Correct PSU Wiring

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I have attached an image of my understanding of a PSU connection. The bit I'm not sure about is the Earth wire. I know it's not strictly needed - but I'd prefer to have it there. These question apply for the UK - but they may be universal?

1) Do I need to attach Neutral to the Earth?

2) Is Ground and Earth the same thing?

3) What is the pinout for a three pin computer/kettle etc. cable (in the UK only?)

4) Are there any problems with the circuit as it stands?!

Thanks - please help me from blowing myself up!



  • psu.jpg
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Grounding can be confusing... There are the safety issues, and then the noise issues.

I'm not an expert, but here is my understanding:

The neutral should NOT be connected to the "Earth". The "Earth" connection is a safety ground - it should be connected to the chassis, and no current should flow through it under normal circumstances. It is there in case the Live wire should somehow contact the chassis. In this case, current will flow through the saftey ground and the fuse or breaker will trip, ensuring that the chassis doesn't become a shock hazard.

The centre tap on the transformer is a floating "common", or zero volt point. This is where your speaker return should connect. Your input return connects here too, though perhaps not physically - maybe it is better to physically connect the input return to the amp pcb? I'm not sure.

Now, as to whether the transformer common should connect to the chassis... Probably not directly. Maybe through a resistor or a rectifier, to eliminate noise.
My opinions to your questions:
1.) No- it's already connected at your service panel.
2.) Yes -Ground (USA) Earth (GB)
3.) N/A
4.) a. Maybe--- depending on your xfmr/design, the two primary windings should be wired in parallel---not in series as you have drawn. (Assuming a standard four winding torid xfmr)
b. The secondary as drawn looks fine to me "if" the ground wires as shown are executed in the "star" method.
Good Luck!
As I mentioned before, the Earth (or Ground) MUST connect to the chassis for safety reasons. The "HQG" point should probably not be directly connected to the chassis for noise reasons - usually it is connected via a resistor or rectifier.

Take a look at the power supply schematic on this page (from

Here you can see what I mean about connecting the common through a rectifier to the chassis.
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