How many amps does your home actually need?
The 100A vs 200A vs 400A question used to be easy. EV charging, heat pumps, induction cooking, and tankless water heaters changed the math. Here's how we size service for Marin homes in 2026.
By Steven Lockhart · Reviewed by Alex Towery, C-10 #989290
Updated 2026-06-16
Most Marin homes built before 1990 have 100A or 125A service — adequate for the loads of that era but increasingly stretched by modern electrification. Today's typical answer is 200A for most homes, 400A for larger homes (3,500+ sq ft) or homes adopting multiple electrification upgrades simultaneously (EV, heat pump, induction range, electric dryer, electric water heater). Upgrading service is a one-time cost that prevents repeat panel work over the next 15-20 years.
01What service amperage actually means.
Service amperage is the capacity of the electrical service entering your home — the cable from the utility transformer, through the meter, into the main panel. A 200A service can deliver up to 200 amps of current at 240V (about 48,000 watts of total household capacity). A 100A service tops out at 24,000 watts. The number is the ceiling — your actual usage is almost always well below it, but the ceiling matters when adding major loads.
Three things drive the right sizing: peak instantaneous demand (what loads run simultaneously at the worst case), connected load (the sum of all circuit ratings, which NEC uses for calculations), and growth headroom (what you might add in the next 10-15 years). Most modern homes need 200A for comfortable headroom; larger homes or aggressive electrification need 400A.
02When 100A is enough — and when it isn't.
100A service was the residential standard from 1950-1990. It can still work for some homes today, but the constraints have tightened.
When 100A still works
Small homes (under 1,500 sq ft) with gas appliances throughout (gas range, gas water heater, gas furnace), no EV charger, no plans for electrification, and modest electric loads (lighting + electronics + small appliances). About 15-20% of Marin homes we see fit this profile.
When 100A is at its limit
Larger homes (1,500-2,500 sq ft) with mixed gas/electric appliances, occasional EV charging via NEMA 14-50 outlet, electric dryer. Service capacity is technically adequate per NEC load calc, but headroom for any additions is essentially zero.
When 100A no longer works
Homes adding EV chargers (especially 40A+ Level 2), heat pumps, induction ranges, or electric water heaters. The math just doesn't work — the new loads exceed the available capacity even with conservative load calculations. Service upgrade required before new loads can be added.
03Why 200A is the modern default.
For new construction and major remodels in Marin, 200A is now the standard service size. The math is straightforward: a typical 2,000-2,800 sq ft home with electric range, electric dryer, electric water heater, heat pump HVAC, and one Level 2 EV charger calculates to around 110-140A peak demand under NEC load calculation rules. Adding a second EV charger or upgrading to faster Level 2 charging pushes that toward 160A. 200A service provides comfortable headroom for that load profile plus 15-20 years of growth.
From a cost perspective, the upgrade from 100A to 200A during a panel replacement is incremental — typically $2,000-$3,500 above the cost of a like-for-like 100A replacement. The same upgrade done later as a separate project costs $6,000-$8,500 (because PG&E coordination, permits, and the service drop work all have to happen again). Doing the upsize during initial replacement is dramatically cheaper than deferring it.
04When 400A makes sense.
400A service is the right answer for larger homes, estates, or aggressive electrification profiles. Here's when we recommend it:
| Home profile | Why 400A | Typical Marin cost premium |
|---|---|---|
| 3,500-5,000 sq ft home, fully electric | 200A is at calculated limit; 400A gives headroom | +$3,500 – $5,500 over 200A install |
| Estate (5,000+ sq ft) with detached structures | Detached ADU, pool house, garage — distributed loads | +$5,500 – $9,500 over 200A install |
| Multi-EV households (3+ Level 2 chargers) | Multiple chargers exceed 200A capacity | +$4,000 – $6,500 over 200A install |
| Home + dedicated workshop with welding/machining | Workshop heavy loads on dedicated panel | +$3,500 – $6,000 over 200A install |
| Solar + battery + EV + heat pump combination | Combined load + production capacity benefits from 400A | +$3,500 – $5,500 over 200A install |
Not sure whether 200A or 400A is right for your specific home and electrification plans? A 30-minute load study gives you the actual numbers.
Request a load studyCommon questions.
How do I know how much service amperage I currently have?
Two places to check: the meter base (outside, where PG&E's service enters the home) often has the amperage stamped on the front, and the main breaker inside the panel will be labeled with its amperage rating (usually '100', '150', '200', etc. printed on the breaker handle). If you can't find the rating, send us a photo and we'll identify it.
Can I upgrade from 100A to 200A without changing my main panel?
Almost never. The main panel and the main breaker are sized to the service capacity, so upgrading service amperage requires upgrading both. The typical scope is panel replacement + service-side work (mast, weatherhead, service entrance conductors) + PG&E coordination, all together. Trying to upgrade just the service without the panel almost always creates code compliance issues.
Do I need a permit for a service upgrade?
Yes — every service-side change requires an electrical permit from the local AHJ (Authority Having Jurisdiction). In Marin, that's typically the city building department or Marin County for unincorporated areas. Service upgrades also require PG&E coordination since they involve their meter and service drop. We handle both permit filing and PG&E coordination as part of every service upgrade we do.
How long does a service upgrade take?
From contract signing to PG&E re-energization: typically 4-8 weeks. The bulk of calendar time is PG&E coordination (3-5 weeks for them to schedule the cut-in) and permit issuance (1-2 weeks). Install day itself is 6-10 hours during which power is off — we coordinate that window with your schedule and PG&E's. We give a written timeline at contract signing.
Is 400A service overkill for most homes?
For typical 2,000-3,000 sq ft Marin homes with normal electrification (one EV, heat pump, electric dryer): yes, 200A is the right answer. 400A is meaningful upgrade for larger homes (3,500+ sq ft), estate properties with detached structures, multi-EV households, or any home where the combined electrification load pushes calculated demand above ~160A. We do the load study and tell you honestly which is right for your situation.
How do you handle pricing — flat fee or hourly?
Both, depending on scope. Routine service calls and predictable scope (panel replacement, EV charger install, transfer switch install, fixture replacement) are flat-fee quoted up front. Diagnostic visits and emergency scope are hourly because we don't know what we'll find. Either way, you get a written quote before work starts on anything significant, and we don't proceed beyond the quote without your sign-off.
How quickly can you schedule?
Depends on scope and season. Emergency dispatch: same-day across Marin County (1-3 hours business hours, 1-4 hours after-hours). Same-day standard service: 3-6 hours from call when capacity allows; otherwise next business day. Scheduled service work: 1-3 weeks typical. Larger projects requiring permits and PG&E coordination: 4-12 weeks depending on scope. We're upfront about timeline at the quote stage.
What warranty do you offer on work?
Our standard residential warranty: 2 years on labor, manufacturer warranty on parts (varies by product — typically 1-10 years). Major installs (panels, generators, EV chargers) often have longer manufacturer warranties (5-10 years). If there's an issue with our work in the warranty period, we come back and fix it at no cost. We also stand behind work past warranty — repeat customers and referrals matter more than a transactional fix.
Are you licensed and insured?
Yes. California State License Board C-10 Electrical Contractor #989290, in good standing. Carry general liability insurance and workers' compensation insurance as required by California law. Bondable on projects requiring it. Happy to provide proof of insurance to clients or property managers on request. License lookup: cslb.ca.gov.
Talk to a licensed electrician in Marin.
Family-run, C-10 #989290, 20+ years in the trade. Honest scoping, fair pricing, work that lasts.