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#67111 06/26/06 11:04 PM
Joined: May 2004
Posts: 116
Ok, this is my "dumb" question of the day:

When you go to the main CB panel (residential, commercial, or industrial setting), how do you tell if the feed is from a Wye or a Delta?

I'm either going to learn something new... or I'm going to feel pretty "stupid" when I get the answer from you all. (hey, I've felt stupid before)


#67112 06/27/06 04:23 AM
Joined: Aug 2001
Posts: 7,520
I would think a combination of visual examination and voltage readings would do the trick.

If there's no neutral conductor on the service bonded to ground, it must be delta.

If one conductor is grounded and there are only two other service conductors, it will be a corner-grounded delta, and you'll get the same voltage reading between the two hot legs and from each hot leg to ground.

If there are three conductors plus a grounded neutral, it could be wye or 4-wire delta.

Wye will show the same voltage from each phase to ground; 4-wire delta will show the characteristic "high leg" voltage on one phase.

#67113 06/27/06 06:00 AM
Joined: Dec 2004
Posts: 1,064
No such thing as a "stupid" question, if it is asked....

If you don't ask, how are you going to get the answer?

I agree with pauluk, voltage measurements would do the trick.

Do a search in the theory section under wye and delta. The guys here were nice enough to post schematics, and voltages for everyone to use. Take a look and ask away....

#67114 06/27/06 09:59 AM
Joined: Jul 2002
Posts: 8,432
Likes: 3
Just like a lot of other things, the Americans are conveniently backward.
Delta-Star Tranny's are used here to supply LV 400/230V installations.
No bad combinations, no 120/240/277/460/480, you name it combinations, why does the US always have to be a PITA and be different??.
The rest of the world is 50Hz, Grow up!!.
And don't get me started on Metrics.

#67115 06/27/06 11:44 AM
Joined: Jul 2004
Posts: 625
...why does the US always have to be a PITA and be different??.
Maybe, because we did it first, and other folks decided to be different from us?

#67116 06/27/06 11:56 AM
Joined: Jul 2004
Posts: 9,788
Likes: 14
Maybe it is because we have had electricity longer. You guys have been dealing with it, what? 60 years or so? When was it that the US Army wired up that place?
;-) sorry

Seriously, part of the problem here is that we have reminants of the Edison vs Westinghouse wars from the early 20th century and some folks won't change. We are lucky not to have DC grids.
Once you come down off the national grid the local power companies are free to offer whatever they want or whatever the customer wants. You can make a case for any of the various schemes that enter buildings.
Life might be easier if we did have a single national standard for services but then the IBEW would lose some of the mystique that makes it the sectet society it is.

Metrics is another whole question. That is a commie plot and we think the French were behind it. ;-)
Some believe it was just a way to charge the same for a smaller bottle of whiskey. (750 vs a "fifth")

Greg Fretwell
#67117 06/27/06 03:51 PM
Joined: Jan 2003
Posts: 4,391

Delta-Star Tranny's are used here to supply LV 400/230V installations.
No bad combinations, no 120/240/277/460/480, you name it combinations,

Can you tell me why any of those combos are any better or worse than another?

Is it not better to pick a voltage for conditions than to be locked in with only one option?


[This message has been edited by iwire (edited 06-27-2006).]

Bob Badger
Construction & Maintenance Electrician
#67118 06/27/06 04:04 PM
Joined: Dec 2001
Posts: 2,498
I don't think the voltages themselves are a problem - but arrangements like corner grounded delta or 4 wire delta do seem somewhat overly complex for people who see on a dailoy basis you can live perfectly with 4w wye supplies and loads that are either connected in wye or delta.

#67119 06/27/06 07:55 PM
Joined: Mar 2005
Posts: 1,213
The rest of the world is 50Hz, Grow up!!.
Man, don't get me started on 50Hz! I work sites all around the world, and every time we have 50Hz it's a headache. The voltages aren't that big a deal, but having to derate all these UPS systems because the magnetic flux is saturating the transformer core is just killing me... Wanting a 750kVA and having to pay for a 750 but only getting a 625, man, it hurts. Can't even throw money at 'em to rewire the transformers with a different core because the 50Hz transformers are too big! 60Hz is 20% more efficient, why don't ya'll just give it up and switch to 60Hz? All your motors and transformers would be smaller and cheaper ya know!

The worst is when there is a mix of US and european voltages and frequencies, that tends to get messy...

[This message has been edited by SteveFehr (edited 06-27-2006).]

#67120 06/27/06 08:52 PM
Joined: Jul 2004
Posts: 9,788
Likes: 14
I think corner delta is one of the best solutions out there. If I just have 3 phase loads I can do the whole thing with 2 pole equipment that basically looks/costs like single phase.
We did a lot of pumping stations this way.
You just need to be sure it gets serviced by qualified people who know what is going on.

Greg Fretwell
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