← Marine · Marine Electrical Systems
30A = 3,600W (30 × 120V). 50A = 12,000W (50 × 120V × 2 legs). Same math as RV shore power. Adapters only change plug shape—they don't add capacity. See the marine electrical systems guide for the full picture.
NFPA 70 and ABYC govern marine shore power installations. Same standards as RV: 30A and 50A service. Wattage math, adapter risks, and shore power breaker tripping boat issues apply identically.
| Service | Formula | Max Watts |
|---|---|---|
| 30A | 30 × 120V | 3,600W |
| 50A | 50 × 120V × 2 legs | 12,000W |
50A→30A adapter: your 50A boat is limited to 3,600W. Running dual AC, water heater, and charger will trip the breaker. Adapters don't increase capacity—they only adapt plug shape.
Reverse polarity, open neutral, voltage drop. Same as campgrounds. Use a marine surge protector or EMS to detect and block unsafe power. Cross-vertical: RV 30 vs 50 Amp.
30A = 3,600W (single AC, fridge, charger). 50A = 12,000W (dual AC, water heater, full galley). Same electrical math as RV.
Overload, voltage drop from long cord or bad marina wiring, or faulty appliance. Never upsize the breaker. Reduce load or fix wiring.
Yes, but you're limited to 3,600W. Running dual AC through an adapter will trip. The adapter only changes plug shape—it doesn't add capacity.
If you're diagnosing RV electrical or appliance problems, these guides may help:
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Last updated: March 2026 · Reviewed for technical accuracy