Isolation Transformers


I bought an isolation transformer from a fellow selling his home audio gear about a year or so ago. It’s a 12” cube that weighs roughly 60 lbs and has 8 plugs in the back. It was apparently used in a hospital. 
I have most of my gear including a tube preamp plugged into it mostly for protection purposes. It puts out a constant 124v which is a few more than what I get directly from the wall socket.
Anyone else using this sort of device as a “power conditioner” and what are the pros and cons of using one? I’m guessing delivering a constant voltage (almost) regardless of the load is the main advantage of this type of device but am wondering if it impedes full current delivery at high amplifier loads. Thanks. 
Dfc79476 b7e2 448b 8f7b 3aed2a5e9ad4kalali
Hi Kalali,

I'm not sure what you have. Can you post the make and model?

An isolation transformer by itself does not regulate voltage. It does eliminate DC and prevent certain types of shock, as well reduce noise due to the inductance. 

A voltage regulator may also be present, but these can be with or without the isolation component. The benefit here is, of course, a tightly regulated AC voltage, though not necessarily surge protection, and it may take a little for the regulator to adjust to incoming and outgoing conditions. 

Best,


E
Isolation transformers have many uses. Google is your friend, punch in what model you ended up with and it's specs. Start with the link below for an explanation to the basics:
http://www.shure.com/americas/support/find-an-answer/transformers-when-to-use-and-how-does-it-work
It was apparently used in a hospital.
What is the Kva rating? It will say on the data plate.

Does it say ’Medical Grade’ anywhere on it?

If yes:
Most medical grade isolation transformer I have ran across float the secondary winding above ground. That means both AC Line contacts on the receptacle outlets are fed from Hot ungrounded legs, conductors. Neither of the two hot conductors have a reference to ground. Therein, not to the metal case/enclosure of the transformer or to the ground contact of the receptacle outlets.

I would suggest you use a volt meter and measure for voltage from both contacts to the equipment ground contact on the outlets.


If the isolation transformer is wired as a Grounded Power System:
Short slot of the outlet to equipment ground should measure 120VAC nominal. (You said it runs 124Vac.)Longer slot of the two, or ’T’ slot, the neutral contact should measure a solid zero volts to ground.

If the isolation transformer was left ungrounded then you have an Isolated Power System. Any voltage readings from either contact to ground will be phantom voltage. Usually a digital meter reading will be all over the place and will not hold steady.

Medical grade transformers are meant to be used by qualified personnel only.
If your transformer floats the secondary above ground you should have an electrician wire it as a grounded power system. It’s simple do.

.
When did they start printing ’hospital grade’ on anything that was? dang, has it really changed that much since I was in the field? OP did say older isolation transformer?

I guess things have: Hospital grade receptacles include the same markings that appear on general use receptacles, and also include “Hospital Grade” or “Hosp. Grade”, typically on the back of the receptacle where visible during installation

Wasn’t always so. I guess code revisions took a big friggin change to assure no mistake. Guess they factored in no one pays attention to the spec sheets any longer. ..hmph
Reminds me of those on the job concentrating solely on their electrical prints and were clueless to look at the architectural and others...*laffs
In Australia 230v to 230v isolation transformers I have use them on my source gear since the 80’s. they provide "Galvanic Isolation" from the mains and block/filter any dc on the mains.

For the US
http://www.surplussales.com/item/_tp/91092-12.html
https://www.bkprecision.com/products/power-supplies/1604A-single-output-isolation-transformer.html

Cheers George
oicu812

41 posts
04-10-2019 6:34pm

When did they start printing ’hospital grade’ on anything that was? dang, has it really changed that much since I was in the field? OP did say older isolation transformer?

@ oicu812

Medical grade.
Example of:   
https://www.tripplite.com/isolator-series-120v-1000w-ul60601-1-medical-grade-isolation-transformer-4....

As others have said, isolation transformers don't regulate, and they don't even really isolate, except in the sense of from DC. It helps to understand how they work in the first place. That alone will answer a lot of questions. Do a search.

Sounds like the one you're using is pretty close to 1:1. Getting a few volts more out than in tells you the windings aren't equal, its not a perfect 1:1 but again, read up and learn how they work.

The one I use is audiophile grade 2:1 step down, the supposed advantage being you can run 240v to the transformer and get 120v out the other end. Which is what I do, and it is better than the exact same wire and connections that were running 120v before.

Of course if you listen to half the guys around here I am long since dead and buried, along with the half the neighborhood I burned down, voiding warranties, experimenting with lethal blah blah blah yada yada.

As if any of this matters. Because it don't. What matters, the only pro's and con's as you put it, is what you heard. If you didn't hear any improvement then sorry, waste of money. If you did, well then you can tell by how much it was worth it. Them's the pro's. All the rest is a con.
I have used isolation transformers in a variety of settings. One, an old 240/120 step down made by Richard Gray for a big home theatre system- the system itself is long gone- was the only thing that would fully isolate a nasty electrical snap from the air compressor motor that energizes one of my tone arms. I now have a better electrical set up and a dedicated line wired to the regular house main electrical system set up for 20 amps for the air compressor. I use one of those Tripplite 1800 watt jobs. In speaking with the tech at Tripplite before I bought it, the secondary is bonded, it is not really floating. There’s at least one reference to this that I saw on the web, so I am not sure their claim of ’medical grade’ is fully accurate, at least insofar as a floating ground on the secondary.
Even though that dedicated line is separate from the sub-system I use for my audio, I added the iso-transformer just to be sure I didn’t get any noise from the compressor motor-- 1/2 HP, pumps about 130 psi (I use around 65 psi for the arm).
My main system has a 10kVA isolation transformer made by Controlled Power in Michigan, installed in a weather proof case- it weighs about 400 lbs, and has surge protection and some EMI shielding. I listened to the system through ’dirty’ power with the new dedicated wiring while awaiting the arrival of this transformer (they are built to order). Frankly, the ’dirty power’ here is way less noisy than my power in New York. Not surprising, but in NY, I was up along the Hudson in a very small village, no industrial stuff. Here, I am in the middle of Austin, several multi-unit apartment buildings nearby and lots of commercial stuff 3 blocks away. Maybe unnecessary, but the system, which uses very high efficiency horns (104db) will reveal all kinds of nasties. System is dead quiet and the transformer does give me a little peace of mind. (It is grounded back to the main household ground which is an Ufer type ground set up).
The Controlled Power is an old school EI- throws off all kinds of nasties, but since it is outside, I don’t care. The small ones, that use toroidals, can hum and buzz and you don’t want them near your listening environment, although I think they throw off less electrical junk. See http://www.soundstagenetwork.com/maxdb/maxdb071998.htm
That said, there are good toroidal types. Torus is very well regarded. I had a big Equi-Tech wall cabinet that I never put into use; those were the cat’s meow at one point and I believe the transformers came from Torus, who does sell them naked, or through a brand that is plug and play with a case and outlets, ready to go.
A good tool in the arsenal in my estimation, but not a cure-all for all ills.
whart

2,018 posts
04-10-2019 9:42pm

I have used isolation transformers in a variety of settings. One, an old 240/120 step down made by Richard Gray for a big home theatre system- the system itself is long gone- was the only thing that would fully isolate a nasty electrical snap from the air compressor motor that energizes one of my tone arms. I now have a better electrical set up and a dedicated line wired to the regular house main electrical system set up for 20 amps for the air compressor. I use one of those Tripplite 1800 watt jobs. In speaking with the tech at Tripplite before I bought it, the secondary is bonded, it is not really floating. There’s at least one reference to this that I saw on the web, so I am not sure their claim of ’medical grade’ is fully accurate, at least insofar as a floating ground on the secondary.
Hi Bill,

The Richard Gray PDU (Power Distribution Unit) is wired as a "Grounded Power System". The neutral leg, lead, of the secondary winding is intentionally bonded to ground, as well to the metal enclosure of the unit. All equipment grounding conductors from the power outlets connect to this common point. Star grounding.

It also sounds like the secondary winding of the Tripplite 1800 isolation transformer is also wired as a Grounded Power System.

Your 10Kva isolation power transformer secondary winding is also wired as a Grounded Power System.



Below are two isolation transformers.

The first one floats the secondary winding above ground. Neither ungrounded conductor has any reference to ground. It doesn’t have any reference to the equipment ground contact on the receptacle outlet either.
The second example bonds one of the secondary legs to ground making it the grounded conductor, the neutral conductor.

Isolated Power System
  • Offers line isolation and continuous noise filtering
  • Internal low-impedance isolation transformer with Faraday shield offers 100% isolation from the input AC line
  • Full UL 60601-1 medical-grade listing with hospital-grade plug and outlet receptacles for the protection of sensitive electronic equipment in patient-care areas
  • Reduces cumulative leakage current of the Isolator and connected equipment to levels less than 100 μA

  • Floating AC output prevents noise coupling from noisy hospital ground circuits and meets agency requirements
  • https://www.tripplite.com/isolator-series-120v-1000w-ul60601-1-medical-grade-isolation-transformer-4...




    Grounded Power System
  • Tripp Lite Isolator series isolation transformer-based power conditioners offer complete line isolation, continuous noise filtering and enhanced common mode surge suppression
  • Supports combined loads up to 1000 watts continuous/8.3A at 120V
  • Isolation transformer with Faraday Shield offers 100% isolation from the input AC line

  • Neutral to ground bonding at the secondary eliminates common mode noise and provides an isolated ground reference for sensitive equipment

  • https://www.tripplite.com/isolator-series-120v-1000w-isolation-transformer-based-power-conditioner-4...

    Jim

    .

    Hey, Jim. I don’t disagree with anything you said, and you know a whole lot more about this than me, but the Tripplites that are hospital grade, such as the one I bought, the 1800HG claim hospital grade receptacles and talk about a floating ground (actually, ’floating AC output’) if you go to the Tripplite website. See
    https://www.tripplite.com/isolator-series-120v-1800w-ul60601-1-medical-grade-isolation-transformer-6...
    Yet the data sheet says: "

    "Secondary neutral to ground bonding eliminates common mode noise, providing an isolated ground reference for sensitive equipment and an inexpensive alternative to the installation of dedicated circuits and site electrical upgrades." https://datasheet.octopart.com/IS1800HG-Tripp-Lite-datasheet-86786.pdf

    Here’s the most current one being used for sale of the unit, says the same thing: https://datasheet.octopart.com/IS1800HG-Tripp-Lite-datasheet-8508521.pdf

    (FWIW, the power switch/breaker on current production is not the green illuminated style but the black more enclosed breaker).

    These are the same units being referred to as far as I can tell, based on model number. And that was borne out by my call with Tripplite tech before I bought the unit. In other words, the claims that the unit has a floating output (interchangeable terminology with ground?) are not borne out by the data sheet or my conversation with the manufacturer and the unit fits into what you described as a grounded system . Am I missing something obvious here? (Not being snarky)



    Thanks for all the responses. Its technically a medical grade isolation line conditioner, an older version of this unit from TSi Power. They seem to use the term isolation transformer interchangeably.
    http://www.tsipower.com/products/isolation-line-conditioners/indoor-isolation-line-conditioners

    Looks like they only sell commercially.
    I would think your isolation transformer would clean some of the grunge from the AC which would in return give you a darker background allowing you to hear more details within the music and perhaps deeper bass, provided you don’t overtax its rating. That’s what I experienced with my Xentek Extream Isolation Transformer (5 Kva) and weighed at least 100 pounds maybe more.
    but the Tripplites that are hospital grade, such as the one I bought, the 1800HG claim hospital grade receptacles and talk about a floating ground (actually, ’floating AC output’) if you go to the Tripplite website. See
    https://www.tripplite.com/isolator-series-120v-1800w-ul60601-1-medical-grade-isolation-transformer-6...

    Bill, (whart),
    An "Isolated Power System" does not float the ground. The output of the secondary winding floats above, (not electrically connected), the ground.

    In the case of a plug and play "Isolated Power System" wired isolation transformer the wall outlet equipment ground is used for grounding of the metal enclosure of the transformer and is also connected to the equipment ground contact on the power output receptacle outlets. The floating output of the secondary winding does not have any reference whats so ever to the AC mains power equipment ground.


    (Note: Same holds true for a hard wired Isolated Power System. Difference is with an Approved hard wired Isolated Power System the system is required by NEC code to have a monitor device that warns the trained qualified personnel when/if a ungrounded conductor of the system faults to ground. Trust me this feature is a must!)




    From the link you provided.
    https://www.tripplite.com/isolator-series-120v-1800w-ul60601-1-medical-grade-isolation-transformer-6....
  • Complete line isolation and noise filtering
  • Hospital-grade plug and receptacles
  • Lowers cumulative leakage current of connected equipment to under 100μA

  • Floating AC output prevents noise coupling

  • Features
    • Offers line isolation and continuous noise filtering
    • Internal low-impedance isolation transformer with Faraday shield offers 100% isolation from the input AC line
    • Full UL 60601-1 medical-grade listing with hospital-grade plug and outlet receptacles for the protection of sensitive electronic equipment in patient-care areas
    • Reduces cumulative leakage current of the Isolator and connected equipment to levels less than 100 μA

    • Floating AC output prevents noise coupling from noisy hospital ground circuits and meets agency requirements

    Whart said:

    Here’s the most current one being used for sale of the unit, says the same thing: https://datasheet.octopart.com/IS1800HG-Tripp-Lite-datasheet-8508521.pdf

    The unit is wired as a Grounded Power System.
    From the Link:
    "Secondary neutral-to-ground bonding virtually eliminates common mode noise, providing an isolated neutral-groundreference for sensitive equipment, and an inexpensive alternative to dedicated circuits and site electrical upgrades."

    .

    https://datasheet.octopart.com/IS1800HG-Tripp-Lite-datasheet-86786.pdf
    "Secondary neutral to ground bonding eliminates common mode noise, providing an isolated ground reference for sensitive equipment and an inexpensive alternative to the installation of dedicated circuits and site electrical upgrades.

    To me that says in the field (site) the Isolated Power Power System can easily be wired as a Grounded Power System. Which is true. A bonding jumper is installed from the secondary neutral conductor to the metal enclosure of the transformer.

    Bill, probably the easiest way to find out if the unit is wired as an "Isolated Power System" or a "Grounded Power System" is with a plug in AC circuit/polarity tester.
    https://www.homedepot.com/p/Power-Gear-3-Wire-Receptacle-Tester-50542/206212329?cm_mmc=Shopping%7CG%...

    If the unit is wired as an Isolated Power System the tester will indicate an "OPEN GROUND". It may also indicate something else because the neutral is floating, I can’t remember for sure.

    If the unit is wired as a Grounded Power System the tester will indicate "CORRECT"

    Cheers,    
    Jim
    .
    lak

    3,554 posts    
    04-11-2019 7:08am

    I would think your isolation transformer would clean some of the grunge from the AC which would in return give you a darker background allowing you to hear more details within the music and perhaps deeper bass, provided you don’t overtax its rating. That’s what I experienced with my Xentek Extream Isolation Transformer (5 Kva) and weighed at least 100 pounds maybe more.

    +1

    Jim
    .
    Jim- thanks, easy enough to test and thanks for wading through my post. 
    I moved this unit in my second system where I don’t have a dedicated AC line but I also added Aric’s tube preamp to the mix and changed the amp’s power cord around the same time. The system is dead quiet and the bass is decent but I attributed most of that to the preamp and the power cord. I may try doing a comparison with the unit out of the loop using a power strip instead to see if I hear a difference.
    Thanks again for all the responses.
    It's a balanced power provider with a little surge and noise protection added.

    :)

    Nothing wrong with it, but it's' not going to regulate voltage.

    Best,
    E
    “...but it's' not going to regulate voltage.”

    Fair point. I said it puts out a constant 124v but this statement was false by definition since I’m not constantly measuring the output voltage. It does however put out 124v the few times I measured the voltage which was roughly 2-3 volts more when compared with its adjacent wall socket. 
    @kalali,
    Is that a loaded voltage or an unloaded voltage measurement? The greater the connected loaded the greater the VD (Voltage Drop) across the windings of the transformer.

    Measure the voltage with the intended load connected.
    .

    ^^^^^ Great question, and I think it was unloaded, if I remember correctly. I’ll take some measurement with preamp and amp up and music playing at moderate listening levels.
    @jea48 given the choice between the hospital grade Tripp-Lite and the regular Tripp-Lite that you referenced in your post, do you have a preference?  I am only concerned with front end equipment isolation i.e. low power requirement.
    I am only concerned with front end equipment isolation i.e. low power requirement.
    @testpilot ,
    Why? From what are you wanting to isolate?
    I want to isolate both my pre and phono stage from the main lines to reduce noise etc. On occasions, I also get a ground loop issue.  I run large power hungry mono block amp and I don't want to go the large transformer route. 
    Hi Test Pilot,
    The usual thinking is to use isolation transformers, but the owner of Jensen Transformers wrote an article about how this doesn’t really work. Your best safest bet are the semi-active ground lifters, assuming you have any issues at all.

    Best,
    E
    Thanks Eric, could you expand on the semi-active ground lifter comment. 
    I'm thinking of this:
    https://amzn.to/2Z7qun3

    $80 seems pricey though, see if you can find a cheaper version.

    But now that I think about it, Jensen Transformers also makes in-line RCA or XLR isolators as well. 
    Best,
    E
    testpilot

    258 posts
    04-12-2019 7:44am

    @jea48 given the choice between the hospital grade Tripp-Lite and the regular Tripp-Lite that you referenced in your post, do you have a preference? I am only concerned with front end equipment isolation i.e. low power requirement.

    My Choice?
    The regular Trip-lite unit as you call it. The "Grounded Power System", isolation power transformer unit. The grounded isolation transformer still provides isolation from the mains AC power grounded power system.


    An Isolated Power System, (IPS).
    The secondary winding of the isolation transformer floats above ground. Therefore there is not any reference from the ungrounded legs, leads, of the secondary winding to ground.

    For this discussion the IPS is a plug and play unit. It has a 3 wire power cord and grounding type plug. The wall AC power outlet equipment ground is connected to the metal enclosure of the IPS via the equipment grounding conductor of the power cord. The ground contact of the receptacle outlet/s that are connected to the output of the IPS connect to the equipment ground/chassis ground. There’s that AC mains power equipment ground!

    Say you connect a CDP to the IPS that requires the use of a safety equipment ground. What happens if there is a wiring fault from the fused conductor to the chassis of the CDP? ....... If the fault is a bolted fault, (an unintentional solid conductor/wire to chassis connection), the conductor becomes a grounded conductor, a neutral. Will anything happen from the electrical fault event? Will the CDP fuse blow? NO..... Nothing will happen. You the user, will not know the internal fault happened.

    Worth noting, as long as the ground faulted CDP is plugged into the IPS unit the small slot contact on the receptacle outlet/s (normally the HOT contact) will make that leg, lead, of the secondary winding the grounded conductor, the neutral. (The CDP makes the IPS unit an unintentionally Grounded Power System.) What happen to that total isolation of IPS?

    What happens if another piece of audio equipment is connected to the IPS? Say an integrated amp. Will there be any electrical problems because of the ground fault in the CDP? Will any sparks fly? No, as long as there are not any problems with the AC power wiring inside the amp.

    When the amp is plugged into an outlet on the IPS unit the normally hot conductor in the power cord becomes the neutral conductor. The normally neutral conductor of the power cord becomes the Hot conductor. (I am not going to address here how reversed AC polarity feeding the primary winding of the power transformer, of a piece of audio equipment, can affect the sound of the system.)

    So because of the ground fault condition inside the the CDP the normally Hot contact on the receptacle outlet/s, of the IPS, is now the neutral, the grounded conductor.(If a voltage test is taken you will measure zero volts from the normally Hot contact of the outlet to ground. If you measure for voltage from the normally neutral contact on the outlet to ground you will measure 120Vac nominal. Reversed AC polarity.)

    What if the CDP ground fault is after the ON/OFF power switch? When the CDP switch is closed the contact on the outlet of the IPS is grounded. When the power switch on the CDP is open the normally hot wire on the power cord is no longer grounded by the CDP ground fault.

    Is the secondary of the IPS floating above ground again? Not 100%. Why? Two things come into play. The primary windings of the two power transformers inside the CDP and amp. And don’t forget the interconnects that connect the CDP to the amp. Now the normally neutral contact on the outlet of the IPS is the neutral, the grounded conductor. Confusing? None of this happens with a "Grounded Power system" .... The HOT conductor is always the Hot conductor and the Neutral conductor, (The Grounded Conductor), is always the Neutral conductor.

    I could go on, but this post is long enough!

    IPS units should only be used under the direct supervision of qualified trained personnel. They are not Listed/approved for use in a residential dwelling.

    Jim.

    .
    Took some measurements. The voltage in the adjacent socket is 118.8v. With everything plugged into the transformer; streamer, DAC, preamp, and amp, the voltage out of the transformer is 122.4v +/-0.1 volts without anything turned on. With everything turned on the voltage stayed exactly the same with or without music playing even at high volumes. I had seen 124v in the past but I'm guessing it depends on the time of day where the voltage from the wall socket was closer to 120v. So it looks like the difference is roughly around 3.5-4 volts. On surface, the unit (1400VA according to the label) appears to be maintaining the same voltage regardless of the load, at least in my system.  
    By the way, this is what TSi Power says on their website:
    "An isolation line conditioner can eliminate the need for a dedicated circuit or expensive rewiring. This is particularly helpful when wiring is old or a tenant doesn’t have easy access to distribution panel boards."
    kalali OP

    1,684 posts
    04-12-2019 1:07pmT


    ook some measurements. The voltage in the adjacent socket is 118.8v. With everything plugged into the transformer; streamer, DAC, preamp, and amp, the voltage out of the transformer is 122.4v +/-0.1 volts without anything turned on. With everything turned on the voltage stayed exactly the same with or without music playing even at high volumes

    You said the transformer is rated at 1400Va. 1400 / 120V = 11.7 amps. If you did not experience any VD when everything is turned on that indicates the combined loads of your equipment is below 80% of 11.7 amps.
    As for the output voltage of the transformer. 122.4V to 124V is considered on the high side. 122.4V marginal, 124V is high, imo.

    I would check the nameplate voltage rating for the equipment you have plugged into the transformer. If it is 115V, 124V is too high in my opinion. 122.4V is pushing it. At 124V you have zero room for an overvoltage event on the AC mains, imo.

    .
    Look at the data plate on the isolation transformer unit, What does it say for input voltage, or it might say line in voltage? Does it possibly show more than one line in voltage? Like 115V, 117V, 120V? If so the transformer may offer different primary winding voltage line tap connections.

    What does it say for line out voltage, or output voltage?


    Last but not least. Is the unit an Isolated Power System or it wired as a Grounded Power System?
    .