On Fri, 05 Jan 2018 11:37:20 -0500, wrote:

On Fri, 5 Jan 2018 05:34:25 -0500, "Mr. Luddite"
wrote:

I agree the harmonic problem is just on wye but that is the most
common configuration, 208 or 480.
I think the problem first showed up on 480/277 wye systems where they
had a building full of 277v electronic ballasts.
Then it started showing up in those 208 systems that were feeding 120v
lines in cubicles through the internal wiring with a 5 wire feeder as
PCs started replacing terminals with ferro power supplies and space
heaters.

Delta is always funny stuff, depending on where or even if you land
the ground. Corner grounded is probably the easiest to confuse the
novice. It will look just like single phase until you get your meter
out. (2 pole breakers, white wires etc)


Not familiar with that. The majority of the systems we built were
designed to run on 480v, 3 phase. All the main breakers, fused
disconnects, motor starters, etc. were three pole. Ground was run
separately. We used a dedicated control transformer in each power
cabinet to generate whatever the low voltage control wiring was ... 120v
in the early days but later 24 volt. IIRC, the control transformer on
the 120v systems was a 480v/240v step down with a center tap, providing
a neutral.




Did you ground your 480 delta at all? If so where did the ground land?

I understand your control circuit voltage can be 120 if you want. That
is just a class 1 control circuit. Most people are familiar with class
2 but they are both controlled by the same article in the NEC.
Class 1 just looks like regular line voltage circuits because it is
not voltage or current limited like class 2 and 3.
The center tapped 240 delta is commonly called "red leg" or "wild
leg"because the corner between the center tapped windings will be 208v
to ground. "Red" is a misnomer tho because the NEC requires the wire
to be orange. That is very common in places where they want discount 3
phase and have a significant amount of single phase loads like those
small industrial bays. The PoCo can do it with 2 transformers,
generally the wild leg will be on a much smaller one. One "winding" is
actually open. hence another name, "Delta Veep".

http://gfretwell.com/electrical/red%...ansformers.jpg

99.99% of the time, if you see 3 transformers on the pole, it will be
wye. but I have seen one place in Key West where they had red leg
delta with 3 transformers. The only tip off was one was bigger than
the other two and it was confirmed by analysing the wiring.
http://gfretwell.com/electrical/Tran...%20_breath.jpg

Yeah my wife thinks I am crazy too, taking pictures of transformers.



===

Remind her that it could be worse, like taking pictures of half n'ked
babes at the beach. :-)


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