Inside a breaker panel — main breaker, single-pole vs double-pole circuits
One slot = 120 V. Two slots (double-pole) = 240 V — that's why every big appliance breaker is a double. The main breaker at top is the service rating.
What this diagram shows
A simplified electrical panel: the main breaker at the top sets the service size, for example 200 amps. Below it, branch breakers snap onto two hot bus bars: single-pole breakers occupy one slot and serve 120-volt circuits like lights and receptacles, while double-pole breakers span two slots to capture both hot legs and serve 240-volt circuits like dryers, ranges, EV chargers, and hot tubs. Neutral and ground bars along the side terminate the white and bare conductors.
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Breaker Size Calculator
What size breaker do you need? Free NEC calculator from amps or watts — 125% continuous rule, standard 240.6(A) ratings, and the wire it must pair with.
