Service Upgrade for a 2,400 sq ft Dwelling (and the EV Charger That Comes Later)
This is a service replacement for a 2,400 sq ft single-family dwelling with a 240/120 V single-phase service. Connected loads are: one 12 kW electric range (nameplate rating), a 5,000 W electric clothes dryer, a 4,500 W storage-type water heater, a 1,200 VA dishwasher, a 15 kW electric furnace, and a 5 kW central air conditioner that is interlocked so it never runs at the same time as the furnace. The kitchen has two small-appliance branch circuits and there is one laundry circuit. There are no other major appliances. The owner asks whether a 200 A service is adequate and what would happen if a 48 A, 240 V EV charger were added on a dedicated hardwired circuit next year. All service and feeder conductors are copper with 75°C terminations.
1. Compute the demand load for general lighting, the small-appliance circuits, and the laundry circuit, and state the total service demand in volt-amperes.
Read the worked answer
General lighting: 2,400 sq ft x 3 VA/sq ft = 7,200 VA
Small appliance: 2 circuits x 1,500 VA = 3,000 VA
Laundry: 1,500 VA
Subtotal = 7,200 + 3,000 + 1,500 = 11,700 VA
Apply the dwelling demand factors (first 3,000 VA at 100%, remainder at 35%):
- 3,000 VA x 1.00 = 3,000 VA
- (11,700 - 3,000) = 8,700 VA x 0.35 = 3,045 VA
Answer: 6,045 VA.
This is the figure carried into the service calculation. Note that the demand factor is applied here, not to the individual appliance loads that follow.
2. Complete the service calculation and determine the minimum service rating.
Read the worked answer
| Load | VA |
|---|---|
| Lighting/SAA/laundry (demanded) | 6,045 |
| Range, 12 kW (demand table, one range) | 8,000 |
| Dryer (5,000 W minimum) | 5,000 |
| Water heater | 4,500 |
| Dishwasher | 1,200 |
| Heating (larger of heat 15,000 vs. A/C 5,000) | 15,000 |
| Total | 39,745 |
Heating and cooling are noncoincident, so only the larger is included.
39,745 VA / 240 V = 165.6 A
165.6 A exceeds 150 A, so the next standard service rating applies: 200 A service.
Judgment point: a 150 A service would be undersized even though the calculated load is only 16 A above it - the load is continuous in character and there is no spare capacity for the future EV load.
3. The owner adds a 48 A, 240 V EV charger on a dedicated circuit. Does the 200 A service still comply, and what options exist?
Read the worked answer
The EV charger is a continuous load, so it must be taken at 125% for the branch circuit and for the service calculation:
- 48 A x 1.25 = 60 A
- 60 A x 240 V = 14,400 VA
New total = 39,745 + 14,400 = 54,145 VA
54,145 / 240 = 225.6 A -> the 200 A service is overloaded and does not comply.
Even taking the charger at its nameplate 11,520 VA, the total is 213.6 A, still over 200 A.
Options, in order of preference:
- Load management / energy management system on the EV branch circuit that limits total demand so the calculated load stays within 200 A - this is a code-recognized approach and usually the cheapest.
- Service upgrade to 320/400 A.
- Reduce the charger to a lower-current setting (e.g., 32 A or 40 A) and re-run the calculation.
- Field-verify an existing dwelling load using a measured-demand method (recording the actual demand over a representative period) if the calculated method is the only barrier - but this must reflect the actual occupancy, not a design assumption, and the EV load still gets added on top.
What is not acceptable: simply installing the charger because 'the main breaker rarely trips.'