Wire gauge from inlet to power transformer

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Headphone amp build, 50va transformer...each channel consumes 150ma, class a.

Is 20awg enough from the ac inlet to the power switch and then to the transformer? If I use a cable with a shield should I attach the shield at the iec ground pin?
 

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The primary wire should be sized according to the fuse or breaker not the load/s.
Shorts do happen and the worst short is one that doesn't blow a safety device in line.
The source of many fires has been found to be use of undersized gauged wire / extension cords.


The safety earth ground must be a dedicated conductor to a chassis bolt using a crimped ring terminal and locking hardware.
I highly recommend IEC inlets with build-in fuses, some even have switches, filters.
 
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Ok, so no go on the 20g shielded from the iec inlet to the switch. Iam trying to use a shielded wire here, as the cable travels all the way to the front of the case to the switch. If one used a shielded wire and attached the shield at one end would where would you attach it? The third pin on the iec inlet?

The inlet is fused (.5a), the psu ground will attach to the chassis via a cl60 thermistor. The chassis will be attached to the ground pin, of course.
 
If one used a shielded wire and attached the shield at one end would where would you attach it? The third pin on the iec inlet?
I would NOT count on a shield, just use twisted pairs and mainly use space / distance from sensitive circuits. it's the magnetic coupling at 60Hz not the electric fields that are problematic.
I'd use regular stranded hookup wire and ~2 to 3 twists per inch and locate wiring in corners of the chassis, you can dress it up with heat shrink.
 
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You should be using mains rated cable.
It is usually double insulated.

Connect the PE Terminal to the Chassis using a Green/Yellow mains rated wire.

Use 2core mains rated cable for the Live and Neutral connections to the fuse and switch (if fitted) and then to isolating transformer.

ALL mains wiring AFTER a fuse, MUST be rated for more than the fuse current rating.

One disadvantage of using 2core double insulated mains rated cable is that the cores are not usuaully twisted. This increases the interference. Twisted pair is better, if you can find any with double insulation. Mains 3core is often built with a slight twist.

An alternative is to use the insulated wires from a mains cable and twist them yourself. Then add on a second layer/s of insulation.
I always use RED insulation tape with 55% overlap as an extra WARNING layer over internal mains wiring.
The 55% overlap ensures at least two layers of tape along the whole cable. I start at one end and wind on the 55% overlap till I reach the other end and then wind all the way back to the beginning with a second set of 55% overlap. That guarantees 4 layers of insulating tape.
 
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