>>>> The command station has a 5 amp booster. NCE says to run a ground between the command station and all boosters (connecting to a screw on the bottom of the box). <<<<
>>>> But what should I do with the ground wires coming from the 5 amp power sources needed for the 105 and command station? This is not the 110volt plug wire. From the power source there are 3 wires- two screw into the booster, plus there is a ground. Does this ground need to be attached somewhere? <<<<
No. The third wire you ask about should _NOT_ be connected to any of the NCE boxes. Doing so can cause a ground loop.
>>>> The pb5 with the built in power source has no ground wire, so I guess it just needs a wire connected to the 105 and command station. <<<<
Correct. The ground wire (Also referred to as a “bond wire” or “common” runs between the various NCE boosters. It typically comes into play when an engine moves over the gaps in the rails between booster boundaries. In the case of engines (usually older, such as brass steam – there are others) where the pickup from the right rail is the drivers on the right side of the engine and the pickup from the other rail is via the tender wheels on the left side of the tender, the ground between these particular boosters is used to complete the circuit while the engine is straddling the gap.