EVITP Load Calculations and Service Capacity Assessment — Questions and Answers
Question 1: An EVSE draws a maximum of 40 A. Under NEC 625, what is the minimum overcurrent protective device rating for its branch circuit?
- 40 A
- 45 A
- 50 A (Correct answer)
- 60 A
Correct answer: 50 A
The NEC treats EV charging as a continuous load, so the overcurrent device must be at least 125% of the maximum load: 40 A × 1.25 = 50 A.
Question 2: A Level 2 charger runs at 240 V and 32 A. About how much power does it deliver?
- 3.8 kW
- 7.7 kW (Correct answer)
- 9.6 kW
- 11.5 kW
Correct answer: 7.7 kW
Power = voltage × current: 240 V × 32 A = 7,680 W, or about 7.7 kW.
Question 3: In a dwelling-unit load calculation under the 2023 NEC (220.57), what load must you use for EVSE?
- 5,000 W or the nameplate rating, whichever is larger
- 7,200 W or the nameplate rating, whichever is larger (Correct answer)
- The nameplate rating only
- 80% of the nameplate rating
Correct answer: 7,200 W or the nameplate rating, whichever is larger
NEC 220.57 sets the EVSE load at 7,200 W (volt-amperes) or the equipment's nameplate rating, whichever is larger.
Question 4: A 60 A circuit supplies a hardwired EVSE with an adjustable current setting. What is the highest continuous charging current you can set?
- 60 A
- 54 A
- 50 A
- 48 A (Correct answer)
Correct answer: 48 A
A continuous load may not exceed 80% of the overcurrent device rating, which is the inverse of the 125% rule. 60 A × 0.8 = 48 A.
Question 5: You want to add EVSE to an existing commercial service. Which NEC method lets you size the added load from the facility's measured maximum demand?
- NEC 220.87, using a year of maximum demand data or a 30-day recording at 15-minute intervals (Correct answer)
- NEC 230.42, using the service conductor ampacity only
- NEC 625.17, using the cord length
- NEC 110.26, using working clearances
Correct answer: NEC 220.87, using a year of maximum demand data or a 30-day recording at 15-minute intervals
NEC 220.87 lets you determine existing load from real maximum demand data: one year of utility data, or a 30-day recording at 15-minute intervals if utility data isn't available. You then add the new EVSE load.
Question 6: Several EV chargers are controlled by an automatic energy management system (EMS). How does the NEC let you calculate their load on the feeder or service?
- Use the sum of all EVSE nameplate ratings regardless of the EMS
- Use the maximum load the EMS allows (Correct answer)
- Ignore EVSE load entirely
- Use 50% of total nameplate ratings
Correct answer: Use the maximum load the EMS allows
Under NEC 625.42 and Article 750, when an EMS limits the load, the calculated load can be the maximum value the EMS permits instead of the sum of the nameplate ratings. This can avoid a service upgrade.
