Calculations Review Drill

Calculations Review Drill

Instructions The following drill is based on three minutes per question. Be sure to place the slide in presentation mode. The questions will transition automatically The answers will appear for a short period At the end of the slide show, click on the screen and all the questions will be presented without the timer for review.

FivE Steps For Solving Word Problems
Identify the Problem. Begin by determining exactly what the question is asking. Gather Information. Most word problems contain more information than you need to solve the problem. Based on what the question is asking, determine what information you need. Write down the information you need and ignore the unnecessary information Solve the Problem. ... Verify the Answer.

How Calculation problems are developed
Test writers are required to write numerous calculations. They will use the information about a Single Family Dwelling or a Motor to develop multiple questions. Therefore many times, the actual question will contain information that is not needed to answer the question. The following slides contain some examples of how this is done. These slides are not timed and are for reference only.

Motor Calculation Example of multiple questions from the same information.
A 20 HP, three-phase, 480 volt, squirrel cage motor has a full load current nameplate rating of A, a marked service factor of 1.15, it is a Design Letter B motor and the terminations are rated for 75 degrees C. The motor is protected by an instantaneous trip circuit breaker. Here are some of the questions that could be asked. What is the minimum sized overload required for this motor? What is the maximum sized branch circuit, short circuit protection required for this motor? What is the minimum sized THHN conductor which can be used to feed this motor?

Determine the Information you need.
Motor Information Information Needed A continuous duty 20 HP, three- phase, 480 volt, squirrel cage motor has a full load current nameplate rating of A, a marked service factor of 1.15, it is a Design Letter B motor and the terminations are rated for 75 degrees C. The motor is protected by an instantaneous trip circuit breaker. Min. Overload: Need Nameplate FLC and Marked Service Factor: Branch Circuit Short Circuit Protection: Need Table FLC and Type of Protection: Conductor sizing: Need Table FLC : Conductors multiple motors:

LOAD Calculation Example of multiple questions from the same information.
Here are some the questions that could be asked: What is the minimum number of 15A circuits required for the lighting and receptacle circuits? What is the demand of the cooking equipment on the service? What is the demand of the electric clothes dryers on the service? What is the demand of the fastened in place appliances on the service? What is the demand of the heating and air conditioning on the main service? What is the demand of the lighting and the receptacle loads on the service? What is the minimum sized service required for this dwelling? What is the minimum sized service entrance conductor required for this dwelling unit? What is the minimum sized grounding electrode conductor required for this service? A single-family dwelling has 2,654 square feet of habitable space. It is equipped with a 14- kW 240 V, a 3.9 kW electric clothes 240 V, a 3.6 kW water heater at 240 V, a 1.2 kW 120 V, a ¾ HP garbage disposal at 120V, an air conditioner rated at V, and 6.3 kW of electric heat.

Determine the Information you need.
One set of Information How it affects you From one set of information, a test writer can add one sentence to the end and by changing that one sentence, they can write 10 questions which can be added to the randomly drawn database of questions. All of the questions in the database are randomized for your test. You will get a mixture. You may get the same information for three different questions, but each question is different. All you need to do is follow the steps and answer the question.

FivE Steps For Solving Word Problems
Identify the Problem. Begin by determining exactly what the question is asking. Gather Information. Most word problems contain more information than you need to solve the problem. Based on what the question is asking, determine what information you need. Write down the information you need and ignore the unnecessary information Solve the Problem. ... Verify the Answer.

CLiCK ON THIS SLIDE TO START THE TIMED DRILL

Conductors and Cables What is the ampacity of a 10 AWG copper THHN conductor if it is installed in an ambient temperature of 96 degrees F?

ANSWER 36.4 A

LOAD CAlcs What is the demand of a gas range on the main service of a 1500 Square Foot home that is also equipped with gas heat?

Answer 0 VoltAmps Gas range, no electrical demand calculated for service entrance.

A 5 HP, single phase, 120V AC motor has a full load current nameplate rating of amperes, a marked service factor of 1. 0, and it is a design C motor. The motor is a continuous duty motor. What is the maximum sized instantaneous trip circuit breaker which can be used for branch circuit short circuit protection? Motor

Next standard size up is 450 A 240.6
Answer 450 A 56 x 8= 448 Next standard size up is 450 A 240.6

A 5 HP, single phase, 120V AC motor has a full load current nameplate rating of 49.6 amperes, a marked service factor of 1. 0, and it is a design C motor. The motor is a continuous duty motor. What is the maximum sized duel element fuse which can be used for branch circuit short circuit protection? Motor

240.6 Next standard size up is 100 A
Answer 100A 56 x 1.75= 98 Next standard size up is 100 A

Motor A 5 HP, single phase, 120V AC motor has a full load current nameplate rating of 49.6 amperes, a marked service factor of 1. 0, and it is a design C motor. The motor is a continuous duty motor. What is the minimum sized THHN copper conductor which can be used to feed this motor?

Answer 4 AWG Copper 430.22 56 x 1.25= 70 amperes
Use the 75 degree C column of Table (B)(16) because there is not temperature rating listed for the motor. The wire is 90 degrees C and (C) instructs us to use the defaults if we don’t know the temperature ratings. The default for this motor would be 75 C because it is 100 A or less and it is Design C. Answer

A 5 HP, single phase, 120V AC motor has a full load current nameplate rating of amperes, a marked service factor of 1. 0, and it is a design C motor. The motor is a continuous duty motor. What is the minimum sized TW copper conductor which can be used to feed this motor? Assume the motor terminations are rated for 75 degrees C. Motor

Use the 60 degree C column of Table (B)(16) because the motor has a temperature rating of 75 degrees Celsius and the wire has a rating of 60 degrees C (C) instructs us to use the lowest temperature rating in the circuit and that would be 60 degrees C.

What is the current on the primary side of a 480V to 208V three phase, delta Wye transformer if the secondary line current is 116 amperes? The transformers has a turns ratio of 4:1. TransformeR

50.23 Amperes Wye system: Line current is equal to phase current. Secondary phase current is 116 A. From secondary to primary the current will decrease 4 times. 116/ 4= 29 a Delta System: Line current is times greater than phase current. = Answer

A short time duty, three- phase, 208V, 30 HP, wound rotor, design A motor, has a nameplate full load current of amperes, and a marked service factor of What is the minimum sized RHW aluminum conductor which can be used to feed this motor if it is rated for 15 minute use? Motor

ANSWER 2/0 430.22(E) 83.9 x 1.20= 100.68 (Table 430.22(E)
Table (B)(16) Use column for 60 degrees C. The wire is 75 degrees C but we don’t know the temperature rating (C) instructs us to use the defaults. 100 A or less. This is 83.9 amperes, We use 60 C.

A short time duty, three- phase, 208V, 30 HP, wound rotor, design A motor, has a nameplate full load current of amperes, and a marked service factor of What is the minimum sized THHN copper conductor which can be used to feed this motor if it is rated for 5- minute use? Assume all terminations are rated for 90 degrees C. Motor

ANSWER 4 AWG 430.22(E) 83.9 x 1.10= 92.29 (Table 430.22(E)
Table (B)(16) Use column for 90 degrees C. The wire is 90 degrees C and all terms are 90 degrees C.

What is the min. sized common grounding electrode conductor that can be used for five separately derived systems if each system is rated at 50 KVA and is fed with a 4/0 THHN conductor? Grounding

Answer 3/0 Copper or 250 kCMIL aluminum
This appears to be a calculation, however, it is just a code look up. The only information you need is that it is a common grounding electrode conductor for multiple separately derived systems. 250.30(A)(6)(a)(1) states that it must be at least 3/0 Copper or 250 kCMIL aluminum

Conductors If the temperature limitations of equipment termination is not known and the equipment is rated at 100 amperes, then the ampacity of THHN wire connected to a 75-degree C circuit breaker must have the ampacity based upon the ________ degree C ampacity of the conductor sized used.

Not a calculation. A code look up
60C (C)(1)(a)(2) Not a calculation. A code look up 60C 110.14(C)(1)(a)(2) Circuit breaker 75 C Wire 90 C Equipment rated 100 A and not know Use the lowest in the circuit and default for the equipment.

What is the maximum sized duel element, time delay fuse that can be used as branch-circuit, short- circuit protection for a 20 HP, 208V, wound rotor, three-phase motor with a nameplate rating of amperes and a marked service factor of 1.15? The motor is a design B motor.

Answer 110 A

RACEWAY FILL What is the minimum sized EMT raceway that can be used for the following conductors: (10) 1 AWG THHN, (5) 6 AWG THWN-2, (4) 3 RHH with outer covering? Determine the size in metric designators.

ANSWER 63 metric designator
Use Table 5 (Metric Area) to determine volume that the wires take up THHN 1= x 10= 1008 THWN-2 6= x 5= RHH (Without the *) 3= x 4= = USE Table 4, EMT, Over 2 Wires 40%. The smallest conduit size is 63 to fit in volume.

WELDERS What is the maximum sized overcurrent protection allowed for the 3/0 AWG THHN feeder conductors that supply five arc welders. Each welder is rated at 30 amperes at 50 duty cycle? The welders have a 90 degree temperature rating at the terminations.

ANSWER 450 A 630.12(B) T310.15(B)(16) The ampacity of 3/0 THHN in the 90 degree C column is 225 223 x 2= 450 450 is a standard size fuse or circuit breaker in 204.6

LOAD CAlculation What is the demand on the main service entrance of an apartment building for a kW range, a 15.6 kW range, a kW range, a 12.6 kW range and a 9.8 kW range?

ANSWER 22000 Watts T220.55 Note 2 and Note 1

LOAD CALCULATION What is the demand on the main service entrance of a public school for the ten, 11.2 kW , 240V, single phase ranges that are installed in the home economics department and are used for educational purposes?

ANSWER 25,000 Watts T220.55 NOTE 5

LOAD CAlculation What is the demand on the main service of an apartment building for the fifteen, 240V, 4.2 kW dryers located in the laundry room? The service is single phase, 240 V.

ANSWER 32250 Watts 220.54 T220.54 Each dryer has to be calculated at 5000 15 x 5000= 75000 T % - 1% for each dryer exceeding 11. We have 4 more than = 43 75000 x .43= 32250

GENERAL KNOWLEDGE An ammeter installed in a 12-volt DC circuit will read ____________ amperes if the circuit has three resistors wired in series rated at 10 ohms, 12 ohms and 15 ohms.

Answer .32 Amperes Total resistance= 10 + 12 +15= 37 ohms
Current = Voltage/ Resistance E/R= 1 12/ 37= .324

To Continue Click on the Slide