Adding a 48 A EVSE to a 100 A Service: Does It Fit?
A homeowner with a 1,800 ft² single-family house has a 120/240 V, 100 A overhead service and a 24-space panel with two open spaces. Existing major loads are a 12 kW electric range, a 5 kW clothes dryer, a 4.5 kW water heater, and a 3-ton air conditioner whose nameplate reads 22 A at 240 V. The general lighting load is figured at 3 VA/ft², along with the two small-appliance circuits and one laundry circuit. The owner wants a hardwired 48 A EVSE installed in the attached garage, 15 ft from the panel along the garage wall. The house was built in 1998 with copper NM-B wiring throughout. The owner has budget for the charger but not for a service change and asks whether the existing service "has room."
1. Using the optional method of 220.82, does the existing 100 A service have capacity for the 48 A EVSE? Show the calculation and state your conclusion.
Read the worked answer
General loads (220.82(B)): lighting 1,800 ft² × 3 VA = 5,400; small appliance 3,000; laundry 1,500 → 9,900 VA.
Appliance/other loads:
- Range 12 kW → 8,000 VA (Table 220.55, Column C for one range ≤12 kW)
- Dryer → 5,000 VA (Table 220.54, 5 kW minimum)
- Water heater → 4,500 VA
- EVSE 48 A × 240 V → 11,520 VA
Subtotal: 9,900 + 8,000 + 5,000 + 4,500 + 11,520 = 38,920 VA Apply 220.82(B): 10,000 + 0.40 × 28,920 = 21,568 VA
Add largest of heating/cooling (220.82(C)): A/C 22 A × 240 V = 5,280 VA → 26,848 VA Demand: 26,848 ÷ 240 = 111.9 A
Conclusion: No. The calculated demand exceeds the 100 A service even with the EVSE taken at 100% of nameplate; using 125% for the continuous EVSE load (14,400 VA) pushes it to about 117 A. The minimum compliant service is 125 A, and 200 A is the practical choice. Note 220.82 is permissive - a 220.87 calculation using 30 days of utility demand data could be used to verify actual existing demand, but the standard calculation fails.
2. Assuming the service is upgraded, specify the EVSE branch circuit: circuit rating, overcurrent device, conductor type and size for a 15 ft run, and the GFCI/disconnect requirements that apply.
Read the worked answer
Circuit rating: EVSE loads are continuous, so 48 A × 1.25 = 60 A → a 60 A branch circuit with a 60 A overcurrent device.
Conductors:
- In raceway with 6 AWG Cu THWN-2: 65 A at the 75 °C column - adequate (terminations must be 75 °C rated).
- If NM-B is used: 334.80 limits the ampacity to the 60 °C column, where 6 AWG = 55 A. That is not enough for a 60 A circuit, so 4 AWG NM-B (70 A at 60 °C) would be required, or run conduit with THHN/THWN-2.
- EGC: 10 AWG Cu (Table 250.122 for a 60 A device).
Disconnect: 625.43 requires a disconnecting means only for EVSE rated over 60 A or over 150 V to ground; a 48 A, 240 V unit does not require a separate disconnect, but the breaker must be capable of being locked open (625.23).
GFCI: Edition-dependent - the 2020 NEC requires GFCI protection for receptacles supplying EVSE (625.54), while the 2023 NEC extends it to the outlet itself, which would require a GFCI breaker on a hardwired unit. Confirm the edition Utah has adopted before choosing the breaker.
3. The owner cannot afford a service upgrade. What code-recognized options remain, and which would you reject?
Read the worked answer
First, quantify the headroom without the EVSE: 9,900 + 8,000 + 5,000 + 4,500 = 27,400 → 10,000 + 0.40 × 17,400 = 16,960; plus A/C 5,280 = 22,240 VA = 92.7 A. The spare capacity is roughly 7 A at 240 V - around 1.7 kW.
Options that are code-recognized:
- 625.42 energy management system. A listed EMS that limits the EVSE draw lets the branch circuit and feeder be sized to the controlled maximum rather than the nameplate. This is the realistic path to meaningful Level 2 charging.
- 220.87 existing-load verification. Thirty days of demand data (15-minute peak) plus 125% of the new load, if it stays within the service rating.
- A much smaller unit. Even a 16 A/240 V EVSE (3,840 VA) lands at about 99 A - barely inside the 100 A service. Anything larger fails the standard calculation.
Reject: Installing the 48 A unit and simply relying on "two open spaces in the panel," upsizing the main breaker without recalculating, or assuming the A/C and the charger never run together. Panel space says nothing about service capacity, and 240.4/230.42 require the service and feeder to carry the calculated load.