Square D 30-Amp Fusible Metallic Disconnect at Lowes The Square D by Schneider Electric 30 amps 120 volts 2 pole light duty safety switch is designed for residential and agricultural applications in disconnecting power to workshops, hobby rooms, furnaces and garages. 3-wire design with 2 blades and fuse holders and 1 How to Wire a Square D Panel | Hunker Only Square D style circuit breakers fit in a Square D style panel box. Square D circuit breakers and panels use a square with a capitol D inside as an identification marker. Three wires enter a residential Square D service panel from the electric meter; two 120-volt hot wires and a neutral. These wires connect to bus bars.