200A vs 400A vs 320A Service Upgrade Decision Matrix

Why this matters

The conversation about service size has shifted in the last five years. EV charging, heat-pump conversions, induction ranges, electric water heating, and battery storage now drive load calculations that 100 A and even 200 A services no longer cover at the standard demand factors. The decision among 200 A, 320 A (a meter-base rating that combines two 200 A panels for 400 A total), and a true 400 A service hinges on the NEC 220 load calc, the utility's available drop capacity, the panel real estate the customer has for 24-36 months of future loads, and the cost of doing it twice. A senior electrician makes this call from a documented load calc, not from a homeowner's wish list. The matrix below is how that decision actually gets made in the field.

When 200 A still wins

A 200 A service is still the right answer for the household that meets all of the following: NEC 220 calculated load under 160 A (80 percent of 200), one Level 2 EV charger or none, gas or oil heat (not heat pump), gas water heater or one electric tank, no plans for battery storage in the next 5 years, and adequate breaker positions in the existing 200 A panel for at most one additional dedicated circuit. Cost discipline matters: a 200 A upgrade is the simplest permit and the shortest utility-coordination window, and re-doing it 5 years later if loads grow is the cost of conservatism.

When 320 A is the sweet spot

A 320 A meter base feeds two 200 A panels (a 200 A main service panel and a 200 A subpanel, or two 200 A main lug-only panels through a single meter-main combo). It is the field-probability winner for the homeowner who is mid-electrification: one EV charger today plus space for a second, planning a heat-pump conversion, considering induction in the next 24 months, considering battery storage but not certain. The 320 A meter base provides the headroom while keeping each panel at the 200 A class - which means standard 200 A panels, 200 A breakers, and most importantly the utility's standard residential meter socket. Most U.S. utilities have a published residential service tariff that goes to 320 A on a single-meter residential socket without requiring CT (current transformer) metering. CT metering is the cost cliff at the 400 A line.

When 400 A is the right answer

A true 400 A service crosses into commercial-class equipment. The customer who needs it: NEC 220 calculated load above 280 A (80 percent of 400 A would be 320, but the calc lives at the demand-factor result), a large electric heat-pump system with backup electric resistance, two EV chargers at 80 A each, a battery storage system above 30 kW continuous, accessory dwelling unit (ADU) feeding off the main service, or a large workshop with welding or 3-phase equipment. The 400 A service typically requires CT metering at the utility level, which the utility installs separately from the homeowner's service entrance and which the homeowner usually pays a higher monthly tariff for. The service-entrance conductor jumps to 600 kcmil aluminum or 500 kcmil copper per NEC Chapter 9 Table 310.16 / 310.5(B) ratings, the meter base and service disconnect become substantially larger, and the panel real estate now supports a 42-position main with a 200 A subpanel for future loads.

Load calculation gates the decision

Run the NEC 220 standard calc OR the NEC 220.83 optional method for existing dwellings. The optional method credit for the first 10 kVA and 40 percent of the remainder usually produces a smaller number than the standard calc and is the basis a utility will accept for a residential service upgrade. Do not skip the calc - a service quoted on a homeowner's "I think we need 400 amps" without a documented calc is how electricians end up upgrading twice. Attach the calc to the permit application and keep a copy in the job folder.

EV charger load specifically: NEC 625.42 allows EVSE load management (load-shedding) to count the charger at its managed maximum, not its connector rating. A 48 A EV charger managed to 24 A counts as 24 A in the load calc. This single rule has saved more 200 A services from upgrade than any other code change in the last 5 years, and is a separate decision matrix worth running before deciding the service size.

Utility coordination gates the decision

Call the utility's planning desk BEFORE quoting the upgrade. The drop, transformer, and primary feeder from the pole to the meter have a published rating. Some neighborhoods are on shared-transformer service where the existing transformer cannot support a 400 A house addition without a transformer upgrade - which the utility may charge the customer for, or may decline to do without an aggregator-level rebuild. The utility will tell you what the drop will support; quote the upgrade to match what the utility will deliver, not what the customer requests in isolation.

Cost ladder and timing

In ascending dollar order, NOT including local labor variation: 200 A upgrade with new meter base, new service-entrance conductor, new main panel, new grounding electrode system, AHJ permit, utility re-connect. 320 A upgrade adds a larger meter-main combo and either a second 200 A panel or a 200 A subpanel feeder. 400 A upgrade adds a CT-metered enclosure, separate utility CT can, larger service-entrance conductor (600 kcmil class), upsized GES per NEC 250.66, and a substantially larger main panel or paralleled mains. Timing: 200 A and 320 A typically clear permit and utility in 2-4 weeks; 400 A with CT metering often runs 8-12 weeks because the utility's engineering review is on a slower track.

Decision rules at a glance

Calculated load under 160 A, gas heat, one or zero EVSE - choose 200 A.

Calculated load 160-220 A, electrification in progress, single-meter residential tariff available - choose 320 A.

Calculated load above 220 A, multiple high-amp loads (heat pump + two EVSE + battery), CT metering accepted by the utility - choose 400 A.

When in doubt and the utility supports 320 A on a residential tariff: 320 A almost always beats 200 A on lifetime cost without crossing the CT-metering threshold.

References

• NEC 2023 Article 220 - Branch-Circuit, Feeder, and Service Calculations (specifically 220.83 optional method)
• NEC 2023 Article 230 - Services (service-entrance conductor sizing)
• NEC 2023 Article 250.66 - Grounding Electrode Conductor sizing
• NEC 2023 Article 625.42 - EVSE load management
• NEC 2023 Chapter 9 Table 310.16 and Table 8 - Ampacity and conductor properties