Let’s test your electrician skills
These are not-so-easy, but also not-too-hard questions for you to try to answer and test your electrician skills. Whether you are a novice in a field of electrical engineering or a professional electrician, these questions will move your brain cells for sure! To check your results, take a peek for answers at the bottom of article.
Building “A” is supplied with 120/240 volt single-phase power from building “B” on the same property. “B” is supplied from a three-wire with two ungrounded conductors and one neutral without any metallic water pipe or other metal equipment connections to the building or equipment ground fault protection installed.
The neutral conductor must:
B. Not be connected to a grounding electrode in either building
C. Be bonded to the disconnect enclosure in the second building and connected to a grounding electrode
D. Tie into the ungrounded conductor of one of the buildings with a grounding jumper
A feeder runs from one part of a building to another under the floor in two parallel sets of rigid non-metallic conduits with type RHW copper conductors size AWG #500 and is protected by 800 ampere fuses. It must have a minimum size copper equipment grounding conductor in each conduit run of no less than which of the following:
B. 20 AWG
C. 10 amps
D. 5 AWG
A surge arrestor for a 480 volt electrical system requires a connecting conductor that is #14 copper or larger.
If a single family dwelling unit has 2680 square feet of living space and all of the 120 volt general illumination circuits are rated at 15 amperes, then the minimum number of circuits required is which of the following:
A single family dwelling with 2400 square feet of living area has a 120/240 volt three-wire electrical service and contains the following:
- 3.5 kW 240 volt electric water heater,
- 12 kW electric range,
- 1.5 horsepower 240 volt central air conditioner,
- 1/2 horsepower 120 volt garbage disposal,
- 1/3 horsepower 120 volt furnace blower motor, a 1.2 kW 120 volt dishwasher, and
- 5 kW clothes dryer.
The total minimum load required for the general illumination, small appliances, and laundry without any demand factors would be which of the following:
B. 7200 VA
C. 11700 VA
D. 15000 VA
If a three-phase 75 kVA transformer is connected to the primary at 480 volts and 120/208 volts on the secondary, then the full load current of the transformer secondary would be which of the following:
B. 208 amps
C. 90 VA
D. 25 VA
In order to correct the power factor, a three-phase, 480 volt, 92 kVAR capacitor bank located 6 feet from the main service of a 3200 square foot office building has a minimum required ampere rating for the conductors in the capacitor bank of which of the following:
B. 180 amps
C. 150 amps
D. 110 amps
In an 8 unit apartment building, each kitchen contains a 3.5 kW 240 volt electric range. The demand load for the electric service to the building must include an allowance for the minimum demand load of all of the ranges, which would be which of the following:
B. 21 kVA
C. 14 kVA
D. 7.5 kVA
A retail store has 3000 square feet and 30 feet of show window. The service is a 120/240 volt single phase 3-wire service, and there is an actual connected lighting load of 8500 VA.
There are a total of 80 duplex receptacles. Given these facts, the total calculated load is which of the following:
B. 12200 VA
C. 16200 VA
D. 28400 VA
A project requires the installation of twelve 1.4 ampere, 120 volt, fluorescent lights fixtures on two 20 amp branch circuits, as well as three 120 volt, 5.6 ampere electric fans on individual circuits in a building with a 120/240 single phase three-wire electric service.
The minimum neutral current allowed for these loads is which of the following:
B. 5.6 amps
C. 16.8 amps
D. 33.6 amps
To prove your electrician skills, your results should be the same as provided answers. NEC articles mentioned in answers you can observe in a free draft version of NEC 2014 //
- C – Reference Section [250.32(B)(1)]
- A – Reference Table [250.122]
- A – Reference Section [280.21]
- A – Reference Sections [210.11(A)] and [220.423(A)] for minimum load requirements. Divide the load by 120 volts, then divide this value into the circuits to determine the number of circuits required.
3 VA ÷ 2680 feet 2 = 8040 VA;
120 volts × 15 amps (per circuit) = 1800;
8040 ÷ 1800 4.5 (rounded up to 5)
- C – Reference Table [220.3(A)] to see that 3 VA is required for every square feet of living area.
2400 square feet × 3 VA = 7200 VA.
The small appliance load in Section [220.11(C)(2)] is 1500 VA and comes to 2 small appliance loads.
1500 VA × 3 = 3000;
Section [210.11(C)(2)] requires 1500 VA for a dwelling laundry circuit.
7200 + 3000 + 1500 = 11700 VA.
- B – Use formula Csecondary = 75kVA × 1000 / 1.73 × 208v = 208 amps
- C – The first step is to calculate how much current will be going to the capacitor bank once it is energized, which is the same formula you would use to calculate the full load current of a transformer, except you need to use kVAR’s instead of kVA.
Ccapacitor = 92kVAR × 1000 / 1.73(3 phase) × 480v = 110.8 amps
Next you need to find the minimum ampere rating of the conductors in the capacitor bank using the requirement in Section [460.8(A)], and you will find that the ampacity cannot be more than 135% (which is 1.35).
Multiply the capacitor current of 110.8 × 1.35 = 149.58 rounded up to 150 amps.
- B – Reference [Section 220.17] lists a demand factor of 0.75 for four or more appliances.
8 ranges × 3.5 kW each = 28 × 0.75 demand factor = 21 kVA
- D – Reference Chapter 9, Annex D, Example D3
- A – Balance the load by placing 4 fixtures and 2 fans on one circuit and 8 fixtures and one fan on the other as shown below:
LEG 1 LEG 2 4 Fixtures 5.8 amps 8 fixtures 11.2 amps Fan 5.6 amps Fan 5.8 amps Fan 5.6 amps Total // 16.8 amps 16.8 amps
Reference // Electrician’s Exam Study Guide (Purchase at Amazon)