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Discussion of AC mains isolation transformers


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6 minutes ago, austinpop said:

 

I know more than one or 2 CA'ers just like your inspector. 9_9

 

Oh, I know one or two as well. I'll guess we have those incommon! ?

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On 2/1/2018 at 10:41 AM, Jud said:

First, thanks to many people in this thread - John Swenson, Superdad, and especially Speedskater - for assistance and encouragement that allowed me to have a Topaz transformer serving my audio system circuit in my new home.

 

I wanted to post because I thought this tidbit might be interesting: Because the usual electrical inspector for the area had his son's wedding to attend, the chief inspector for the state came out to inspect the electrical installation, including the transformer. While done to the specifications in the (invaluable) Middle Atlantic paper, the installation was sufficiently unfamiliar to the inspector that he required it to be changed so the transformer draws its power from a wall plug rather than the original hard-wired arrangement.

 

Why did you need an electrical inspector?  Is that a law where you're at?  Will he ever be coming back for another look?

 

On 2/1/2018 at 11:03 AM, Superdad said:

Okay, found the plate photo (click for larger image):

5a7347a1ea69d_Topazplate.thumb.jpg.81d50f2ea19a0b71d4b14c05a9684027.jpg

 

And this post by @One and a half is an invaluable resource for anyone that buys a Topaz tranny:

https://www.head-fi.org/threads/topaz-low-capacitance-isolation-transformers-for-affordably-clean-power.857448/page-9#post-13804344

Great instructions on checking/verifying that all is okay.

 

The problem with that diagram is it doesn't explain how to properly connect the ground.  A jumper between the neutral and ground needs to be added on the secondary.

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33 minutes ago, Johnseye said:

 

Why did you need an electrical inspector?  Is that a law where you're at?  Will he ever be coming back for another look?

 

The electrical work on my new home had just been completed, so it had to have final inspection and signoff.  The transformer was part of that electrical work.  No, he won't be coming back.

 

I doubt you'd need an inspection, but if a licensed electrician does the installation, he/she may want to pull permits, depending on the extent of the work.

One never knows, do one? - Fats Waller

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. - Einstein

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1 hour ago, Johnseye said:

The problem with that diagram is it doesn't explain how to properly connect the ground.  A jumper between the neutral and ground needs to be added on the secondary.

 

Same as the manual that comes with your car, it doesn't give you hints on how to drive it, or a manual on Word on how to write prose. Same with the Topaz, it doesn't know what the primary or secondary voltage will be, and where the shields are to be connected, it's up to the owner to decide. 

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Hi guys, @Superdad, @One and a half, @Speedskater @Johnseye and @Jud, apologies if I forgot anyone, HUGE thanks for all the guidance and advice.

 

Sorry I was missing from the thread for a bit, several late nights/early mornings at the hospital for emergencies (I'm a physician) have me beat.

 

@Johnseye you have hit the nail on the head. The diagram does not explain how to attach the ground wires on the input and output side. I'm going to devote a few hours tonight in trying to figure out how things should be connected, but if anyone has a photo (maybe @Superdad or @One and a half, perhaps superdad's USA setup would be more relevant?) that would be hugely appreciated!!

 

The X1-4 and H1-4 parts are pretty self-explanatory, I hope. I plan on following Gary's guide from Headfi on testing, just had a insulation tester delivered today!

 

Thanks so much to all of you, once again.

Yeang

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On 1/10/2018 at 6:11 PM, One and a half said:

Each winding is rated at 120V.

There are 2 x120V windings on the primary and 2 x 120V on the secondary.

 

Normal supply

use an iec class D breaker, don’t know the equal in Nema std.

 

120V input, bridge the two windings together on the primary 

H1 to h3

H2 to H4

Repeat bridging on the secondary 120V output.

X1 to X3

X2 to X4

hot output on x1

neutral output on X4

ground the X4 and the shield together.

Use a standard GFCI on the output.

 

Capacitance is the same regardless of the windings connections.

 

Balanced mode

Connect primary with h2 h3 shorted

connect hot to h1

neuteal to h2

 

secondary

short x2,x3, ground this point and the shield tog

hot 1 x1

hot 2 x2

use a 2 pole GFCI-important it’s a 2pole

 

On 1/13/2018 at 8:28 PM, One and a half said:

Yes, there's a screw stud on the output box on the frame of the Topaz. Wire a green ground wire with an eye type crimplug from the screw, to X4 and connect the black flying wire that comes from within the transformer also to X4. The earth point on the primary runs through to the secondary box.

The ground to the outlet remains on the screw stud , also with an eye crimplug. 

 

44 minutes ago, seatrope said:

Hi guys, @Superdad, @One and a half, @Speedskater @Johnseye and @Jud, apologies if I forgot anyone, HUGE thanks for all the guidance and advice.

 

Sorry I was missing from the thread for a bit, several late nights/early mornings at the hospital for emergencies (I'm a physician) have me beat.

 

@Johnseye you have hit the nail on the head. The diagram does not explain how to attach the ground wires on the input and output side. I'm going to devote a few hours tonight in trying to figure out how things should be connected, but if anyone has a photo (maybe @Superdad or @One and a half, perhaps superdad's USA setup would be more relevant?) that would be hugely appreciated!!

 

The X1-4 and H1-4 parts are pretty self-explanatory, I hope. I plan on following Gary's guide from Headfi on testing, just had a insulation tester delivered today!

 

Thanks so much to all of you, once again.

Yeang

 

The two posts I quoted from One and a half enabled me to connect it properly and get a correct ground indicator from the outlets.

Digital chain: Synology DS1815+ -> Modified Buffalo switch-> SOtM sNH-10G-> Custom Audiolinux server (sCLK-EX modified motherboard, Mutec REF 10)-> EtherRegen-> AL NUC NA (sCLK-EX modified)->  Holo Spring L3 -> Audio Research LS28-> Benchmark AHB2 -> Paradigm Persona 9H, JL Fathom sub

Power: Paul Hynes SR7, Uptone LPS-1.2, sPS-500, Topaz 91001-31 Isolation Transformer

Analog chain: VPI Prime with Ortofon Quintet Black cart -> Simaudio Neo 310LP-> Audio Research LS28-> Benchmark AHB2 -> Paradigm Persona 9H

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12 hours ago, Speedskater said:

Just came across a new 1740 page book in the public library.

"Mc-Graw-Hill's Nation Electrical Code 2017 Handbook"

 

It expands on and discusses the 1000 page NEC code book. But it has a much smaller font. In reading a few sections, I learned a lot.

 

That's why I hang around a website where people who are up for reading 1740 page books are available. :)

One never knows, do one? - Fats Waller

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. - Einstein

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13 hours ago, Speedskater said:

It expands on and discusses the 1000 page NEC code book. But it has a much smaller font. In reading a few sections, I learned a lot.

 

 That was before your eyes went all blurry ? :D

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Question to all you electrically savvy people, including @One and a half @Speedskater @Superdad :

 

I’m getting ready to do live 120V testing of my Topaz, after passing all tests with insulation tester (>1Mohm which is the limit of my cheap tester). 

 

I cut a 18 AWG power cord and was just planning to wire it to the terminals of the topaz (mine are bare terminals only), just to test output voltage, without any load or just minimal load with something expendable after I confirm correct voltage. 

 

I assume that even though the xformer is 5kVa, if there’s no load on it, it’s ok to have a thin 18 gauge power cord on it? Or will it attempt to pull enough current to melt the 18awg power cord?

 

need some reassurance before I blow up anything... 

 

thanks!!

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23 minutes ago, seatrope said:

Question to all you electrically savvy people, including @One and a half @Speedskater @Superdad :

 

I’m getting ready to do live 120V testing of my Topaz, after passing all tests with insulation tester (>1Mohm which is the limit of my cheap tester). 

 

I cut a 18 AWG power cord and was just planning to wire it to the terminals of the topaz (mine are bare terminals only), just to test output voltage, without any load or just minimal load with something expendable after I confirm correct voltage. 

 

I assume that even though the xformer is 5kVa, if there’s no load on it, it’s ok to have a thin 18 gauge power cord on it? Or will it attempt to pull enough current to melt the 18awg power cord?

 

need some reassurance before I blow up anything... 

 

thanks!!

Energising a 2500VA on the bench with no load wasn't a problem with a 16A 230V C type breaker from a wall outlet. 18 guage is pretty thin. Got anything larger like 14g? 

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Thanks much guys, not dead yet. Powered it up with a killawatt on the source outlet. 121V in, 123V out no load, pulls 57 W by the meter (1.8A). Less that I had feared, for a 5kva. 

 

18awg cord cool to the touch, but just ran it for 5 minutes with some hum from the xformer. 

 

 

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On 2/1/2018 at 12:28 AM, One and a half said:

This drawing is the same as in the Middle Atlantic paper, with the transformer connections labelled. Do you need a photo?

 

5a72a4f4bba9e_120Vwiringdiagram.thumb.jpg.773e4a88e07ac434e7078c9aff6e3edf.jpg

 

 

 

 

@One and a half thanks for the great diagram with labels. However, on my unit there is no S1/S2 - maybe that is your way of indicating the shield connection. 

Questions:

1. Is the Faraday shield in continuity with the transformer frame/chassis ground?

2. Any differences in grounding of the secondary, if we do 240V balanced input? I proposed 240V input to my electrician, and he said this "As for tapping the transformer at 240v on the primary and 120v on the secondary, depending on the transformer, we may end up with a floating neutral on the secondary that would have to be bonded to the frame of the transformer.  I don't know if that would be a problem for use."

I had assumed that the secondary neutral was always bonded to the frame, even in a 120V in, 120V out situation. Is that not correct? 

3. Photos of my unit attached below. On the output side, there is a "GND" terminal but not on the input side. Seems that the green wire on the input side is connected to some metal shield, but the green wire on the output side just dives into the depths of the transformer. 

4. Working assumption - green wire on input side wire-nutted to the incoming ground wire going back to main breaker panel. On secondary/output side, jumper X4 and GND terminals. Keep the green wire going into the GND terminal.

Correct?

 

@Superdad @JohnSwenson and @Speedskater @Johnseye any advice would be appreciate too. This is for a 240V input, 120V output, nonbalanced output setup. Quite unsure of the grounding situation here.

 

Thanks so much again!

5a77c1c8970dd_TopazInput.thumb.jpg.c7287f6e124e847495206cec4da2ef89.jpg5a77c1cb7c598_TopazOutput.thumb.jpg.2631247918e919792719157d42a42e55.jpg5a77c23cd1582_Topazoutput2.thumb.jpg.58fdfca5e1269344abb5bd66a72a6836.jpg

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On 1/31/2018 at 10:55 PM, JohnSwenson said:

Here is a picture which I hope brings some light to this discussion. This is 10 years old so there might be some additions to it now, but the basic concepts should still be valid.

 

250-30a105un250-73revise.jpg

 

There are two methods to hook up the output of the transformer, and in both methods the "safety ground" wire of wiring connected to the secondary of the transformer is connected to the center tap of the secondary.  In neither case is there a grounded neutral.

 

In the top one the safety ground wire of the primary (input side) is connected to the safety ground of the secondary wiring. This is the way I have done it for the transformer feeding my listening room.

 

In the bottom one the safety ground of the input is NOT connected to the safety ground secondary side, BUT an additional earth electrode connection is added to the safety ground. The NEC states that this earth electrode should be near the transformer. This earth connection is there to prevent the secondary voltage from wandering all over the place, it is not part of the safety system.

 

If I understand what is meant by a "balanced system" it sure looks like both of these systems are in fact balanced.

 

John S.

Hi John,

 

Thanks so much for your input. Understand the idea of how your setup is grounded, but when you say "safety ground wire of primary connected to safety ground of secondary" above, how is that practically achieved? Do you run a separate ground wire outside of the chassis from the incoming input wire, and connect that to the ground wire of the secondary wiring? Or do you utilize the green wire built in inside the transformer?

 

I was under the impression that the neutral on the output/secondary side had to be bonded to ground, as per @One and a half's diagram. But your post seems to indicate otherwise. 

 

Yeang

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5 hours ago, seatrope said:

@One and a half thanks for the great diagram with labels. However, on my unit there is no S1/S2 - maybe that is your way of indicating the shield connection. 

Questions:

1. Is the Faraday shield in continuity with the transformer frame/chassis ground?

 

The Topaz is a -31 model, so it would have the shield already connected. it would be a mammoth effort to remove the shield connections, if you look closely there's a metal covering over the windings, so this would be the shield. The single earth wire from each side would be connected to it, the primary is just loose. There would need to be another ground connected to the frame of the transformer, and from there to the shield. How is the ground wire fastened to the frame in the primary? Is it tight?

 

5 hours ago, seatrope said:

2. Any differences in grounding of the secondary, if we do 240V balanced input? I proposed 240V input to my electrician, and he said this "As for tapping the transformer at 240v on the primary and 120v on the secondary, depending on the transformer, we may end up with a floating neutral on the secondary that would have to be bonded to the frame of the transformer.  I don't know if that would be a problem for use."

I had assumed that the secondary neutral was always bonded to the frame, even in a 120V in, 120V out situation. Is that not correct? 

 

There's no tappings, this is not an auto transformer. The output is grounded as per drawing on the output. 240V in 120 V as it's connected in the photos now.

 

5 hours ago, seatrope said:

3. Photos of my unit attached below. On the output side, there is a "GND" terminal but not on the input side. Seems that the green wire on the input side is connected to some metal shield, but the green wire on the output side just dives into the depths of the transformer. 

 

This is the shield connection, there needs to be a ground wire to the frame, and don't in US fashion use a construction bolt! It must be a separate bolted connection with the paint removed, the electrician should know how to do this, by drilling into the terminal box. The bolt can be 316 and 316 nuts, washers, spring washers.

 

5 hours ago, seatrope said:

4. Working assumption - green wire on input side wire-nutted to the incoming ground wire going back to main breaker panel. On secondary/output side, jumper X4 and GND terminals. Keep the green wire going into the GND terminal.

Correct?

 

@Superdad @JohnSwenson and @Speedskater @Johnseye any advice would be appreciate too. This is for a 240V input, 120V output, nonbalanced output setup. Quite unsure of the grounding situation here.

 

Thanks so much again!

5a77c1c8970dd_TopazInput.thumb.jpg.c7287f6e124e847495206cec4da2ef89.jpg5a77c1cb7c598_TopazOutput.thumb.jpg.2631247918e919792719157d42a42e55.jpg5a77c23cd1582_Topazoutput2.thumb.jpg.58fdfca5e1269344abb5bd66a72a6836.jpg

4. Yes. Ground the frame first, then the GND terminal, then X4 from the frame.

 

5. The connection terminals are on their last legs having been tightened and loosened many times. I hope they last.

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6 hours ago, seatrope said:

Thanks much guys, not dead yet. Powered it up with a killawatt on the source outlet. 121V in, 123V out no load, pulls 57 W by the meter (1.8A). Less that I had feared, for a 5kva. 

 

18awg cord cool to the touch, but just ran it for 5 minutes with some hum from the xformer. 

 

 

As a rule of thumb, the no load current is roughly the impedance value x full load current. Leave it on for a while, like a few hours but keep coming back to it every 1/2 hour and check the current and the temperature. You're a physician, that should be easy to do. On the case, and no poking metal bits inside!

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@One and a half thank you for your EXTENSIVE input. Much appreciated. 

 

Just to reiterate, so I understand:

1. The shield wires (green) are not in continuity with the chassis.

 

2. I need to make a direct chassis/frame connection by drilling a hole and connecting a wire. - why was this not done from topaz? Were they expecting everyone to do this? Curious. 

 

3. If I have metal armored wire coming into the topaz, with a connection between the armor and the bare metal of the topaz case, the armor should be grounded to the ground wire of the metal armored cable. Do I need to make another hole for the chassis ground?

 

4. If you look at @JohnSwenson diagram and explanation I quoted above, he says that by the diagram, the safety ground of the secondary is connected to the center tap of the xformer. This does not jive in my mind with the scheme you have explained. 

 

Thanks!!

yeang

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16 hours ago, seatrope said:

@One and a half thank you for your EXTENSIVE input. Much appreciated. 

 

Just to reiterate, so I understand:

1. The shield wires (green) are not in continuity with the chassis.

 

2. I need to make a direct chassis/frame connection by drilling a hole and connecting a wire. - why was this not done from topaz? Were they expecting everyone to do this? Curious. 

 

3. If I have metal armored wire coming into the topaz, with a connection between the armor and the bare metal of the topaz case, the armor should be grounded to the ground wire of the metal armored cable. Do I need to make another hole for the chassis ground?

 

4. If you look at @JohnSwenson diagram and explanation I quoted above, he says that by the diagram, the safety ground of the secondary is connected to the center tap of the xformer. This does not jive in my mind with the scheme you have explained. 

 

Thanks!!

yeang

1. Green wires connect the shield physically, they need to be connected to earth ground.

 

2. Rules. To rely on clearing a fault using the armouring of a conduit is folly. EU/AU rules forbid using construction screws or fasteners involved with the assembly or a conduit entry as a means of positive earthing.

Wasnt regulation when Topaz was built.

 

3. Another earth point must be provided. Are you using steel wire armour cable? It provides only mechanical protection for the cable.

use a proper emc cable that has a braid, more than one earth wire and is terminated by a correct emc gland.

do not confuse the shield or armouring of a cable for protective properties for the circuit.

 

4. I’m not entering into a discussion with you on this topic, this is the problem of applying different principles and understanding them compared with a prescribed method such as a picture. The topic of symmetrical differing from earthed neutral distribution can be found in these pages, and guess what, there are more rules to follow for symmetrical power.

 

I will let Speedskater explain or refer the separately derived systems, this isn’t in our rules (yet). One way around this could be restricted earth fault systems, and yes, more rules.

 

earth = ground in the post. Bonding is another topic.

 

 

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  • After some 1300 posts, do we have a real Topaz schematic?
  • The green (or green/yellow) wire is the Safety Ground/Protective Earth conductor. While a shield may be connected to the SG/PE the wire is not a shield.
  • The rules about using an armored cable as a SG are rather complex and limiting.
  • There should be no need to drill holes in the IT frame.
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A question: after reading some earlier posts in this thread I measured the output of my Xentek IT. I was surprised to find out it is wired balanced. I always thought that in a 'normal' setup one of the secondaries was connected to ground so there would be a new hot and neutral. Output voltage between the two poles is (as expected) roughly equal to the input voltage (228V in, 234V out) but I measure approx. 72V between pole 1 and ground and 82V between pole 2 and ground. Is this normal? I would expect to measure approx. 117V on both sides. Anything to do with no load?

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  • Superdad changed the title to Discussion of AC mains isolation transformers

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