repeatedly reverses direction.

DIRECT CURRENT VS. ALTERNATING CURRENT

Direct Current

Current always flows in the same direction.

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Types of Electricity Found in P/HEVs and EVs

DC ● Found in all P/HEVs and EVs.

● All use batteries for electrical storage.

AC ● Found in some P/HEVs and EVs.

● These models use AC motors.

● DC is converted to AC.

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● With both AC and DC, there must be a completed path, or circuit, for current to flow.

● A switch creates a break in the circuit when “OFF”.

● Turning the switch “ON” completes the circuit, allowing current to flow.

● Injury can occur when a person’s body becomes part of a circuit by completing a path for current.

Understanding Electrical Circuits

OFF

ON


Video

Electrical Circuits

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Video

Electrical Circuits

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● All HV circuits (AC or DC) are isolated from the vehicle chassis.

● Safeties will cause a vehicle HV system to shut down should chassis become part of the circuit.

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HV POWERSOURCE

ELECTRICMOTOR

Vehicle vs. Building Electrical Circuits

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● Unlike in a structure, the earth is not part of the circuit design.

● Introducing a path to ground (touching or spraying water) will not, by itself, complete a circuit.

Vehicle vs. Building Electrical Circuits

ELECTRICMOTOR

● To receive a shock, you must place your body in a position to become part of a circuit.

HV POWERSOURCE

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● Human body and PPE provide some resistance to electricity.

How Electricity Affects the Body

● Voltage must be high enough to overcome resistance before it can enter your body.

● Environmental conditions, like being wet, can greatly reduce resistance.

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How Electricity Affects the Body

● Once resistance is overcome, Amperage usually determines degree of damage.

● Circuits in P/HEVs and EVs have both the voltage and amperage to be considered highly dangerous.

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● 9V battery: Not enough voltage to overcome resistance of dry skin

How Electricity Affects the BodyExamples

● Stun Gun: High voltage, but not enough amps to do real damage.

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How Electricity Affects the BodyAnalogy

● A 2 PSI low pressure hose flowing at 3 GPM would not hurt if aimed at you.

● A 1000 PSI pressure washer, pushing the same 3 GPM could seriously harm you.

● The high pressure (voltage) allows the current to overcome your skin’s resistance.

OBSERVABLE EFFECT

2407040

Startle ReactionCan’t let go

Electrical BurnsPossible Ventricular Fibrillation

Milliamps (1000 mA = 1 A)

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DC Current Effect on Humans

Some models of P/HEV and EV generate current in excess of 100 Amps, or 100,000 mA

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Effect thresholds based on full grown adult physiology. Effects on smaller persons or children may

occur at lower amperage.

Personnel Protection Devices for Specific Applications, Electric Power Research Institute, Project 6850-

02, Final Report, October 1999, prepared by Underwriters Laboratories Inc.

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AC Current Effect on Humans

OBSERVABLE EFFECT

833105702066.5 Startle Reaction

GFCI will tripCan’t let go

Muscle Contraction (Respiratory Paralysis)Electrical Burns

Ventricular Fibrillation

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Current Used by a 100 Watt Light Bulb

Milliamps (1000 mA = 1 A)

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Effect thresholds based on full grown adult physiology. Effects on smaller persons or children may

occur at lower amperage.

Personnel Protection Devices for Specific Applications, Electric Power Research Institute, Project 6850-

02, Final Report, October 1999, prepared by Underwriters Laboratories Inc.

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Some models of P/HEV and EV generate current in excess of 100 Amps, or 100,000 mA


?What is the difference between Voltage and

Current?

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Voltage is the electrical potential of a circuit, or the “pressure” of the current.

Current is the rate of flow, measured in amperes or

amps.

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Answer


?What are the two types

of electricity used in P/HEVs and EVs?

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Direct Current (DC)and

Alternating Current (AC)

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Answer


?For current to flow (AC or DC),

what must be completed?

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A Circuit or path

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Answer


?What is a major

difference between a HV electrical system in a car and those found

in structures?

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Vehicle HV Systems are isolated from the chassis,

where structures’ electrical systems are grounded to the

earth.

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Answer


?The risk of a shock

occurs when the body becomes part of

the_________?

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Circuit

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Answer


● Electrical Terms.● Types of Electricity.● Understanding Electrical Circuits.● Building Electrical Systems vs. Vehicle

Electrical Systems.● How Electricity Affects the Body.

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Module Summary

NFPA ELECTRIC VEHICLE SAFETY FOR EMERGENCY RESPONDERS Module II : Basic Electrical Concepts And...

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