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- New Jersey
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- Journeyman Electrician
Where would the requirement for a GEC be in the NEC for an ungrounded Delta and where would you connect it?
4160 Delta Secondary Grounded or Ungrounded
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Where would the requirement for a GEC be in the NEC for an ungrounded Delta and where would you connect it?
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- Placerville, CA, USA
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- Retired PV System Designer
Metal parts likely to become energized, I imagine. As mentioned, the case of the step up transformer would be connected to the primary EGC, while the case of the step down transformer would be bonded to the GEC of the resulting separately derived system. If the run is connecting two buildings, IMHO there is no requirement to bond the two GESs together. If in the same building there must be a wire bond between all ground electrodes, probably in the form of an EGC connecting the two ends, even though there is no grounded conductor.
electrofelon
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- Cherry Valley NY, Seattle, WA
IT is analogous to a detached structure under current code with separate N-G. The GEC lands on the ground bar, but doesnt hit a conductor of the system. See 250.30(B)
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- New Jersey
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Sounds like a waste of time. There are 8-500 kcmil EGC's run to the primary and since the secondary is #2 a #8 GEC landed with those 8-500's would be a joke. 
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- Illinois
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- retired electrician
250.30(B)
Wire-Smith
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- United States
i would be more concerned with your primaries. what are you doing with the neutral? i need to refresh my memory but systems with wye primaries can have some serious issues.
http://apps.geindustrial.com/publibrary/checkout/GET-3388B?TNR=White%20Papers|GET-3388B|
are you really wiring them wye-delta?
or are you just saying wye because you have 120/208? but actually wiring it delta
http://apps.geindustrial.com/publibrary/checkout/GET-3388B?TNR=White%20Papers|GET-3388B|
are you really wiring them wye-delta?
or are you just saying wye because you have 120/208? but actually wiring it delta
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we investigated a fatal involving ungroundd delta
common in some mining
bonding of all frames was not in place
a phase faulted to one piece of equipment
a different phase faulted to a different piece of equip in close proximity to the first
the victim came in contact with both while moving thru the tightly packed equip room
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
If i may nit pick a bit....Im not exactly sure what you mean by "wiring it delta". Obviously, generally the winding configuration is fixed and not changeable. Even if it was, changing from wye to delta or vice versa would change the voltage change ratio. I suspect you mean "delta" in the "jargon" sense of three phase conductors with no neutral. A wye delta transformer would be fed with three phases and no neutral. The point on the primary would float. Bad things can happen if the primary neutral is landed or the wye point bonded. Wye wye transformers have some potential issues, as the paper notes.
Wire-Smith
Senior Member
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- United States
you've never seen a three phase transformer that you can configure the primary anyway you want? i know there not as common as they used to be.
and either way i'm still asking him whether it truly is a wye-delta transformer or if he is just calling it that because he is using 120/208 system.
i believe a floating wye primary can come with many problems as well, i need to refresh my memory though.
http://forums.mikeholt.com/showthread.php?t=53682
https://www.eng-tips.com/viewthread.cfm?qid=374777
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Wire-Smith
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- United States
maybe it's not as big a deal as i think since he might be using 3p breakers on primary feeder, what i have heard about using wye primary on is MV distribution that typically use fuses.
electrofelon
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- Cherry Valley NY, Seattle, WA
Well yes, but they are not intended to be changed as the voltage would change and it would be useless..
Wire-Smith
Senior Member
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- United States
i think your looking at what i'm asking different than what i mean by it. i'm asking if it is really wye(configured primary) delta transformer or if he is just calling it wye delta because he has 208.
- Location
- New Jersey
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- Journeyman Electrician
Wire-Smith
Senior Member
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- United States
finally found what i was thinking of
https://www.eng-tips.com/viewthread.cfm?qid=431498
waross (Electrical)25 Oct 17 04:02History, not speculation.
Back one hundred or so years ago, delta:delta transformer banks were the norm.
After WWII when the use of electricity started to increase greatly many utilities gained a cheap and easy 1.73 increase in distribution line capacity by switching the delta:delta systems to wye:delta. The voltage was often increased from 2300 Volts to 4160 Volts.
It was found that the wye:delta bank had some serious issues. Overheating and failing due to circulating crrents, and back-feeding into a fault were two issues. Also a ground fault on one phase of the distribution circuit would be back-fed by the wye:delta bank. This could result in the blowing of one of the fuses on the wye:delta bank.
It was found that these problems could be avoided by floating the primary wye point.
Leaving the wye point floating eliminated the issues with circulating currents, back-feeding and blown fuses.
A new issue arose. Over-voltage transients when the bank was energized.
The solution to this was to connect the wye point to the neutral before energizing the transformer bank. Once the bank was energized, the connection from the wye point to the neutral was opened.
That is why you occasionally see a wye delta bank with an open fused cut-out or a switch to connect the wye point to the neutral.
Closed to energize and then opened and left open.
By the way, I spent over 15 years in a country where the wye:delta connection was popular and I am familiar with most of the issues with wye:delta transformer banks.
Another issue when a residential circuit had one or more wye:delta banks was the frequent failure of residential refrigerators and freezers.
I served as system engineer for a small utility for a number of years. It took about three years to get all of the wye delta banks on our system changed over from wye:delta to wye:wye.
The accepted connection for a wye delta bank is with a floating wye point.
Been there, done that and got the tee shirt.
https://www.eng-tips.com/viewthread.cfm?qid=431498
waross (Electrical)25 Oct 17 04:02History, not speculation.
Back one hundred or so years ago, delta:delta transformer banks were the norm.
After WWII when the use of electricity started to increase greatly many utilities gained a cheap and easy 1.73 increase in distribution line capacity by switching the delta:delta systems to wye:delta. The voltage was often increased from 2300 Volts to 4160 Volts.
It was found that the wye:delta bank had some serious issues. Overheating and failing due to circulating crrents, and back-feeding into a fault were two issues. Also a ground fault on one phase of the distribution circuit would be back-fed by the wye:delta bank. This could result in the blowing of one of the fuses on the wye:delta bank.
It was found that these problems could be avoided by floating the primary wye point.
Leaving the wye point floating eliminated the issues with circulating currents, back-feeding and blown fuses.
A new issue arose. Over-voltage transients when the bank was energized.
The solution to this was to connect the wye point to the neutral before energizing the transformer bank. Once the bank was energized, the connection from the wye point to the neutral was opened.
That is why you occasionally see a wye delta bank with an open fused cut-out or a switch to connect the wye point to the neutral.
Closed to energize and then opened and left open.
By the way, I spent over 15 years in a country where the wye:delta connection was popular and I am familiar with most of the issues with wye:delta transformer banks.
Another issue when a residential circuit had one or more wye:delta banks was the frequent failure of residential refrigerators and freezers.
I served as system engineer for a small utility for a number of years. It took about three years to get all of the wye delta banks on our system changed over from wye:delta to wye:wye.
The accepted connection for a wye delta bank is with a floating wye point.
Been there, done that and got the tee shirt.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
interesting, thank you. I am very interested in transmission and distribution history. I am familiar with the "trick" of changing to wye systems and feeding things L-N instead of L-L to up capacity. That explains why many distribution voltages are multiples of root 3. Although capacity increase may have been the original reason to go wye, I think now it is preferred because in conjuction with MGN, it is a little cheaper. I think also it has to do with our often illogical obsession with grounding.
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