Discussion of AC mains isolation transformers

[drjimwillie]

 I have two dedicated 10 gauge, 20 amp lines from my system.  I have my 250 W CJ amp plug directly into one of them.  Everything else is on the other one. 

 I know that John S. has said to plug everything into one IT. 

 There has been discussion, as to whether this is best or not for my type of set up. But, has there been any consensus on whether I should plug everything into one IT or if I should get  to IT's, one for each circuit?

 Are used a kill-a-watt and my total consumption is 355 W. 

I have been pricing ITs and a 750 or 1k VA, that would power the entire system cost 3x more than a 500 VA for the non-amp circuit. 

I use the dedicated circuit for the instantaneous current draw opportunity for the amp. 

I look forward to your experience and advice.   Thank you

[drjimwillie]

 Thank you for your advice. 

1.  I could buy one 750 and I could  plug the whole system into it and see which sounds better. The amp  on the same circuit   Or the camp on the separate circuit without an IT. ( no 750s available now  at a reasonable price )

2.  I could buy one 500 VA and to the same experiment as above.  But I will know that it does not have the same overhead, and I would worry that I'm losing some of the dynamics because I don't have the instantaneous current. ( I saw a 500 for $125).  I would worry that I should buy a 750 so that I could have the suggested overhead. 

3.   I could buy two 500s.   One for each circuit. 

 

 I still wonder if anyone who has two dedicated circuits is using ITs and what they have done. 

 

 Things are always slightly more complicated. I have a small hum or buzz and when I connect a ground wire between the chassis of the amp and preamp the bus gets louder.  This is what I'm trying to fix   

 

 

[drjimwillie]

Please help- I just received a MGE ultra isolation transformer  91097-31T it is 750 VA.  the wiring  looks a lot different than what I have seen on other transformers

 

 I would like to wire it for 120 in and 120 out.   I would like to have the option of somebody could also tell me how to wire it balanced. But that would be the next phase. 

 Currently it is wired 120 and 250 out. 

 Also I would like the secondary floating.

 Here I can see that on the output the ground on top is jumper to X4. 

[drjimwillie]

 Thank you so much for the help

 I paged through the thread and found the black and white diagram above. 

 I rewired it and removed the jumper from  The ground to X4. 

 Now I get 125 between the load and the neutral.  Interestingly  75 from the heart to the ground and 40 from the neutral to the ground ( I don't remember exactly the numbers but they totaled up to 116 )

 I thought by removing the ground Jumper from X4, I was ensuring that I had a floating secondary. I was surprised to get any reading between either the neutral or the hot and the ground. 

 So the amperage potential is not the same when it's balanced? It doesn't put out the same amount of energy overall? 

 My full load is 355 W.  this is a 750 W transformer.  If I wire it balanced is this a problem? 

 You guys are the greatest 

[drjimwillie]

On 11/20/2016 at 2:55 AM, JohnSwenson said:

 

This is a floating secondary, the safety ground does NOT connect to the secondary. The output safety ground is connected to the input safety ground. In addition the metal parts of transformer and the shield are connected to the safety ground.

 

This is the type of connection I was talking about in my post above, the secondary is NOT connected to safety ground. This does not need a GFCI on the output.

 

John S.

Hi @One and a half

 This is what I was asking about when I was speaking of a floating secondary. Is there an issue with it, please. I think I must be confused.   

 Does it have something to do with floating the secondary if it is set up for a balanced output? 

 Also  @JohnSwenson on 11/16/16 says measure  voltage between secondary and safety ground (AC volts)  should be close to zero.  When does that happen??

 

 A secondary question I have ( no pun intended ).  When and if the transformer is wired balanced doesn't put out the same amount of power?   Aren't the VA split between the hot and the neutral so that the overall capacity is the same? 

 

[drjimwillie]

@One and a half in the first  message from this morning :  you say. 

"Jumper X2  to X3 (as shown in the photo) and jumper to G. "

Jumper from what to G? Please

 

[drjimwillie]

Hi @One and a half

 I think it looks good thank you! 

X1 - X4 = 126.2

 X1 – X2 = 62.7 

 X4 – X2 =62.7 

 X1 – G = 62.7 

 X4 - G = 62.8 

 I was worried there for minute, or three ?

 

 Now I am only worried that I can only fit these teeny tiny wires as jumpers.   Everything else in my system is 10 gauge. 

 Is this going to limit the dynamics of the transformer? 

 

 

 

 

[drjimwillie]

 Does this mean that the transformer is wired balanced? 

 

 It is interesting that it is completely different then the diagrams above.

 

 If I look at the diagram it is as if I am wiring at 220 and 220 out. 

 

 

[drjimwillie]

On 5/13/2018 at 5:40 PM, drjimwillie said:

Hi @One and a half

 I think it looks good thank you! 

X1 - X4 = 126.2

 X1 – X2 = 62.7 

 X4 – X2 =62.7 

 X1 – G = 62.7 

 X4 - G = 62.8 

 

 If I remove the jumper from X3 - G, does that float the secondary?  I get:

X1 – X2 = 62.7 V

 X4 – X2 =62.7V

 X1 – G = 32V

 X4 - G = 86V

I am assuming that  because I have voltage on the hot and neutral that this is balanced?   If I put a GFI on the outlet,  can I use it like this?

 

 

 

[drjimwillie]

I just received a MGE ultra isolation transformer  91097-31T it is 750 V.  I am in the USA and need 120 in - 120 out.

I have it wired: Primary (input)

120V Hot (black) ->H1

jumper H2 + H3

120V Neutral (white) -> H4

Ground from the wall ->G

 

Secondary (output)

Output 1 Hot (black)

jumper X2 + X3 & X3 + G

Output 2 Hot (white) ->X4

G-> output grounds

 

When I take measurements I get:

X1 - X4 = 126.2

 X1 – X2 = 62.7 

 X4 – X2 =62.7 

 X1 – G = 62.7 

 X4 - G = 62.8 

 

I was told that X1 – X2 has to equal X4 – X2 - Which it does.

 

 If I remove the jumper from X3 - G, does that float the secondary?  I get:

X1 – X2 = 62.7 V

 X4 – X2 =62.7V

 X1 – G = 32V

 X4 - G = 86V

 

X1 – X2 is still equal to X4 – X2, but the two out puts X1 & X4 to ground are not equal.  Is that a problem?

 

I am assuming that  because I have voltage on the hot and neutral that this is balanced?  

I bought a 20 amp GFI outlet,  can I use it like this?

 

I want a floating secondary, I would like it balanced.

J.S. said that a GFI was not required, but I guess that is if the transformer is unbalanced? If it is balanced then I need a GFI?

 

I was told that the center tap and the shields and the chassis have all be wired together.  Aren't all of these Topaz clones wired like that?  I don't have to take this thing apart, do I??

 

I was asking questions at @Cornans experimental tweak thread, but I felt like too big of a disruption.

Thank you

 

 

 

[drjimwillie]

 If the center tap of the two coils on the secondary are required to be grounded for the transformer to be wired balanced, then by definition it is impossible to have a secondary floating?    Is that correct? 

 

 I have read this thread from the beginning, and honestly I'm a little bit confused.  Obviously you have strong convictions that the secondary should not be floating.   J.S. Said that a floating secondary is the normal way the transformer is wired. Will you please elaborate on your perspective?

 

J.S. also said that a GFI is not required.  I am going to get a two pole GFI to use with my project.   Is this only required when the transformer is wired balanced?

 

 I know  we operate out on the fringes, to try to get the best out of our systems.   Sometimes even with the best effort it is difficult to weave it all together to have a complete understanding.  

 I am grateful for your help. Thank you 

[drjimwillie]

On 11/20/2016 at 2:55 AM, JohnSwenson said:

 

This is a floating secondary, the safety ground does NOT connect to the secondary. The output safety ground is connected to the input safety ground. In addition the metal parts of transformer and the shield are connected to the safety ground.

 

This is the type of connection I was talking about in my post above, the secondary is NOT connected to safety ground. This does not need a GFCI on the output.

 

John S.

This is the post I was referring to. I am sorry I called it normal. 

 

On 11/16/2016 at 5:04 PM, Superdad said:

Thanks for your post John.

 

Indeed a true isolation transformer is quite safe. In fact, before there were GFCIs, hotels used to have "shaver-only" outlets which contained--you guessed it, a small isolation transformer.

 

But it turns out that many (likely most) of the in-a-case with outlets units presently sold as "isolation transformers" in fact are not. Due to NEC (and probably EU) requirements--along with a desire for even greater common-mode noise attenuation--they are most all bonding one leg of the secondary to ground. This of course defeats the safety aspects of a "floating secondary" as John describes above.

 

Again, I am not talking about just running the input ground to the chassis and through to the third pin of the output outlets. I am saying that the TrippLites, the Eatons, and many others are connecting one side of the secondary to ground! That is why there are lots of videos by techs and old radio repair guys showing people how to "re-float" their TrippLite "isolation" trans units--since that is important for safety for those folks.

 

Of course the old stock industrial Topaz units are not doing this (though if I bought one prewired with cord and outlets I would check it).

 

And perhaps the "grounded neutral secondary" pseudo isolation units offered to the public these days would indeed benefit from a GFCI.

 

Here is a page from the current Eaton "Power Suppress" series (you can see the secondary being grounded), and all the TrippLite "Isolator Series" pages state "Secondary Neutral Bonding."

 

In the post two above Alex's post refers to "true isolated transformer " the secondary is not connected to ground. These are why I thought "floating" is "normal"

 

So there are different degrees of  floating?

1.  Input ground is connected to the chassis the shield in the output ground. This is what is  in the two posts above, correct? This is safe?

 

2.  If the output ground is not connected,  then a two pole GFI I is required ?

[drjimwillie]

1.   I find this terminal block very hard to work with. I ordered another terminal block, I hope it fits.  If you look at the terminal wire hole, you will notice that the terminal screw pushes down a tab, that stays halfway across the hall and makes it very hard to put wire in. 

 My plan is to put a crimp ring or spade terminals on the existing wires from the transformer.  The wires are so short that I am afraid I will not be able to get my hydraulic crimper on them.  Do you think I can squeeze my lineman  pliers tight enough to make a sound electrical connection?   I made up a power strip with some nice Hubble industrial receptacles and some Canare 4S11  Star quad cable.  Each of the conductors is 14 gauge together they are supposed to be 11 gauge.  This is a hardwire transformer and I don't think I can fit these two wires in that terminal block.   

2.   It was suggested that I run a new ground wire from the input side to the output side.  I have confirmed that there is no wire running through the chassis. The only ground is made with the chassis ground.   If you look in the cavity of the chassis, it does not look like there is much room to sneak a wire past the coil.  Also, isn't the screen blocking the way in the middle  of the chassis, between the two coils?    I was wondering what the two gray wires were on the output side I thought that maybe they ran in to the shields. But as you can see they do not because  they are connected to what looks like a capacitor. 

3.   It was suggested that all of my grounds tied together in a star ground configuration.    Can anyone help me figure out how to engineer that? Or is the whole idea out the window because there are no leads that connect to the shields or the  Faraday screen. 

 Please, I am looking for whatever wisdom and experience you can contribute. 

 

[drjimwillie]

@AbtrI am planning to wire the transformer  balanced, non-floating. 

( The funny thing is, this is how @one and a half suggested I wire the transformer in the first place. But at least now I understand what I'm doing.)

 In the USA we do not typically use a central GFI.  In this instance, if I do not wire a GFI after the IT, is it in issue?  A short would still blow the breaker, correct? 

 Sincerely – thank you for all your help. 

[drjimwillie]

@AbtrThank you. 

 I don't think I'll try purposely shorting it out. That sounds scary. I would have to take some serious safety precautions. 

 Do you think I will be able to run a ground wire from the input side to the output side so I don't only have to rely on the chassis ground? 

 Also it is recommended that I try to bring all the grounds to the same point,  as a star ground.  I cannot visualize how to engineer that and keep all the wires on the interior of the transformer. 

 Do you think I will be successful and trying to change out the terminal block? The wires to the existing one seem very short.   I don't think I can get my hydraulic crimper onto them.   But I was thinking I could use my lineman's pliers, and squeeze them with a good wood clamp that I have to crimp a ring terminal for the new terminal block. 

 

[drjimwillie]

I have two issues with the screw connectors. Although I may have solved one.

1.  If you look at the picture, there is that metal tab that hangs down across the hole for the wire.   It made it very difficult to insert a wire.  This is why you can see  that  the previous owner used these teeny aluminum wires as jumpers.  I have to believe that a teeny wire would impede the electron flow and mess with the dynamics.  I tried to insert a 14 gage jumper, and you can see that I bent the heck out of it trying to get it in the hole.  Now that I have pulled out the terminal block I should be able to  persuade a wire to fit. 

2.   I made up cables which use a star quad with (2) 14 gauge stranded conductors.  The only way that I think I could get that to fit in the hole would be to solder both conductors solid, and then offset them, and solder them together so that only the end of one conductor goes into the connector.    I don't know if that's a good idea ( electrically ) and I'm not good at soldering.   What do you think?

 

 Also, what do you think that thing is that looks like a capacitor on the output?

[drjimwillie]

IOk. Now that I have  pulled the existing terminal block out I can probably fit a 12 gauge wire in as a jumper.  I am I correct in thinking that that teeny aluminum wire as a jumper was an issue?  You can see it if you page up to some of my original photos.

 

 Now my issue is how to work with the star quad cable that has (2) 14 gauge conductors.  What do you think of my idea to offset the two conductors and solder them together so that all I have to do is put the tip of one under the screw terminal?

 

 The capacitor is wired like a jumper from X1 to X4.  I will remove it.   The capacitor is tucked in behind the plate that holds the terminal block.  I only found it because I pulled terminal block off so I could see what was keeping the wires from going in the holes.  This is an MGE Ultra isolation transformer 91097-31T  750VA, so probably built by Topaz. 

[drjimwillie]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1. For 120V -> 120V balanced non-floating output, jump H2 and H3 (and remove the jumpers between H1A and H3 and between H2 and H4), jump X2 and X3 and remove the jumper at the top between G and X4 at the output, connect both the green-yellow wire and the solid green wire to G at the output and jump G to X2/X3 (which is now the secondary center tap). This is safe because your gear's chassis is connected to mains earth and a short to chassis will trip your central GFCI and/or blow a mains fuse.

2.  Now, for 120V -> 120V balanced *floating* output, connect everything as was described above for a 120V -> 120V balanced non-floating output, and simply disconnect the yellow-green earth wire from G at the output but keep the solid green wire connected to G. This is *unsafe* because your gear's chassis is not connected to mains earth and a short to chassis will therefore not trip your central GFCI or blow a mains fuse! However, you can make this safe by installing a 2 pole RCD/GFCI at the output of the IT. Your gear’s chassis is connected to the zero voltage center tap (X2/X3) of the balanced secondary and a short to chassis will trip the 2 pole GFCI at the output of the IT.

 

Hi @Abtr - the first two images are original, before I touched anything.  The last is with the output opened.  We have established that the two grey wires go to capacitor attached to the back of the panel, that I am going to remove.  At the input a green wire goes into the interior and a green & yellow wire attach to the chassis.  At the output I do not have the green wire coming from the interior, only the green & yellow to the chassis. 

 

How can I wire as suggested above if there is no green wire from the interior??

 

when I wired with the jumper X2 + X3 + G, I measure: (#1 above)

X1 - X2 = 62.7V

X4 - X2 = 62.7V

X1 - X4 = 126V

X1 - G   = 62.7V

X4 - G   = 62.7V

 

With the jumper from X2 + X3, but the jumper removed from X3 + G, I measure:

X1 - X2 = 62.7V

X4 - X2 = 62.7V

X1 - X4 = 126V

X1 - G   = 32.3V

X4 - G   = 86.0V

 

All of my receptacles are Hubbell 5362i industrial grade.  To safely try #2 above, floating the ground, I purchased a  Hubbell 5362i 2 pole GFI ( I do not want any weak links in the power chain), it was expensive.  What do I do if I only have the chassis ground at the output?  I will have to look at the terminal block to see what the chassis ground is connected to.

 

I have all of my parts and I plan to wire it up tonight.  I got some of those Wago connectors.   I will let you know how it goes.

Thank you

 

 

 

[drjimwillie]

Thank you so much

[drjimwillie]

On 4/7/2018 at 5:14 AM, Cornan said:

 

Personally I am using a custom made balanced IT from ATL Hi-Fi. Here is the schematics.

 

This IT have a toggle switch to ground or float the secondary balanced center tap that I added to make it possible to quickly compare the two.

 

Hi @Abtr  because my IT only has a chassis ground,  I am having trouble seeing how if I attempt to float the ground by removing the green yellow wire from either the chassis or  The terminal block, how I am able to  maintain some type of ground?  I have included Cornan's  schematic as a reference  of a balanced transformer. My understanding is that, to float the secondary, you are lifting the ground from the secondary , it is the coil that floats, but you still maintain a direct ground from input to output. It just bypasses the secondary coil. 

 I have the jumper from the outgoing safety ground to the center tap, if I disconnect the yellow green wire from the chassis am I still making a connection to ground through the center tap?  I don't see how this happens because it is only an induced connection between the input in the output coil's. It appears to me that if I  disconnect the green yellow wire I am lifting all ground.  I have the jumper X3 + X2 + G but if a disconnect the green yellow from either the terminal or the chassis then there  is no direct connection to the input ground. 

Do I have to make a new connection  input to output ground with out using the chassis???  

 

 I have included a picture of my newly wired output. And you can see that I  used the existing screw down terminal blocks. To solve the issue with the (2) 14 gauge wires from my star quad AC cable, I used a Wego connector, which allowed me to bring two wires in and then one 10 gauge wire out. I was  only able to use 14 gauge for my jumpers, because I have to fit two of them into one screw terminal. Also, unfortunately I was only able to use a 14 gauge  for the ground because I have a jumper in that screw terminal,  otherwise I have a 10 gauge for ground everywhere else.   

[drjimwillie]

I think this is how my IT is wired now. 

 

[drjimwillie]

4 hours ago, Abtr said:

 

Yes, that would be a balanced non-floating configuration.

 On this schematic what would I be disconnecting to float the secondary, please. 

 

4 hours ago, Abtr said:

Don't remove any green-yellow wire from the IT chassis anywhere! In order to 'float' the secondary, just remove the green-yellow wire from connection G at the output terminal block and leave the output equipment ground (the solid green AC output wire) connected to the center tap (via connection G).

The yellow green wire is connected from the terminal block to the chassis. So in practice, whether I disconnect that wire from the terminal block, or from the chassis, the  effect is the same. 

So,  I leave the yellow green connected to the chassis, disconnected from the terminal block, and tape it off. 

 The output/equipment ground, is still connected through the jumper to the center tap. 

 

[drjimwillie]

11 hours ago, diecaster said:

I wouldn't do that......

 Please elaborate.

 If I do float the secondary, I have a nice 2 pole, industrial GFI to put on the output of the IT. 

 

6 hours ago, Abtr said:

Did you try the *non-floating* configuration and did you measure the output?  

 I measured the non-floating configuration when I first received the IT and rewired it, temporarily. I measured 62.7V from X1 - G and with X4 - G; 126V X1 - X4. ( this was with the original input and output cable. )

 Do I have to worry that 126V is too high a voltage?

 Should I consider a voltage regulator? 

I have read Cornan  discussing them but I'm not sure what would be a good choice to use with my 750VA IT and be appropriate for the USA. 

 I am still  wiring the IT. It is slow going, as I can only put in little amounts at a time. I completely rewired my  Power strip with the star quad cable, I added a 10 gauge ground. I ordered crimp closed Connectors,  to replace the wire nuts. They were supposed to be able to accept 6 gage wire, which is what I calculated (7) 14 gauge wires would equal, but there was no way they were going to fit in that connector.  I ended up re-working the wire nuts.

 I will measure everything again before I put it into service. 

 I have a shelf near the ceiling in my basement which is just below and off to the side of my equipment rack, so I drilled a big hole in the floor and I'm going to run my power up from there. This should keep any magnetic fields  away from my equipment. I am even considering putting some aluminum foil on the underside of the floor for shielding,  but I'm not sure if that's necessary? 

 Fun fun fun and I am getting excited. 

 

[drjimwillie]

4 hours ago, Speedskater said:

Are all the first 'ground symbols' part of the green wire Safety Ground that connects to the Neutral in the main breaker box?

Where do the green/yellow 'ground symbols' connect and to what?

 The first safety ground is the ground that connects to the panel which is also bonded to neutral. 

 The second is the connection from the terminal block to the chassis ground  and to the shield. 

 The first  ground shown on the secondary side is the yellow green wire that goes from the terminal block to the chassis ground. And from the terminal block to the center tap.  And from the terminal block to the center tap. 

 The last ground on the secondary side is the equipment ground third prong. 

 The only connection from the primary side to the secondary side for the ground is through the chassis. 

 I annotated my schematic. 

 

 

[drjimwillie]

 I got it hooked up and I plugged it in:

( removed  The capacitor )

 Balanced:

X1-X3. 62.0v

X4-X3. 62.0v

X1-X4. 124.7

 

 Balanced  floating– with the green yellow wire removed from the chassis. 

X1-X3. 61.7

X4-X3. 61.6

X1-X4. 124.7

 

 Tomorrow I'll put it into the system   

 I run it non floating for a while till everything burns in

 

 The Hubble 5362 I 

 It is the receptacle that I use everywhere else in my system. It was  suggested by Richard from Shunyata. I'm hoping that the industrial designation is only because it's beefy.  I will  get the specification and post it.  It looks like a typical kitchen GFI