ECN Forum Forums General Topics of the Trade General Discussion Area Wye or Delta?

Electure,
I think John (renostienke) bought up panel marking some time ago.
I'm all for labels that we all can read, not just the person that wrote them, after all, whose to say that he/she is going to be there to read them next week, next month or in fact next year?.
I used to use a Brother(Shameless advert I know, but you get the drift) label-maker, if you can't read the labels from one of them, you need help and fast!.

{message edited for bad spelling}

[This message has been edited by Trumpy (edited 06-30-2006).]

The deal with the picture I posted is this......
A 120/208 system is a Wye, and there is no leg with a higher voltage to ground/neutral. The system pictured is a 120/240 3Ø 4W Delta.

The Code requirement is that the Ø with the higher voltage be used as the B, and not the CØ.

Like Gfretwell said, you have to have qualified people. (the same could apply to a duplex receptacle)This one obviously wasn't, but also saw fit to write "Installed by", with his name, on another part of the panel.

Doing electrical measurements between phases to ground will help you accomplish what you are trying to achieve. i prefer wye in most commercial/industrial applications myself because of the load balancing characteristics you are able to achieve with it, however Delta 4 wire systems also has a distinct advantage over wye systems in that if one transformer is lost in the utility bank, you can always T the other two and still achieve a three phase system. Corner Ground systems should just be done away with completely. We owe our gratitude to Mr. Nikola Tesla for three phase. And as far as the rest of the world, well..........Just steal the information and copy us, that's what youre truly good at.

Why?

A few links:
http://www.teal.com/products/App%20note%20AN-15.htm
http://www.phaseconverterinfo.com/phaseconverter_delta_wye.htm
http://www.federalpacific.com/university/transbasics/chapter3.html

Reading the labels can give you a clue, but always measure. I recently found a 208 3-phase receptacle that was wired up as a single phase for 8 years, feeding a 3-phase transformer. That really made for some strange measurements and head-scratching...
/mike

*** BUMPING THIS THREAD UP AGAIN ***

Just wanted to bump this up again, since the information is really interesting and may be of assistance to others.

Scott35

scott35, i have a transformer connection manual that shows the hi leg of a 120/240 volt delta on "C" phase always. but you say code says should be "B".wonder why the difference? BTW it's a GE transformer connection manual. one other ? why is the hi leg 208?

Let me throw in my two cents... not that I disagree with anyone (I don't), but my approach is a bit different.

When I open a panel, I first look at the lugs. Two hot wires = single phase. Three hota and it's a three-phase.
Now, is there a neutral?

Checking volts line to line, "240" suggests delta. "208" suggests wye.
Checking volts line to ground. Does every leg have the same reading? If not, it's a delta. One "high" leg, and it's got one transformer winding grounded in the center, to make the "neutral." One leg reading "0", and it's a 'corner grounded.'

Now, look at the pole. One big, and two little transformers... the big one has the center tap for the "neutral." Two transformers, and it's an "open delta." One transformer, and it's single phase.

Know your "nominal" voltages: 120, 208, 240, 277, 480. If any of your reading vary from these by more than, say, 5%, there's something goofy happening.

The only problem with your method is a corner ground may present you with 2 blacks and a white with 2 pole breakers.
It looks like a garden variety 120/240.
Line to ground will be 240v. That is the tipoff. It should also be labelled if the installer wants to help the next guy.
The first one I saw confused the hell out of me. Three transformers, 3 phase motors and single phase <looking> equipment. I was there alone so I got out my trusty meter and figured it out before the other guys got there and I had a chance to say something dumb.