NEMA TT-30 / 50A Shore Power

North American campgrounds standardise on two pedestal receptacles, both defined by NEMA (National Electrical Manufacturers Association) configuration codes: TT-30R (30A, one hot leg at 120V, twist-lock) and 14-50R (50A, two hot legs each at 120V — 240V split-phase — plus neutral and ground). A third option, ordinary household NEMA 5-15 or 5-20 (15A/20A, 120V), appears at overflow sites, private driveways, and some state parks with no dedicated RV hookup.

The most common misconception is that TT-30 supplies '30A at 240V'. It does not: TT-30 carries a single 120V leg, so its real capacity is 30A × 120V = 3,600W. The '30A' rating some people generalise into '240V-class power' is simply wrong — there is no second hot leg on this receptacle at all.

The 14-50 pedestal is the mirror-image mistake: because it is rated 50A, it looks like a modest step up from TT-30, but each of its two hot legs independently carries up to 50A at 120V. A rig with a 50A/125-250V split-phase panel can therefore draw up to 12,000W combined (2 × 50A × 120V) — four times the real capacity of a TT-30 pedestal, not the ~67% increase the amperage numbers alone would suggest.

Adapters — commonly called 'dogbones' from their two-ended shape — step a plug between these standards: 30A-to-50A (to use a 30A-corded rig on a 50A pedestal, which simply wastes the second leg), 50A-to-30A (to run a 50A rig on a 30A pedestal, capped at the pedestal's real 3,600W), and 15/20A-to-30A for household outlets. Each adapter only changes the physical connector — it does not change the amperage a circuit or shore cable can safely deliver. Forcing a plug that does not natively match the pedestal risks bending or breaking blades, defeating the ground/neutral bonding the pedestal receptacle is wired for, and overloading a lighter-gauge cable or the pedestal's own breaker; the correct adapter, not force, is what NEC Article 551 and RV manufacturers' documentation both call for at RV sites.