Transformer installation

[benaround]

Templdl,

I can't recall seeing a transformer that on the nameplate didn't say

primary xxxxxxxx

secondary xxxxx

For this reason alone, as I have stated in the past, I don't like 'back feeding'

transformers.

The kicker here is some of these trannys have in their instructions, some of

the cautions to follow if 'back fed'.

For the record, I'm with Brian on this issue.

What does the trans. manafacture have to lose? if it goes bad, you get to

buy another one.

 

[iwire]

I can't recall seeing a transformer that on the nameplate didn't say

primary xxxxxxxx

secondary xxxxx.

Frank, you need to look around more, I have not seen one lately that did say that.

 

[iwire]

Jim: PLEASE, most electricians have NOT A CLUE. I get calls all the time regarding this issue, how to, why.

Even if I accept that to be a fact......prohibiting an installation that can be done safely is definitely not the right solution.

You also do not know about all the ones that are in service without any issues.

The fact you get called is more about how good your reputation is, and that is a good thing.

 

[brian john]

Bob:

I do not want to prohibit this installation, I just feel if this is a for sale issue, customer needs 480 and only has 208 available the customer is better served with a 208 delta to 480/277 Wye xmfr.

I keep a fairly wide range of transformers for temporary and testing. Especially when we need a bypass of a UPS with a non standard phase shift. I have had to step it up and down to get around this, but this is generally for temporary.

 

[benaround]

Bob,

Without that info, how would you know what you are working with ?

Our shop use Siemans most of the time and I'll guarantee you they have

a nameplate with 'pri' and 'sec' voltages printed on them. Transformers

are part of every job we do, and that's as far as I have looked.

 

[480sparky]

Here's a pix of a transformer label I think you guys are talking about:

 

[iwire]

I'll guarantee you they have

a nameplate with 'pri' and 'sec' voltages printed on them.

No, they have high and low voltages marked on them, no reference to which is primary and which is secondary.

Go right to Square Ds FAQ page and they will tell us straight out that for other then control transformers that their transformers may be back fed.

 

[iwire]

Bob:

I do not want to prohibit this installation, I just feel if this is a for sale issue, customer needs 480 and only has 208 available the customer is better served with a 208 delta to 480/277 Wye xmfr.

Well then we have to remain in disagreement. :smile:

There are cost and time issues that you are choosing to ignore.

Given my choice I would always use the 'right' transformer but I will do what it takes to get the job done within the code and on time. If that means back feeding and corner grounding then thats what it means.

 

[brian john]

Bob: Maybe I am spoiled I can get a 208 delta transformer by Thursday, delivered to my shop if I order it on Wednesday.

 

[benaround]

480 sparky,

I'd like you to go to the Siemens web site and post the same picture of

their nameplate as you did for SqD. I would, but I never have, thanks.

 

[nakulak]

Bob: Maybe I am spoiled I can get a 208 delta transformer by Thursday, delivered to my shop if I order it on Wednesday.

sweet .

 

[templdl]

Is there a right way or a preferred way?
You can supply a 208Y side of a 408D-208Y/120 configured transformer to the 480v delta. Is it right or wrong? As long as it complies with the NEC there's no problem. As such one can?t say it is wrong.
However, is it preferred? Probably not. If a 208D-480Y/277 was readily available I personally would go with it.
I any case it's not that it's a 208Y or 208D on the side that?s being supplied its how a 480v delta is to be protected and configured/grounded as compared to a 480Y/277

 

[frenchelectrican]

Genrally i dont have much issuse with reversing the power transformer but keep in your mind is the inrush current [ as what other did mention there ] and you have to unbonded the 0X connection otherwise it get weird reading on that.

Myself i did check few transformer manufacters FAQ's and they stated it can be reversed feeded without much issue but a minor qurik is you wil not get the excat voltage what you want.

Merci, Marc

 

[iwire]

Bob: Maybe I am spoiled I can get a 208 delta transformer by Thursday, delivered to my shop if I order it on Wednesday.

I think that if tried that on a regular basis you would be disappointed.

The shop I worked for did 140 million a year and still we might have trouble getting oddball stuff.

Brian I really don't get the point of this thread.

You say you don't want to prohibit it so is the point of this thread just a way for you to complain about an installation that can be done perfectly safely but just bothers you?

You say the customer 'is better served' with a delta delta, well I have not met a customer yet that really cares how I do it, as long as it works, it is safe and it is within code.

Oh I know you work for a lot of clients that do care, but if choice comes down to be offline longer or back feeding a transformer I don;t think they are better served by delaying them just to avoid back feeding a transformer....legally.

BTW...personlly I have only back feed one delta-Wye and that was for a temp feeder.

 

[brian john]

Bob over the years I have replaced several (3) of these BACKFED systems, 2 at universities and 1 at a hospital. These are places that have on staff personnel and they were befuddled. I have found these with burnt neutrals, connected neutrals that were grounded at the transformer. And while this makes cash for me, it is just a place where I feel the end user would be better served with a different configuration, remember you are not the NORM in our industry.

My point is and strictly my opinion the better system for a variety of reasons is a 208 delta to 480/277 Wye.

 

[wasasparky]

...I have found these with burnt neutrals, connected neutrals that were grounded at the transformer...

Were the neutrals properly sized?
Would a properly sized neutral get burnt? why?

I personally would not connect the neutral, but have never fully understood why it is really a bad idea...