Isolation Transformers

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.

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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....

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

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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
.

@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.
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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
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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.

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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?
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