What Is Considered Odd & Even in a Circuit Breaker Panel?

Power to the Panel

• The power company feeds an alternating current signal along the transmission lines stepped down by a transformer before being fed into a residential panel. Two hot wires -- at a voltage of 240 volts relative to each other -- connect to a pair of brass bus bars in the panel. A 120-volt circuit draws power from one or the other of these bars and is completed by a neutral wire leading back to the transformer. The bars are identical, and panel components are designed so circuit breakers make contact with only one of them.

Panel Design

• Although circuit breaker panel designs differ among manufacturers, the hot bus bars in all of them have a series of clips, each of which accepts a single breaker. The design is such that adjacent breakers are in contact with a different bar, which is necessary for supplying 240-volt power to large appliances. The breakers controlling 240-volt circuits come in pairs, and when you snap a paired breaker into the panel, each is automatically in contact with a different bar. The voltage between the wires connected to each breaker is at 240 volts relative to each other.

Odd and Even Bus Bars

• The odd bus bar in the panel is the one with the first clip. By convention, in a panel with vertical bus bars, the odd-numbered bus bar is the one on the left and accepts the topmost breaker. In a panel with horizontal bars, the odd-numbered bar is the top one, and the No. 1 clip is to the left. The No. 3 clip on the panel, which is adjacent to No. 1, connects to the opposite bus bar while the No. 2 clip, which is across from No. 1, connects to the same bus bar as No. 1.

Considerations

• Residential electricity is alternating current, and the two bus bars in the panel are 180 degrees out of phase. This means that when power flows in one direction, one bar is hot and the other neutral. When the polarity switches, which happens 60 times a second, the opposite is true. This isn't important for 120-volt wiring, and circuits can be added to the odd and even sides interchangeably. Any 240-volt circuits won't work properly, however, if you connect both hot wires to the same bus bar. Fortunately, panels and 240-volt paired breakers are designed so it's impossible to do this.