Tripp Lite Isolation transformer *not* an isolation transformer

[Speakerguy]

OK, so I bought this isolation transformer. It arrived today and guess what?

IT'S NOT AN ISOLATION TRANSFORMER.

Output ground to wall ground resistance: <1 ohm. Output Neutral to earth ground: <1 ohm. Output isolated "line": 125VAC to earth ground. Output isolated "neutral" to earth ground: <10mVrms.

So no isolation, and mediocre regulation for a 1kVa unit, and the mounting rails came bent on top of that.

They better pay for return shipping. Ridiculous.

 

[rezer]

It sounds more like a defective unit. Hard to believe that something as critical as this would have such a design flaw.

 

[mneary]

If I look at the data sheet, it looks like you received exactly what they described:

"Secondary neutral to ground bonding eliminates common mode noise"....

Maybe there's a simple way to open that bonding.

 

[Speakerguy]

I asked about that exact line in the data sheet in a previous thread, but the second half of the sentence you quoted states "isolated ground" and the consensus was that it was likely a true isolation transformer. So I was unsure of what I would get. But apparently this is just a surge suppressor and noise reduction device, and in no way provides the isolated ground it claims.

In any case, it came damaged.

 

[Ubergeek63]

I suspect it is a true isolation transformer, and you are simply confused as to what that means.

The output is SUPPOSED to be connected to earth ground. Common mode noise my ass! It does help common mode noise but the REAL reason is safety! Equipment is grounded so you don't get shocked when you touch it.

Dan

 

[Speakerguy]

An isolation transformer where its ground and neutral are at earth potential is most definitely not an isolation transformer, in the electronics repair usage of the term.

Maybe it is an isolation transformer from a line noise reduction point of view. But in electronics, an isolation transformer won't kill you if you accidentally grab the 'hot' line and are connected to earth ground. It will only kill you if you grab its 'hot' and 'neutral' lines at the same time and you make the connection across the secondary windings.

By having the output neutral and ground at the same potential as earth ground, it offers no safety advantage over working with line voltage directly.

 

[Speakerguy]

This is what Sir Nigel had to say about it in a previous thread (my question his answer):

Question: If an isolation transformer has its secondary neutral connected to earth ground, how is that protecting me?

It wouldn't be, and that isn't how a transformer should be used - as you say, it completely removes any usefulness of the transformer.

 

[Hero999]

I agree.

Have you connected this thing up and measured the output votages between earth and the line conductors?

Some isolation transformers are centre tapped because it reduces common mode noise.

 

[Speakerguy]

Yes, it was 125VAC from line out to earth ground and <10mVrms from neutral out to earth ground. No centertap, and neutral out is tied directly to earth ground.

 

[Hero999]

That's pretty pointless then.

The only reason why you would use it is to remove the RCD protection from a power outlet which isn't safe - you're better off without it!

 

[Pommie]

I'd want my money back + shipping. Isolated means no connection to the primary. Do they have something equivalent to the trades description act in the U.S.?

Mike.

 

[Speakerguy]

We have some consumer protection laws here, but most of our laws are written by the corporations (google what they did to our bankruptcy laws a few years ago, and the DMCA, etc). I should have no problem getting my money back on the item, but shipping is another matter entirely.

About the only consumer protection laws here that have any teeth are the tenancy laws, and those vary by state (I'm in Texas).

 

[Ubergeek63]

We have some consumer protection laws here, but most of our laws are written by the corporations (google what they did to our bankruptcy laws a few years ago, and the DMCA, etc). I should have no problem getting my money back on the item, but shipping is another matter entirely.

About the only consumer protection laws here that have any teeth are the tenancy laws, and those vary by state (I'm in Texas).

Not gonna happen, even the data sheet from the link you supplied explicitly states that the neutral is earthed.

 

[Speakerguy]

Not gonna happen, even the data sheet from the link you supplied explicitly states that the neutral is earthed.

It also specifically states that the the ground output is and isolated ground in the exact same sentence where you read neutral to ground bonding. Is that the ground lug on the output side, or the ground lug on the input side? It says two potentially conflicting things. Like I said, that was why I was unsure as to what I would get.

Besides, the unit was damaged in shipping.

 

[Hero999]

If it's damaged in shipping they might not give you a refund because it's no their fault. To get compensation you'll probably have to claim off the insurance.

If you can't get your money back, then you could open it up and disconnect the earth from the secondary but the insulation between the primary and secondary might not be class 2 in which case it doesn't fulfill the safety requirements for an isolation transformer.

 

[Speakerguy]

Actually, since they were the ones to pay for the shipping (they billed me for it, but they paid for the shipping label) the service was rendered to them and they are the ones that have to file the claim. That's the way it works here in the US with UPS shipping service.

In any case, Allied gives you 3 days to refuse an item, so I should be in the clear.

Also, while consumer protection laws kind of suck in the US, I paid for it with a credit card. Credit cards give you a LOT of buyer's protection. If all goes to hell, I'll just initiate a chargeback.

 

[rezer]

You got what you paid for. What you have IS an isolation transformer. This is a shielded iso. transformer that uses Faraday shielding for noise immunity between the primary and secondary. This transformer incorporates common-mode rejection. In fact, any iso. transformer on the market will have neutral-ground bonding. This is standard and prescribed by the NEC. The N-G bond is there for your safety. Without it, your system won't be able to detect ground faults. Below is a link that explains the ground-bonding really well.

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

Ubergeek63 is right. The documentation clearly states what you have. It states that it has a neutral-ground bond "...with isolated ground reference." This means that the N-G bond is isolated from the AC neutral line by being bounded on the secondary side going to earth ground, as NEC requires.
And let's not forget, the first thing I looked for in the spec sheet was a UL listing. It is listed, according to the specs. There should be a label somewhere on the unit. With the UL label, that pretty much seals it as an isolation transformer.

 

[Speakerguy]

Well, they are trying to make me pay return shipping. I think they are forgetting it was received damaged. I should hear back from them tomorrow, as it's after business hours now.

Besides, I don't need to argue what an isolation transformer is. If the NEC mandates that this is how they function, then isolation transformers don't exist as they once did.

 

[Hero999]

You got what you paid for. What you have IS an isolation transformer. This is a shielded iso. transformer that uses Faraday shielding for noise immunity between the primary and secondary. This transformer incorporates common-mode rejection. In fact, any iso. transformer on the market will have neutral-ground bonding. This is standard and prescribed by the NEC. The N-G bond is there for your safety. Without it, your system won't be able to detect ground faults. Below is a link that explains the ground-bonding really well.

Are you sure?

I don't know about the US standards but the UK standards don't mandate that the neutral needs to be bonded to earth. A floating system is called an IT earthing system and is common in hospitals and other areas where tiny earth leakage currents can cause problems.

I reckon you should buy a medical grade transformer which should have the secondary neutral isolated from earth.

 

[rezer]

Are you sure?

I don't know about the US standards but the UK standards don't mandate that the neutral needs to be bonded to earth. A floating system is called an IT earthing system and is common in hospitals and other areas where tiny earth leakage currents can cause problems.

I reckon you should buy a medical grade transformer which should have the secondary neutral isolated from earth.

You "reckon"! If you didn't mention you were from the UK in your post, someone my mistake you for an American (a southern boy of course).