- Location
- Massachusetts
No
...but the course states, "...this connection... has the approval of most electrical codes."
Now I get it. :smile:
Even if it was current that is an odd statement.
No
...but the course states, "...this connection... has the approval of most electrical codes."
See page 22, figure 26A and the text immediately above the figure.
It says to essentially connect the supply neutral to the load neutral, bypassing connection to the midpoint connection of the BBXFMR.
NO, NO, NO.
Do not ever use the neutral of a 208Y/120 4wire system when creating a 3-wire buck-boost arrangement. There will be about a 60V difference between grounded neutral of the wye system and the the neutral point of the derived system. This also means that the derived system voltages will be about:
L-L = 236V
L-N = 118V
L-G = 133V (?)
N-G = 60V
It involves vector math.I am not seeing where this 60V difference is coming from. Can someone point it out real quick?
Okay, I see your point.
But to split hairs.
I said simply to never use buck boost to create a 3-wire 120/240 system. I inferred but did not state the problem was the derived neutral point.
The Square D literature, you correctly quoted, says:
If you need a 3rd wire get it from the original system not from the buck-boost. Square D definitely says do not make a connection to the derived neutral.
Square D does say that if you use a 120/240-12/24 buck boost the L-N voltage will be about 129V. The OP was using a 120/240-16/32 transformer so the L-N would exceed the +10% tolerance of a nominal 120V device.
I am not seeing where this 60V difference is coming from. Can someone point it out real quick?
Your link leads to the wrong publicationIt involves vector math.
Go to the Square D Study guide we have been discussing and look at page 21 figure 26.
http://ecatalog.squared.com/techlib/docdetail.cfm?oid=090089268007917c
It involves vector math.
Go to the Square D Study guide we have been discussing and look at page 21 figure 26.
http://ecatalog.squared.com/techlib/docdetail.cfm?oid=090089268007917c
One thing I've not seen mentioned is that tying the transformer "neutral" to the supply neutral also creates a timing issue, because the two halves of the B/B transformer share a single core.I agree with your assessment... I was just pointing out something I believed you missed.
Here's a direct link:
http://ecatalog.squared.com/pubs/Electrical%20Distribution/Low%20Voltage%20Transformers/Mini%20Power-Zone/I1(R1).pdf
No, it's interconnecting the secondary with the primary that makes a buck-boost into an auto-transformer.If I understand correctly the only difference between an Buck-Boost and an autotransformer is that a Buck-Boost is for single phase, and an Autotransformer is for 3-phase?
One thing I've not seen mentioned is that tying the transformer "neutral" to the supply neutral also creates a timing issue, because the two halves of the B/B transformer share a single core.
If two separate B/B transformers were used instead, it could work, except the primaries would then be receiving 120v, eliminating the need for the B/B in the first place. Can't win 'em all. :roll:
My point was that connecting the source neutral to the load renders it with 120-0-120v, the desired product, but with the same 208v and 120 deg. between the lines.Actually it wouldn't eliminate the need... because the two 120V sources are still 120? out-of-phase... but it would work (as in not let smoke out... there would still be voltage issues).
See above response.I don't think there would be a timing issue. Why would this be any different from taking two legs of the standard wye system.
Okay, no biggie, really. Maybe I've been over-complicating it. (Is that the same as under-simplifying it?)We have been down this road before, I will agree to disagree.
I agree no biggy
I don't know what I am missing here, but if the output and the input voltages match it should just power the transformer up. And I don't mean let the smoke out of it either.
One core or three cores shouldn't have anything to do with this.
Line #1 and Line #2 are just one phase not two. If your taking your power from those two legs only the other two phases play no part. The neutral of the three phase is just like the neutral of a single phase when just using two legs.
The only effect the three phase wye system has is the interaction of the three phase mixing and beating it down from 240 volts to 208 volts.