I started a simple project which has turned into a semi-major one. I recently purchased a home with a seperate building a couple hundred feet from the home. It started out with an outdoor light switch which would not click off most of the time. This switch has turned into replacement of the ancient fuse box sub-panel in the building. The sub-panel is fed with 3 wires from the main panel in the house; 2 hot and one neutral (grounded wire). After reading "Wiring Simplified" and numerous posts I have concluded that this installation requires 4 wires under today's NEC; 2 hot 1 neutral and 1 Gnd. The wiring from the house is in great shape and I am not going to replace the line from the house so I am limited with the 3 wires. The question is on bonding. Do I install the bonding screw and bond the neutral bus bar, the ground rods, and the ground bus bar together? Or do I leave the bonding screw out and just connect the ground bus bar to the ground rods and leave the neutal bus bar just connected to the neutral from the house? The old sub-panel had the neutral, the ground and the grounding rod bonded. For right now I am hooking it up the same as previously.
Thanks in advance for any feedback.
You are confused. A 4-wire setup is not required to detached structures UNLESS you have other metallic paths between the house and the detached structure like phone lines, metallic gas/water lines, etc. With your 3 wire feeder, you absolutely need the bonding screw or strap installed. Treat that panel just like a service panel. Connect your ground rod(s) too.