Tripp Lite Isolation transformer *not* an isolation transformer

[Hero999]

Reckon is a common word in the UK as well.

My location is clearly mentioned in my profile and displayed next to my name unless you thought I was in New England but that's the north not the south.

 

[rezer]

Reckon is a common word in the UK as well.

My location is clearly mentioned in my profile and displayed next to my name unless you thought I was in New England but that's the north not the south.

No, I knew where you were from. I mentioned the south because it is predominantly used there. I didn't know reckon was used in the UK, perhaps that's where we acquired it.

 

[HiTech]

Did any of you read the .pdf on the item?
https://www.electro-tech-online.com/custompdfs/2008/09/TRIPP-LITE_POWER-PRODUCTS_5752502PDF.pdf

At numerous points of the description it states "complete line isolation". A bonded neutral with an isolated ground should render the secondary as being isolated from the primary. If this is so I would suspect something is wrong with the unit. Tripp-Lite produces high quality items and they stand behind their products, in my experience.

 

[rezer]

Did any of you read the .pdf on the item?
https://www.electro-tech-online.com/custompdfs/2008/09/TRIPP-LITE_POWER-PRODUCTS_5752502PDF-1.pdf

At numerous points of the description it states "complete line isolation". A bonded neutral with an isolated ground should render the secondary as being isolated from the primary. If this is so I would suspect something is wrong with the unit. Tripp-Lite produces high quality items and they stand behind their products, in my experience.

Well, UL evidently stands behind them also. To me, and maybe my thinkings off here, earth ground and neutral secondary are not part of the primary windings. Would this not be isolation? I read the .pdf and it clearly notes the N-G bond. As does every other article I've come across.

 

[Nigel Goodwin]

Well, UL evidently stands behind them also. To me, and maybe my thinkings off here, earth ground and neutral secondary are not part of the primary windings. Would this not be isolation? I read the .pdf and it clearly notes the N-G bond. As does every other article I've come across.

I've no idea what it's supposed to be for?, it sounds pretty pointless?.

An isolation transformer as I understand it (and as he wants) provides a completely isolated secondary, so the item plugged in to it floats away from earth. This is for safety reasons, and means you can't get a shock to earth, and it allows you to use earthed test equipment.

 

[rezer]

I've no idea what it's supposed to be for?, it sounds pretty pointless?.

An isolation transformer as I understand it (and as he wants) provides a completely isolated secondary, so the item plugged in to it floats away from earth. This is for safety reasons, and means you can't get a shock to earth, and it allows you to use earthed test equipment.

Everything I have read indicates the secondary neutral is tied to earth groung for safety reasons. This give the current a place to go. Now I would tend to agree with you. This is not how I remember isolation transformers being constructed either. There was no ground connected to the primary side. I don't know if you had a chance to read the below article that I posted earlier but here it is. Tell me what you think about the N-G bond.

https://www.electro-tech-online.com/custompdfs/2008/09/mw20ng20article-1.pdf

 

[ecerfoglio]

Everything I have read indicates the secondary neutral is tied to earth groung for safety reasons. This give the current a place to go. Now I would tend to agree with you. This is not how I remember isolation transformers being constructed either. There was no ground connected to the primary side. I don't know if you had a chance to read the below article that I posted earlier but here it is. Tell me what you think about the N-G bond.

https://www.electro-tech-online.com/custompdfs/2008/09/mw20ng20article-2.pdf

The problem is that the words "isolation transformer" are used to describe to diferent things:

>> An isolation transformes to give an "isolated" enviroment so you can service line operated devices, use grounded test equipment, etc. (This is what most of us are thinking when we say isolation transformer)

>> A surge protector used to power sensitive equipment (computers), and that happens to be a transformer. They call it "isolation transformer" because it isolates the load from the line's noise, but it doesn't provide earth isolation.çç

 

[rezer]

The problem is that the words "isolation transformer" are used to describe to diferent things:

>> An isolation transformes to give an "isolated" enviroment so you can service line operated devices, use grounded test equipment, etc. (This is what most of us are thinking when we say isolation transformer)

>> A surge protector used to power sensitive equipment (computers), and that happens to be a transformer. They call it "isolation transformer" because it isolates the load from the line's noise, but it doesn't provide earth isolation.çç

Yes, and I believe that is correct. The documentation makes it clear that the isolation xformer uses Faraday shielding which is what I mentioned earlier. However, the N-G bond is the issue. With the presense of this bond, does it in anyway take away the safety of the device? The primary hot/neutral are isolated from the secondary and anything I've looked at clearly indicates that the secondary neutral must be bonded to earth ground. This provides an avenue for risidual current that could be in the equipment. That is my understanding of it. A non-compliant bond would be a bond from neutral to earth ground inside the electrical box at the service entrance. This means the primary neutral would be earthed, which is not the case. What say you?

 

[Hero999]

Everything I have read indicates the secondary neutral is tied to earth groung for safety reasons. This give the current a place to go.

Bonding the neutral is both good and bad.

Bonding the neutral ensures that it's at earth potential. If the neutral is floating it could be at all sorts of dangerous voltages, for example if it's supplied by a three phase transformer and there's an earth fault on one of the phases, the neutral will float at the phase voltage and the other phases will float at √3 * phase voltage. Even worse, if a step-up auto transformer is connected to the output of the transformer and an earth fault occurs on the live side of the secondary, the neutral will float at a higher voltage than the normal mains voltage whcih could cause the insulation to break down.

For the above reasons an IT (isolated from earth) system isn't normally used for electrical power distribution and the electrical codes forbid connecting autotransformers to the output of such a system.

As has already been stated, an IT system has the advantage of only been able to shock if the person is in contact with both the line conductors. For this reason isolation transformers are often used in hospitals, on building sites and test benches where there is a high risk of electric shock. In fact isolation transformers are actually mandated in operating theatres where the slightest leakage current could harm the patient and RCDs cause reliability problems.

In some cases an earth fault detection circuit that measures the impedance between the secondary and earth is used with an isolation transformer which activates a warning when an earth fault occurs.

 

[mneary]

Grounding philosophy is interesting reading, but unrelated to Speakerguy79's original objective. Speakerguy79 wants a transformer that allows him to operate a device without a ground reference. Many off-line devices make this a concern, because their 'ground' of its power supply is otherwise at something like -165V.

Is such a device currently available? Can his existing unit be converted?

 

[rezer]

Grounding philosophy is interesting reading, but unrelated to Speakerguy79's original objective. Speakerguy79 wants a transformer that allows him to operate a device without a ground reference. Many off-line devices make this a concern, because their 'ground' of its power supply is otherwise at something like -165V.

Is such a device currently available? Can his existing unit be converted?

If there is, I haven't found any.

 

[Nigel Goodwin]

If there is, I haven't found any.

Check RS Components, they have at least four pages of isolation transformers which provide proper safety isolation as required.

 

[rize]

Hi Speakerguy79,

Back in 07' your complaint and arguments I thought were well grounded I found the subsequent replies to your posting very helpful and important to anyone needing complete isolation from AC mains. I'm curious how you resolved your issue and what type of product did you end up using?

BTW I ended up buying the following product;

**broken link removed**

The description of this unit is very specific about your original complaint.

"On all the International/Multi-Voltage models, the secondary neutral conductor is NOT grounded."

Thanks again,
Rize

 

[Hero999]

Yes, they do exactly what he wants, they're medical grade isolation transformers as I mentioned above.

They're very expensive though, much cheaper non-medical isolation transformers designed for test benches and building sites can be found.

 

[rize]

Yes, they do exactly what he wants, they're medical grade isolation transformers as I mentioned above.

They're very expensive though, much cheaper non-medical isolation transformers designed for test benches and building sites can be found.

Toroid.com sells direct to public and is expensive. I got mine on eBay from a medical equipment reseller considerably cheaper. I contacted toroid.com once and they were very DIY friendly.

I wonder if speakerguy contacted tripp-lite with his concerns?

So if IT's secondary neutral not grounded, implies hot & neutral must be touched simultaneously to receive a shock. Is this true for DUT's with 2 and 3 prong power chords?

I think I understand complete isolation from commercual AC with 2 prong DUT's but things get slightly more complicated with 3 prong DUT's simply because another variable is introduced.

Doesn't a 3 prong DUT connected to IT's secondary share the same Ground with commercial AC? If yes, this wouldn't be 100% isolation unless the tester leaves the IT's secondary ground pin open. I heard technicians do this to be 100% isolated but doesn't this defeat a safety measure against the possibility of a hot chassis?

Thanks

 

[Hero999]

What's a DUT?

 

[Nigel Goodwin]

What's a DUT?

Device Under Test

 

[Hero999]

As far as I'm aware, the general practice is to leave the case of the device unearthed but if they're multiple devices connected to the same transformer, their chassis should be bonded together, to ensure they're at the same potential.

 

[rize]

What's a DUT?

Device Under Test

 

[rize]

As far as I'm aware, the general practice is to leave the case of the device unearthed but if they're multiple devices connected to the same transformer, their chassis should be bonded together, to ensure they're at the same potential.

You mean like Fig.1 in this B&K manual for TR-110 Isopack?

https://www.electro-tech-online.com/custompdfs/2010/05/TR-110_manual.pdf

This above actually is more confusing because the B&K diagram shows various test equipment ground connected to DUT's chassis which finally ends up in the Iso-packs secondary Ground receptacle. This does not seem to be 100% isolation from commercial AC. OTH how else could a tester protect himself from a hot chassis? Without using Iso-pack's secondary Ground, electricity can flow through the tester.