Licensed Electrical Contractor Branch Circuit Calculations 2

Question 1

A 20-ampere branch circuit serves a small appliance circuit in a kitchen. What is the maximum load, in watts, allowed on this circuit at 120V using the 80% rule?

Accepted Answer

1,920 watts

Answer

The 80% continuous load rule limits a 20A circuit at 120V to 20A × 0.80 × 120V = 1,920 watts.

Question 2

Per NEC Article 210, how many small appliance branch circuits are required for the kitchen countertop receptacle outlets in a dwelling unit?

Accepted Answer

At least two 20-ampere circuits

Answer

NEC 210.11(C)(1) requires at least two 20-ampere small appliance branch circuits for kitchen countertop receptacles.

Question 3

A branch circuit conductor must be sized so that voltage drop does not exceed what percentage for branch circuits per NEC recommendations?

Accepted Answer

3%

Answer

The NEC recommends (informational note) that voltage drop on a branch circuit not exceed 3% for best performance.

Question 4

What is the minimum wire gauge (AWG) required for a 20-ampere, 120V branch circuit using copper conductors?

Accepted Answer

12 AWG

Answer

NEC 240.4(D) requires 12 AWG copper conductors for circuits protected by 20-ampere overcurrent devices.

Question 5

A branch circuit supplies a 7.5 kVA, 240V single-phase motor load. What is the full-load current of this motor?

Accepted Answer

31.25 amperes

Answer

I = kVA × 1000 / V = 7,500 / 240 = 31.25 amperes for a single-phase load.

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Licensed Electrical Contractor Branch Circuit Calculations 2