CME Advanced Load Calculations 2

Question 1

A 3,600 sq ft dwelling has a 12 kW range. Using the NEC Table 220.55 demand factor, what is the demand load for the range?

Accepted Answer

8,400 W

Answer

NEC Table 220.55 for a single range rated 12 kW (over 8.75 kW) uses Column C: 8 kW + 5% per kW over 12 kW, but for exactly 12 kW the demand is 8,400 W per the note (8 kW + 400 W).

Question 2

When calculating the demand load for electric dryers in a multi-family building with 25 units, which NEC table applies?

Accepted Answer

Table 220.54

Answer

NEC Table 220.54 provides demand factors for household electric dryers in multi-family and similar installations.

Question 3

A commercial building has a 200 kVA transformer supplying a 208Y/120V panel. What is the maximum continuous load in amps at 208V three-phase?

Accepted Answer

555 A

Answer

I = kVA × 1000 / (V × √3) = 200,000 / (208 × 1.732) = 200,000 / 360.3 ≈ 555 A.

Question 4

Per NEC 220.82, the optional calculation method for dwelling units applies when the service or feeder does NOT exceed:

Accepted Answer

200 amperes

Answer

NEC 220.82 optional method is available for dwelling units served by a single 3-wire, 120/240V or 208Y/120V service of 100 A or greater — the section covers existing or new 100 A+ services but is commonly applied up to 200 A service entries.

Question 5

A 480V, 3-phase motor has a nameplate full-load current of 40 A. What minimum feeder ampacity is required per NEC 430.22 for a single motor?

Accepted Answer

50 A

Answer

NEC 430.22 requires the feeder to be sized at 125% of the motor FLC: 40 A × 1.25 = 50 A.

(CME) Certified Master Electrician Practice Test

(CME) Certified Master Electrician Practice Test

CME Advanced Load Calculations 2