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Balanced power isolation transformer: grounding
Old 30th May 2019
  #1
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Balanced power isolation transformer: grounding

Hi, can you confirm that the following (Douglas) connection of the central leg of the balanced secondary to the N neutral (and not to the E ground) is correct from the point of view of both safety and line noise cancellation?

I'm interested only on the left side of the pic: just the balanced power transformer used as power line conditioner...

http://www.douglas-self.com/ampins/g...s/gndloop6.gif

Usually all companies connect the central leg to ground E, but this is not safe!

By connecting the central leg to neutral N (and not to ground E), the anti-electrical shock safety switch (RCD) upstream of the whole home plant would trip in case of downstream faults (i.e. a secondary line leg touch the grounded chassis).

If, on the other hand, the central leg was connected to ground E, RCD would never trip.

Since the neutral N is connected to the ground E upstream of the entire civil plant by default , I still should maintain a low-impedance path for all the common-mode noises induced on the secondary, correct ??

I don't see any better (for noise) and safe connection for a balanced power isolation transformer but your comment is highly appreciated.

In order to be sure that my plug has the correct polarity for Neutral, I would put also a 3mA relay between internal N wire and E, so if you reverse the mains plug, the relay will switch (because of the 230V between L and E) and prevent you from power-on the machine.
Old 30th May 2019
  #2
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I'm not up on UK electrical codes, but the diagram you show in your link is the correct and proper way to connect a transformer for "balanced" power. At no point outside the main electrical panel should there be any connection made between the ground (earth) conductors and any current-carrying conductors . . . and the bonding made inside the electrical panel(s) should be done in strict accordance with local electrical codes.

Personally, I have even more skepticism about the practice of "balanced power" than Self . . . in my experience, the components C1 and C2 shown in the diagram are virtually never anywhere near equal . . . and form much more complex reactances than simple capacitors. Especially given the preponderance of switch-mode power-supplies these days, the real leakage equation in a complete studio is a huge can of worms, with intermodulation of various switching frequencies and mains harmonics, the overlay of self-resonances of a whole bunch of transformers, the complex impedance of wiring and internal line filters, etc. etc..

I can take no issue with trying it out and seeing if it's something that you feel improves things in your particular situation . . . but from a theoretical standpoint, it's an absolute random throw of the dice as to whether or not any real improvement will be made.
Old 30th May 2019
  #3
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Radardoug's Avatar
 

Tried it, balanced power is a complete waste of time.
Old 31st May 2019
  #4
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Murky Waters's Avatar
 

My understanding is that neutrals on the secondary of any transformer need to be grounded (earthed) at the transformer. Not via the panel-fed neutral. This does not seem to be the case in your diagram.
Old 1st June 2019
  #5
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Quote:
Originally Posted by Murky Waters View Post
My understanding is that neutrals on the secondary of any transformer need to be grounded (earthed) at the transformer. Not via the panel-fed neutral. This does not seem to be the case in your diagram.
In your case (grounding/earthing secondary) it is not safe. Check my two LTspice simulations.
If you ground the secondary, the Safety Switch or RCD will never trip in case of fault (short circuit over chassis).

https://ggianluca.wixsite.com/opampl...-line-isolator

But I understand there is so much danger confusion over internet and also among manufacturers too. In youtube there are lot of videos in fact that suggest to disconnect ground from isolation transformers' secondary.
Old 1st June 2019
  #6
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Quote:
Originally Posted by Radardoug View Post
Tried it, balanced power is a complete waste of time.
Quote:
Originally Posted by kirkus View Post
I can take no issue with trying it out and seeing if it's something that you feel improves things in your particular situation . . . but from a theoretical standpoint, it's an absolute random throw of the dice as to whether or not any real improvement will be made.
I fully agree with you, Kirkus.

Some screen connections, or iso transformers make the sound worse.
No possible to simulate, only try and listen.

Also any large EMI cap across primary or secondary can change the sound, better or worse.

I tried a lot of configurations: the 80% sounded worse. I posted in my website the only one which is really bringing "imaging" improvements. May be I will change it again. The cap across the primary must be selected on the fly. In my case, with my custom iso transformer, any EMI filter on the secondary sounded worse.

Hence, Radardoug, I suspect you didn't too many configurations and listening tests.

The issue is that any large cap, long mains wiring or inductance in the power path may resonate somewhere and have effect in the audio band. But it is impossible to simulate or measure this. You can only try and listen.

My balanced tranformer have 4 screens and a flux copper band, plus balanced outputs. The capacitance across those and windings is huge due to their size (hundreds of picofarads): I can measure them when are not grounded, but it is impossible to simulate such a complex model and predict the effect on sounds, as Kirkus said.
Old 1st June 2019
  #7
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Murky Waters's Avatar
 

Quote:
Originally Posted by ygg View Post
In your case (grounding/earthing secondary) it is not safe. Check my two LTspice simulations.
If you ground the secondary, the Safety Switch or RCD will never trip in case of fault (short circuit over chassis).

https://ggianluca.wixsite.com/opampl...-line-isolator

But I understand there is so much danger confusion over internet and also among manufacturers too. In youtube there are lot of videos in fact that suggest to disconnect ground from isolation transformers' secondary.
In my country, it's the law.
Old 1st June 2019
  #8
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JohnRoberts's Avatar
 

Quote:
Originally Posted by ygg View Post
Hi, can you confirm that the following (Douglas) connection of the central leg of the balanced secondary to the N neutral (and not to the E ground) is correct from the point of view of both safety and line noise cancellation?

I'm interested only on the left side of the pic: just the balanced power transformer used as power line conditioner...

http://www.douglas-self.com/ampins/g...s/gndloop6.gif

Usually all companies connect the central leg to ground E, but this is not safe!
indeed... one could fill a book with the stories about "ground".

I am not a fan of calling safety ground "E". Earth is usually a separate connection running to a ground rod from Neutral & Safety ground where they are bonded together in only one place inside the electrical panel.
Quote:
By connecting the central leg to neutral N (and not to ground E), the anti-electrical shock safety switch (RCD) upstream of the whole home plant would trip in case of downstream faults (i.e. a secondary line leg touch the grounded chassis).

If, on the other hand, the central leg was connected to ground E, RCD would never trip.
Might and might not but not correct. GFCI trip current in US is 6mA, don't know about RCD threshold for leakage current.
Quote:
Since the neutral N is connected to the ground E upstream of the entire civil plant by default , I still should maintain a low-impedance path for all the common-mode noises induced on the secondary, correct ??
Safety ground is bonded to neutral in the electrical box so should provide adequate low Z path for shield noise.
Quote:

I don't see any better (for noise) and safe connection for a balanced power isolation transformer but your comment is highly appreciated.
That drawing ignores wiring up outlets, so I will too
Quote:
In order to be sure that my plug has the correct polarity for Neutral, I would put also a 3mA relay between internal N wire and E, so if you reverse the mains plug, the relay will switch (because of the 230V between L and E) and prevent you from power-on the machine.
Balanced power is GOP (good on paper) but unclear how much benefit it actually provides with properly designed gear.

JR
Old 1st June 2019
  #9
A large iso power transformer offers galvanic isolation from the power grid and related loads that may pass noise like AC systems. They are expensive and need to be installed by a licensed contractor.
Old 6th June 2019
  #10
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audiospecific's Avatar
 

Quote:
Originally Posted by ygg View Post
If, on the other hand, the central leg was connected to ground E, RCD would never trip.
On the leg spitting transformer (the first transformer), Its typical to either let that float (common in industrial plants), or derive a new neutral leg and Earth (FG in us) connection with a grounding rod and connecting the center tap to the rod and bring out two wires (neutral and ground) and into a new distribution panel. The protection upstream of the leg split transformer is only supposed to trip on faults with the primary. And the new power distribution after the transformer's secondary should have the RCD/gcfi breakers/outlets installed to protect downstream.

If you tie the primary's neutral to the secondary's center tap, it defeats what you trying to accomplish with "balanced" power. It supposed to derive a clean power and neutral legs from a noisy distribution source.

But seriously, an electrician should be doing this. Not you.
Old 6th June 2019
  #11
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My .02cents:
First the word Neutral is used incorrectly by some, BUT we are from two different sides of the planet.
Here is the USA the NEC states the "Neutral" is a point that is balanced between two points (120V 0V 120V for example..If not its NOT a Neutral its a Grounded conductor.. Which a Neutral is ALSO a grounded conductor..

As for "Balanced power" for me it depends VERY much on other variables IF it will/could make a difference in cleaner AC power..
Look at a typical Step down transformer from the Power company, draw it out on paper and see how it looks..
Do you notice something familiar?
Old 6th June 2019
  #12
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Quote:
Originally Posted by nosebleedaudio View Post
My .02cents:
First the word Neutral is used incorrectly by some, BUT we are from two different sides of the planet…... Which a Neutral is ALSO a grounded conductor..
Correct.

I replicated and simulated in LTspice the Douglas trasformer scheme and, trust me, it works safely!
At least in Europe where Neutral and Earth are bonded together before RCD.

The RCD trips in case of faults only if the central tap is connected to neutral and not to earth.

And the output is still balanced vs earth since neutral and earth are bonded together.

Check my website for the simulations. Next measure: common noise rejection, but I need a microvoltmeter which i don't own. I can only measure between 0 and 1 mV in my multimeter, thus about -100dB, but signal is below multimeter sensitivity.
Old 6th June 2019
  #13
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The lower case words 'earth' & 'ground' cause all sorts of confusion and in AC power all sorts of safety issues.
In the US, the NEC (National Safety Code) has a special article (with lot's of rules) for balanced power.
Old 7th June 2019
  #14
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by speedskater View Post
the lower case words 'earth' & 'ground' cause all sorts of confusion and in ac power all sorts of safety issues.
In the us, the nec (national safety code) has a special article (with lot's of rules) for balanced power.
nec 647:
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