ANSWERS TO QUESTIONS IN SAFETY IN THE LABORATORY

Answer Key to Accompany Lab Exercises for Electricity for Refrigeration, Heating, and Air Conditioning NOTE: (For Complete File, Download link at the end of this File) 1 / 4

Chapter 1 © 2019 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.1

ANSWERS TO QUESTIONS IN SAFETY IN THE LABORATORY

• Accidents happen when we least expect them. In the HVAC/R industry, workers are

exposed to sharp objects, excessive heat, excessive cold, airborne contaminants, chemicals, electricity and other potential hazards. In addition, workers must lift heavy objects, work on ladders and other elevated platforms and be subjected to a number of other hazards. Personal protection equipment, when properly work, helps to reduce the chance of getting injured on the job.

• It is always important to be aware of your surroundings. In the event that an area has to

be evacuated, knowing how to vacate the space beforehand will help save valuable time when an emergency occurs. Being aware of unsafe surroundings can help you avoid them. Also, being aware of what others are doing can help you remain safe on the job by protecting yourself from potential hazards that are posed by others.

• Being impaired reduces your response time to hazardous situations and also clouds

your judgment, increasing the possibility of getting injured on the job.

• The purpose of CPR is to maintain oxygen flow to the brain in the event that someone

has stopped breathing. Keeping oxygen flowing to the brain greatly increases an individualʼs chance of surviving an accident and reduces the chance of suffering brain damage. If an individual is breathing, CPR should not be performed. In order to perform CPR, you must be properly trained and certified to do so.

• It is important to wear a back brace and lift with your legs, not your back. If an object is

heavy, a team lift is recommended.

• Pressurized vessels should be transported vertically, with the caps in place. If using a

cart to transport tanks, make certain that the tanks are secured to the cart to prevent rolling off. Never roll tanks across the floor to move them from one place to another.

• Possibility of receiving an electric shock, and possibly damaging system components,

especially electronic control devices.

• Wait for rotating machinery to come to a complete stop before touching. Never try to

stop rotating machinery with your hands. Avoid wearing loose fitting clothing that can get caught in the machinery. Keep fingers away from any rotating machinery. 2 / 4

Chapter 2 © 2019 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.2

ANSWERS TO QUESTIONS IN MEASURING ELECTRICAL CHARACTERISTICS

AND PERFORMING ELECTRICAL CALCULATIONS

• The current will increase.
• The current will decrease.
• A resistive load.

4. E = I × R, R = E ÷ I, I = E ÷ R.

• Ohmʼs law holds true when the power factor is equal to 1, meaning that the voltage and

current are in phase with each other. This means that the voltage peaks at the same time the current peaks. If the voltage and current are out of phase with each other, there will be errors in the Ohmʼs law calculations. 3 / 4

Chapter 3 © 2019 Cengage Learning. All Rights Reserved. May not be scanned, copied, or duplicated, or posted to a publicly accessible website, in whole or in part.3

COMPLETED CHART FROM ELECTRICAL LOAD IDENTIFICATION

DEVICE

SWITCH RESISTIVE

LOAD

INDUCTIVE

LOAD

POWER FACTOR

N/A LOW

HIGH (Close to 1) High Limit Control X X Solenoid Coil X X High Pressure Control X X Motor Winding X X Bi-Metal Overload X X Electric Heating Element X X Line-Voltage Thermostat X X Relay Coil X X N.C. Set of Contacts X X Circuit Breaker X X Low-Voltage Thermostat X X Electric Toaster Heating Elements X X Low Pressure Control X X Contactor Coil X X Incandescent Light Bulb X X Electromagnet X X N.O. Set of Contacts X X Transistor X X Aquastat X X Transformer Winding X X

ANSWERS TO QUESTIONS IN ELECTRICAL LOAD IDENTIFICATION

• Resistive loads generate primarily light and or heat (plus a small magnetic field).
• Inductive loads primarily generate a small magnetic field (plus some heat).
• Power factor is the ratio of realized power to calculated power and ranges from 0 to 1.
• The strength of the magnetic field generated around the conductor is proportional to the

current. If the wire is formed into a coil, the current sensed is equal to the current flow times the number of turns in the coil, thereby increasing the strength of the magnetic field.

• The voltage and current are in phase with each other.
• Add a run capacitor to the circuit.

ANSWERS TO QUESTIONS IN SERIES CIRCUITS

• The resistance of the 75-W bulb will be lower than the resistance of the 100-W bulb. Since

power is a function of voltage and current, and the voltage supplied to both bulbs will be the same, the current must be higher through the higher-wattage bulb. From Ohmʼs law we know that lower resistances will allow more current to flow. Therefore, as the wattage of a light bulb increases, the resistance of the bulb will drop.

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