y to delta ...208v to 480v sec

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Re: y to delta ...208v to 480v sec

I recently did an installation as stated above. The ITE / Siemens installation guide does show wiring diagrams for a step-up installation. All terminal are labeled HV or LV, not primary / secondary. The installation was corner ground as agreed upon with the local AHJ. The main reason we chose to use a "Step down" transformer for this installation was delivery time as this was a stock unit and only 480 volt, 3 phase was required.

I am sure that major transformer manufacturers would not have publications on alternate wiring diagrams if not properly tested & listed for the application.

Most of my electricains have never seen a corner grounded installation and they were all amazed at the lack of explosion when energized.
 
Re: y to delta ...208v to 480v sec

mdm: Does the catalog, describing this transformer, include the instructions for reversing?

The delta winding is designed for 277 volts to ground. There will be 480 volts to ground with this mickey mouse design.(No offense intended to you), this is an individuals decision not an engineering standard.

The electricians do not need to learn how to perform a corner ground installation. A corner ground system is dangerous, and irresponsible to implement. They should never be used. There is much safer alternatives.

Section 110.4 Voltages. This section does not permit a higher voltage to ground, being applied on a winding, than intended by the design.

Furthermore...The UL listing instructions specify that approval to operate at an elevated voltage, must be marked on the transformer.

[ July 19, 2003, 02:21 PM: Message edited by: bennie ]
 
Re: y to delta ...208v to 480v sec

I installed a step up 208 to 480 transformer for a booster pump station. This transformer was about twice the cost of step down. The differecne is a step down is delta wye and a step also delta wye. it you reverse a step down then you have a wye delta with ungrounded secondary. Check a aq D catalog you will see that they make a step up.

I agree with Bennie if the instructions don't list it as being able to be wired, it would be a violation and probably a problem to do so.
 
Re: y to delta ...208v to 480v sec

Tom: Could you imagine an injury suit, where someone is injured by the 480 volts when it would normally be 277. We, of course, don't want to get hit by either one. But the law suit would be a slam dunk.
 
Re: y to delta ...208v to 480v sec

Many years ago, when I was working for the Air Force, I attended the product service schools at GE, and Acme Transformer Co.

One of the first things covered in the courses was to not reverse a delta/wye common core transformer. Separate single phase pots can be connected in any 3 phase configuration desired.

When I first heard that GE published a technical bulletin with instructions on how to reverse a transformer. I wrote to them and received a phone call from the head engineer of the design staff.
He agreed to modify the instruction bulletin to include the words "Consult NEC and UL for approval of reversing transformers".

The entire article should have been retracted, but to do so would be taken as admitting the original was wrong. The fear of liability suits forced them to continue being wrong. Go figure.
 
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