Daily review: How to Wire a 20A/250V, NEMA 2-20…

Q: Which of the following characterizes a NEMA 2-20 receptacle?

It is rated for 20A and 250V and lacks a grounding connection. — NEMA 2-20 is a non-grounding 250V configuration typically used for specialized legacy equipment.

Q: What is the primary risk when wiring a non-grounding NEMA 2-20 receptacle?

The lack of an equipment grounding conductor provides no fault path to ground. — Non-grounding receptacles lack a safety ground, meaning chassis faults cannot be cleared by the OCPD.

Q: In a series AC circuit, what is the correct formula for total impedance (Z)?

Z = sqrt(R² + (Xl - Xc)²) — Total impedance is the vector sum of resistance and net reactance.

Q: According to the Voltage Divider Rule (VDR), the voltage across resistor R1 in a series circuit of R1 and R2 is:

Vout = Vin * (R1 / (R1 + R2)) — VDR states the voltage across a resistor is proportional to its share of the total resistance.

Q: What happens to the total impedance (Z) of a series RLC circuit if the frequency increases well above the resonant frequency?

Z increases because inductive reactance dominates. — Inductive reactance (XL = 2?fL) increases with frequency, increasing total impedance.

Q: When wiring a NEMA 2-20, what is the standard wire color for the two 'hot' conductors?

Two blacks, or one black and one red. — A 250V circuit uses two ungrounded (hot) conductors; colors vary but usually avoid white or green.

Q: If you apply the Voltage Divider Rule to complex impedances (Z1 and Z2), the formula for voltage across Z1 is:

Vz1 = Vin * (Z1 / (Z1 + Z2)) — The VDR holds for complex impedances as it does for pure resistances.

Q: Which factor must be considered when calculating the ampacity for a NEMA 2-20 circuit?

Continuous load requirements and conductor gauge. — Ampacity is determined by wire gauge, insulation type, and whether the load is continuous.

Q: In a circuit with 10 ohms resistance and 10 ohms capacitive reactance in series, what is the phase angle?

-45 degrees — The angle is arctan(-Xc/R) = arctan(-10/10) = -45 degrees.

Q: Why is the NEMA 2-20 considered 'non-grounding'?

Because the NEMA configuration lacks a pin/slot for a safety ground. — The NEMA 2 series specifically refers to a 2-pole, 2-wire configuration with no equipment ground.

Question 1 of 10

Which of the following characterizes a NEMA 2-20 receptacle?

NEMA 2-20 is a non-grounding 250V configuration typically used for specialized legacy equipment.

Question 2 of 10

What is the primary risk when wiring a non-grounding NEMA 2-20 receptacle?

Non-grounding receptacles lack a safety ground, meaning chassis faults cannot be cleared by the OCPD.

Question 3 of 10

In a series AC circuit, what is the correct formula for total impedance (Z)?

Total impedance is the vector sum of resistance and net reactance.

Question 4 of 10

According to the Voltage Divider Rule (VDR), the voltage across resistor R1 in a series circuit of R1 and R2 is:

VDR states the voltage across a resistor is proportional to its share of the total resistance.

Question 5 of 10

What happens to the total impedance (Z) of a series RLC circuit if the frequency increases well above the resonant frequency?

Inductive reactance (XL = 2?fL) increases with frequency, increasing total impedance.

Question 6 of 10

When wiring a NEMA 2-20, what is the standard wire color for the two 'hot' conductors?

A 250V circuit uses two ungrounded (hot) conductors; colors vary but usually avoid white or green.

Question 7 of 10

If you apply the Voltage Divider Rule to complex impedances (Z1 and Z2), the formula for voltage across Z1 is:

The VDR holds for complex impedances as it does for pure resistances.

Question 8 of 10

Which factor must be considered when calculating the ampacity for a NEMA 2-20 circuit?

Ampacity is determined by wire gauge, insulation type, and whether the load is continuous.

Question 9 of 10

In a circuit with 10 ohms resistance and 10 ohms capacitive reactance in series, what is the phase angle?

The angle is arctan(-Xc/R) = arctan(-10/10) = -45 degrees.

Question 10 of 10

Why is the NEMA 2-20 considered 'non-grounding'?

The NEMA 2 series specifically refers to a 2-pole, 2-wire configuration with no equipment ground.

Daily review: How to Wire a 20A/250V, NEMA 2-20 Non-Grounding Receptacle | Impedance Analysis | Voltage Divider Rules Quiz