Mains sockets and star earth - can anyone explain?

Ground loops

You’ll probably receive a lot of information and advice.

Surely, a neighbouring wall plate will have its earth connected to every other wall plate in the room by parallel wiring between the plates.

I’ll start with this concept first. If you currently have no hum or noise, then you’re lucky.

Your audio system needs to have one common ground that is wired directly to your service panel. These wall receptacles connected together will not have a direct path to ground at the service panel. By plugging your system into this rat’s nest of wiring you are sharing your audio with all the appliances and lighting in your house. This adds noise to the AC line which is audible through your speakers. If these wires have different ground impedances when they meet at the circuit panel, a ground-loop is created. You’ll hear a 60Hz hum thru your speakers if this happens.

lollipopguild12

Surely, a neighbouring wall plate will have its earth connected to every other wall plate in the room by parallel wiring between the plates.

In the US, it's much more likely that the wiring is done in series, and that's the problem. A dedicated line avoids all those extra connections.

What's important to avoid ground loops is keeping all grounds at the same potential. Plugging everything into one outlet is only one way to achieve that.

@lollipopguild 

You might find some interesting reading material here on the subject:

Power Distribution and Grounding for Audio, Video

A star ground is a pattern of 3 or more grounding rods all connected together and connected to the earth ground terminal in a power distribution box. This is usually a more effective ground compared to a single point ground which is common in housing in the US. You should be able to find plenty of information on grounding methods on the net or check out the book "Grounds for Grounding" or find out what the traditional phone companies used in your area.

Unless you have dedicated wiring for your stereo it has short comings, ground loops are just one of the possible issues. Voltage drop is probably a more common issue, wiring is probably to small creating a weak link in the performance.