Polarity of the power cord

[stefanovesa]

Hello,
probably a topic already discussed, because I have found some references in other threads, but nothing complete.
Living in Italy, equipment usually ship with Schuko (3 prongs) power plugs or simple 2 prongs power plugs, when no protective earth is used.
The plugs are not polarized, i.e. neutral and live wires can be inverted. No user manual usually gives any hint about a preferred insert of the plugs in the wall sockets.
Anyway, here and there I read suggestions to respect the phase of the connected equipment, so usually, using a phase screwdriver, I try to align L and N marks on the cord at the gear side.
But is it needed? Is there any real benefit for audio gear?
Thanks
Stefano

 

[DVDdoug]

I live in the U.S., but it shouldn't matter.

The "polarity" is important with regular light sockets because you can touch the threaded part when screwing-in a light bulb and that part should be neutral.

With most electronic devices the AC goes in to a transformer which "doesn't care" and the transformer isolates the high and low voltages. Without a separate ground connection there is no actual-physical connection between the electronics and the wall socket at all. (Transformers transfer/convert the power electro-magnetically.)

In the very-old days, some tube equipment didn't have a transformer and the chassis was connected to the neutral. If you plugged it in the wrong way you could get a shock from touching the chassis. Usually, the chassis of a radio or TV was inside an insulated wood or plastic so it was somewhat protected. But guitar amplifiers have a "ground" where the guitar plugs-in and a lot of guitar players got an occasional shock when the power connector was reversed.

 

[Thomas_A]

Regarding this, I’ve never understood whether the claim that orientation may change the way the chassis current behave is correct or a myth.

 

[Speedskater]

It's correct in that there may be a small difference.
Power transformers primarys are wound asymmetrically. So there is more capacitance to the chassis on one terminal than the other. So the terminal with more capacitance will have more leakage current noise than the other.
But it is unsafe to swap the wires in the line cord.
Skilled circuit designers spec how their power transformers are wired.

 

[stefanovesa]

It's correct in that there may be a small difference.
Power transformers primarys are wound asymmetrically. So there is more capacitance to the chassis on one terminal than the other. So the terminal with more capacitance will have more leakage current noise than the other.
But it is unsafe to swap the wires in the line cord.
Skilled circuit designers spec how their power transformers are wired.

No, I do not disassemble the cord. Usually the IEC side of the cord has L and N marks so I simply change the insertion position of the cord at wall socket side until L is the actual L pole.

 

[Speedskater]

No, not you.
But I have read about other audiophiles doing it.

 

[Thomas_A]

Isn’t it a difference between US and EU plugs re possible orientations (those with safety grounds)?

 

[AnalogSteph]

It's correct in that there may be a small difference.
Power transformers primarys are wound asymmetrically. So there is more capacitance to the chassis on one terminal than the other. So the terminal with more capacitance will have more leakage current noise than the other.

So in this case it should be easy to determine which orientation is the better one - plug in the device by itself and measure residual voltage between chassis and protective earth for both variants. Mind you, it should not normally be anything to be concerned about either way, but the bigger the power transformer the more relevant it is likely to be.

Isn’t it a difference between US and EU plugs re possible orientations (those with safety grounds)?

It's actually more complex. The likes of US, UK and Australian plugs are polarized. Europe is a mixed bag of various types, some of which are polarized (e.g. French CEE 7/5) while other prominent ones (e.g. CEE 7/3 a.k.a Schuko) are not.

Mains electricity by country - Wikipedia

en.wikipedia.org

 

[pma]

So in this case it should be easy to determine which orientation is the better one - plug in the device by itself and measure residual voltage between chassis and protective earth for both variants.

Exactly.

 

[Sokel]

I have posted measurements in numerous threads, there are devices that their mains noise is some 20-30dB higher at the "wrong" orientation.

There's also devices where you can measure the ground potential on the metal case as high as 120V the wrong way and as low as 12V the right way (not harmful of course, that would be a crime, current is really low) .

There's also² cases where hum occurs the wrong way and disappears when put right.

 

[stefanovesa]

I have posted measurements in numerous threads, there are devices that their mains noise is some 20-30dB higher at the "wrong" orientation.

There's also devices where you can measure the ground potential on the metal case as high as 120V the wrong way and as low as 12V the right way (not harmful of course, that would be a crime, current is really low) .

There's also² cases where hum occurs the wrong way and disappears when put right.

For an absolute beginner as me, can you explain how to measure it and which tools are needed (multimeter?) Thanks!

 

[Mnyb]

There are some "pens" that finds electrical wires in walls these can also measure the stray field from a transformer , in the past i've used these by measuring how close to the chassi i can move the "pen" before it lights up ?

This might be based on audiophile myths , if someone knows better please inform me . its seem plausible but i don't know for sure ?

 

[Sokel]

For an absolute beginner as me, can you explain how to measure it and which tools are needed (multimeter?) Thanks!

For the residual voltage between chassis and protective earth ,yes, a DMM will do.
Just put one probe on a screw of the chassis or an unpainted spot and the other at the PE.

Try both orientations.
For FFT ones you will need more gear.

 

[Sokel]

A quick and dirty with a prosound el. crossover I have handy and it's a little sensitive to it:



The right way


The wrong way



...and the difference

It's small for the above, other may suffer more or none at all, it's random.

 

[audio_tony]

I have posted measurements in numerous threads, there are devices that their mains noise is some 20-30dB higher at the "wrong" orientation.

There's also devices where you can measure the ground potential on the metal case as high as 120V the wrong way and as low as 12V the right way (not harmful of course, that would be a crime, current is really low) .

There's also² cases where hum occurs the wrong way and disappears when put right.

This can be quite common with switch mode power supplies, often due to there being a small value capacitor connected from the mains side to the secondary side (usually the negative of the DC output).
Swapping the mains polarity results in the capacitor being connected to live, and hence the current flow into the DC part.
It's usually a very low current, but can influence audio measurements if it's powering the device under test.

EDIT: @Sokel I realise you probably know this.

 

[Sokel]

This can be quite common with switch mode power supplies, often due to there being a small value capacitor connected from the mains side to the secondary side (usually the negative of the DC output).
Swapping the mains polarity results in the capacitor being connected to live, and hence the current flow into the DC part.
It's usually a very low current, but can influence audio measurements if it's powering the device under test.

It's not only about SMPS, the above x-over uses a traditional 15-0-15V PSU with toroidal trafo.
It's really random.

 

[pma]

Anyone willing to learn something on this subject should read this:

https://www.jensen-transformers.com/wp-content/uploads/2014/08/generic-seminar.pdf

 

[solderdude]

Hello,
probably a topic already discussed, because I have found some references in other threads, but nothing complete.
Living in Italy, equipment usually ship with Schuko (3 prongs) power plugs or simple 2 prongs power plugs, when no protective earth is used.
The plugs are not polarized, i.e. neutral and live wires can be inverted. No user manual usually gives any hint about a preferred insert of the plugs in the wall sockets.
Anyway, here and there I read suggestions to respect the phase of the connected equipment, so usually, using a phase screwdriver, I try to align L and N marks on the cord at the gear side.
But is it needed? Is there any real benefit for audio gear?
Thanks
Stefano

Yes, it can matter in some cases as has been explained above a few times.
In one 'position' the leakage current can be lower than in the 180 degrees rotated position with some gear.
In the past I have been able to fix some weird ground loop issues with this method.

I did this by plugging in each device not connected to anything.
Then measuring the leakage current from the RCA shield to safety ground and look for the lowest position. With most gear there is little to no difference (depends on the power supply) but in some cases it does.

Usually it does not become audible but in some cases it does and this trick can help, especially with double isolated gear.

 

[Speedskater]

Another Bill Whitlock (Jensen Transformers, retired) seminar paper:

An Overview of Audio System Grounding & Interfacing
9/4/2012

https://jhbrandt.net/assets/resources/An_Overview_of_Audio_SystemGrounding_and_Interfacing.pdf

 

[Thomas_A]

At last - do power cords matter? Yes the can!