100 Amp vs.
200 Amp Panel

The difference between a 100A and 200A electrical panel determines whether your home can support solar, battery backup, and EV charging — and how safely it can do so. Here's the complete technical breakdown for Fresno, Clovis, and Madera homeowners.

Panel Upgrade Services (559) 355-1025

What "Amps" Actually Means for Your Home

Your electrical service amperage is the maximum rate at which electricity can flow from the utility into your home. A 100A service can deliver up to 100 amps at 240 volts — about 24,000 watts (24 kW) of total capacity. A 200A service doubles that to 48,000 watts (48 kW).

In practice, you can't use 100% of your service capacity continuously. The National Electrical Code (NEC) requires that continuous loads not exceed 80% of circuit capacity. So a 100A service provides about 80A (19.2 kW) of usable continuous capacity, and a 200A service provides about 160A (38.4 kW).

For homes built before 1990 in Fresno, Clovis, and Madera, 100A service was the standard. It was adequate for the appliances of that era. Today's energy demands — central air conditioning, electric vehicles, solar systems, and battery backup — require more capacity than a 100A panel can reliably provide.

Load Calculation: Does Your 100A Panel Have Room?

Here's a typical load calculation for a Fresno home with a 100A panel. The NEC Article 220 standard method calculates the minimum service size required for a home's loads:

Load	Typical Amperage	Notes
General lighting & outlets (1,500 sq ft)	30A	NEC: 3VA/sq ft × 1,500 = 4,500VA ÷ 240V = 18.75A, rounded up
Central AC (3-ton)	30–40A	Most common size in Fresno homes
Electric water heater	20–25A	Typical 240V/4,500W element
Electric range/oven	30–50A	Varies by appliance
Clothes dryer	20–30A	Typical 240V dryer
Refrigerator + misc kitchen	10–15A	Multiple 120V circuits
TOTAL (typical Fresno home)	~140–160A	Already exceeds 100A service
EV charger (Level 2, 50A circuit)	+50A	Requires dedicated circuit
Solar backfeed (10 kW system)	+40A	NEC 120% rule limits this on 100A panel

This is a simplified illustration. Actual load calculations use NEC Article 220 demand factors. Contact us for a site-specific assessment.

The NEC 120% Rule: Why It Limits Solar on 100A Panels

NEC Section 705.12 governs how solar systems connect to your main panel. The rule states: the sum of the main breaker amperage and the solar backfeed breaker cannot exceed 120% of the panel's busbar rating.

100A Panel

Limited

→100A main breaker

→100A busbar

→100A × 120% = 120A max

→120A − 100A = 20A max solar backfeed

→~4–5 kW maximum solar system

200A Panel

Recommended

→200A main breaker

→200A busbar

→200A × 120% = 240A max

→240A − 200A = 40A max solar backfeed

→~10–12 kW maximum solar system

What a 200A Panel Upgrade Enables

Full-size solar system

8–12 kW system sized to offset your actual PG&E usage — not a 4 kW system that barely makes a dent.

Home battery backup

Tesla Powerwall, Enphase IQ Battery, or Franklin WH aPower — all require adequate panel capacity.

Level 2 EV charging

Dedicated 50A circuit for a Level 2 charger. Impossible on most loaded 100A panels.

Future electric appliances

Heat pump HVAC, induction range, heat pump water heater — all require capacity that 100A panels often can't provide.

Safety margin

A 200A panel running your current loads operates at 50–60% capacity — well within safe limits. A 100A panel running the same loads is at 80–90% — at its limit.

Home value

A 200A panel is a documented upgrade that increases home value and simplifies future sale — especially with solar.

Frequently Asked Questions

Can I install solar on a 100 amp panel in Fresno?

Yes, but with significant limitations. The NEC 120% rule limits your solar backfeed breaker to 20A on a 100A panel (100A × 120% = 120A busbar max, minus 100A main = 20A backfeed). That supports roughly a 4–5 kW solar system — too small to meaningfully offset most Fresno homes' usage. A 200A upgrade is recommended for any system over 5 kW.

How much does a 200 amp panel upgrade cost in Fresno?

Cost depends on your current service size, meter location, and whether a utility service upgrade is needed. We provide a free, itemized quote. Contact us to schedule a free assessment.

How long does a panel upgrade take in Fresno?

The physical work takes 1 day. Permitting with the City of Fresno adds 2–3 weeks. PG&E service upgrade coordination adds 1–2 weeks. Total timeline from contract to completion is typically 3–5 weeks.

Do I need a permit for a panel upgrade in Fresno?

Yes. Panel upgrades in Fresno require a permit from the City of Fresno Development and Resource Management Department. We handle all permit filings and schedule the final inspection — you don't deal with the city.

What is the NEC 120% rule for solar panels?

The NEC 120% rule (NEC 705.12) states that the sum of the main breaker amperage and the solar backfeed breaker cannot exceed 120% of the panel's busbar rating. For a 200A panel with a 200A main breaker and a 200A busbar: 200A × 120% = 240A maximum. 240A - 200A main = 40A maximum solar backfeed breaker, supporting approximately 10–12 kW of solar.

Can I add a subpanel instead of upgrading my main panel?

A subpanel adds circuits but doesn't increase your total service capacity. If your 100A service is already loaded, adding a subpanel doesn't solve the capacity problem — it just moves it. A service upgrade (replacing the 100A service with 200A) is the correct solution when capacity is the issue.