Proper LEN > TxF Primary Wiring

[Gtr0]

Hello, Happy New Year!

Looking at schematics from different manufacturers I find conflicting, or at least different, ways of wiring up between power socket and transformer.

The way I have always done it is
L > Fuse > Switch (SPST) > Primary TxF
E > Chassis
N > Voltage Selector > Primary TxF

My switch is a Carling 110-63, so it's a SPST.

I see Fender more or less seems to do it similarly, some other manufacturers put the voltage selection in line with Live and/or use DPDT switches.

Can someone offer the proper low-down on this?? My common sense tells me for the voltage selector that it does not matter which line it is tied to. My common sense also tells me that my common sense is wrong more often than not when it comes to electricity, so I'd rather ask :-)

Thank you.

[d95err]

I would never make a design that is dependent on which connection is Line and which is Neutral. You simply can’t rely on this being correctly wired in whatever you plug into, and at least in Europe, the plug can be inserted either way, so it’ just random.

I would always use a DPDT. I assume that modern electrical regulations require DPDT (just a guess though).

[SoulFetish]

I would always use a DPDT. I assume that modern electrical regulations require DPDT (just a guess though).

They do require DPDT in new designs that don't have a detachable mains cable (like an IEC).

I would never make a design that is dependent on which connection is Line and which is Neutral. You simply can’t rely on this being correctly wired in whatever you plug into, and at least in Europe, the plug can be inserted either way, so it’ just random.

So, it's an interesting point, particularly with respect to European mains plugs.
I'm not sure about mains electric code in Europe, but in North America, the neutral conductor is the designated load/current return conductor. Further, both neutral and earth conductors must be able to carry fault currents and be rated accordingly. For this reason, they (Live and Neutral) are not interchangeable and must maintain their polarity (in our application).
This is the reasoning for why the live conductor is fused, and why the neutral should not be. First, the neutral needs to maintain a closed circuit for fault currents to trip the breaker in case of a fault. If the neutral was fused, the fuse interrupts this function.
The other reason the neutral is not fused is, even though the circuit would be broken, there might still exist a live voltage hazard inside the equipment potentially putting someone at risk of shock. This is why the live connection is fused right at the entrance to the device generally.