Adding a 48A EVSE to an Existing 200A Dwelling Service
An existing 2,100 sq ft single-family dwelling has a 200A, 120/240V single-phase service. The calculated existing load includes 3 VA/sq ft general lighting, two 20A small-appliance circuits, one 20A laundry circuit, an 8 kW electric range, a 5 kW dryer, a 4.5 kW water heater, and a 3-ton heat pump with 10 kW electric auxiliary heat. The owner wants to add a hardwired 48A EVSE in the attached garage. The contractor proposes to keep the 200A service and add a 60A breaker, arguing that the EVSE only draws 48A and the service is '200A.' The utility transformer is 25 kVA. The inspector has one year of utility demand data showing a peak demand of 14.2 kVA. The question is whether the service is adequate and what alternatives exist if it is not.
1. Using the NEC optional method for a dwelling, estimate whether the 200A service can carry the added 48A EVSE. State assumptions.
Read the worked answer
Use 220.82. General lighting: 2,100 sq ft x 3 VA = 6,300 VA. Small-appliance: 2 x 1,500 = 3,000 VA. Laundry: 1,500 VA. Subtotal = 10,800 VA. Apply 100% of the first 10,000 VA plus 40% of the remainder: 10,000 + 0.40(800) = 10,320 VA.
Add the range at 8,000 VA, dryer at 5,000 VA, water heater at 4,500 VA, and heating at 10,000 VA. The 48A EVSE is a continuous load: 48A x 240V = 11,520 VA; at 125% = 14,400 VA.
Total = 10,320 + 8,000 + 5,000 + 4,500 + 10,000 + 14,400 = 52,220 VA. A 200A service at 240V has 48,000 VA capacity. By the optional method, the service is about 4,220 VA short, so the 200A service is not adequate unless a load-management or existing-demand method is used.
The assumption is that the heating load is taken as the 10 kW auxiliary heat; adding the heat-pump compressor would only increase the total.
2. What code-compliant alternatives would you accept if the calculated load exceeds the service rating?
Read the worked answer
Accept one of the following, supported by a load calculation:
- A service upgrade to 320A/400A, with a new meter socket, service conductors, and panel rated for the load.
- An energy management system under Article 750 that limits the EVSE or the 10 kW auxiliary heat so the calculated load remains within 48,000 VA. The control must be listed and set so the loads cannot operate simultaneously.
- A lower-amperage EVSE. A 40A EVSE requires a 50A circuit and is calculated at 12,000 VA; a 32A EVSE requires a 40A circuit and is calculated at 9,600 VA. Recalculate the service each time.
- The 220.87 existing-demand method using the one-year peak of 14.2 kVA. Under 220.87, use 125% of the maximum demand plus the new load: 14.2 x 1.25 = 17.75 kVA; 17.75 + 14.4 = 32.15 kVA, below 48,000 VA. Require the utility data and confirm no planned load growth.
Do not accept simply adding a 60A breaker without a load calculation.
3. Size the branch-circuit conductors and overcurrent device for the 48A EVSE. What additional protection does Article 625 require?
Read the worked answer
The 48A EVSE is a continuous load. 625.42 requires the branch circuit to be sized at 125% of the maximum load: 48A x 1.25 = 60A. Use a 60A branch circuit and a 60A overcurrent device.
For copper conductors, 6 AWG THHN/THWN at the 75°C termination rating has 65A ampacity and is acceptable for a 60A circuit. 6 AWG NM-B is limited to 55A at 60°C and is not acceptable for a 60A circuit unless the EVSE load is reduced. The equipment grounding conductor for a 60A circuit is 10 AWG copper under Table 250.122.
Article 625 also requires the EVSE to be listed and installed per its instructions. GFCI protection is required for receptacles installed for EV charging under 625.54; a hardwired EVSE follows its listing, and many units include a listed CCID. Provide a disconnect means if required by the installation instructions or local rules, and verify the panel busbar and feeder are rated for the added 60A circuit.