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Joined: Mar 2003
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THERE IS NO NEUTRAL as we know it in a Ungrounded Delta or a Conor phase Grounded Delta! Look it Up. In a Conor Grounded Delta one of the Phase conductors (Is) the grounded conductor.Soares Has plently of Details and Photos of these in there Book Soares Book on Grounding 7th Edition.
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Joined: Mar 2003
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George Is there a Neutral Present (480/277) not being used?? Or is there No Neutral at either source?? If there a Neutral Present Even if its not being used(No load) then all Neutral rules apply EVEN if theres no Load. If there No neutral Period (Straight 480v) then Different as I;ve said in other posts.
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Joined: Jul 2004
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I guess George needs to clarify what this service is. Is the delta grounded? Where is the grounding connection made? If it is corner ground that kicks a couple of other issues, not the least of which is what color is this phase? If there is no grounding at all we wouldn't have the question.
Greg Fretwell
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There is no neutral load. I don't know if the system is a wye or a delta, I don't know if the delta is corner grounded or ungrounded. My guess is that it is corner grounded. But I do know for sure that there is no neutral load and due to the fact that grounding is optional at 480v. We have this issue we are talking about.
George Little
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If this is corner grounded you are switching the neutral, assuming 3 phase transfer equipment. Bond it in the service disconnect on the load side of the TE and you are good to go. You also need to be sure the grounded phase is white.
Greg Fretwell
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Okay Greg- I agree, So what do I do in the transfer switch and what do I do at the generator?
George Little
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I do think it would behoove us as professional code persons to use the term "grounded conductor" for this issue instead of "neutral" since the term "neutral" is not a true code term.
George Little
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You are right about the term "neutral" if this is corner grounded delta. That is the best example of a place where grounded and neutral are not the same thing. Go ahead and bond the "white" at the generator too (if this is really "corner") If it is being switched in 3 pole transfer equipment. You could be using 2 pole equipment tho. Then we are back to worrying about parallel paths.
I would insure that is the same phase we are grounding but the "white" indentification should enforce that.
Greg Fretwell
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George;
To find out what type of incoming (PoCo supplied) Power system you have, check Voltage to Ground at the Service Equipment - or a Panelboard relatively close to the Service Equipment.
First, test Voltage With a "Wiggy": <OL TYPE=A>
[*] Test between Line "A" and Metallic Enclosure of Panel / Gear,
[*] Do the same for Line "B",
[*] Do the same for Line "C" </OL> If any of these L-G tests give a solid reading, the system is Grounded at some point. If the Wiggy acts like it's going to kick in, but quickly stops and shows nothing - on all 3 L-G tests, the system is Ungrounded.
Next, test Voltage with a DVM: <OL TYPE=A>
[*] Test between Line "A" and the Metallic Equipment, as was done in the first tests,
[*] Do the same for Line "B",
[*] Do the same for Line "C" </OL>
If the Wiggy tests showed a Grounded system, see if the DVM's readouts are somewhat equal on all 3 Lines. If they are within 20-25 Volts of each other, the system is a 4 Wire Wye, and the Common Grounded Conductor is carried to the Service Equipment for bonding purposes.
If there is one Line with a noticably higher Voltage than the other two, the system is a Center Tap Grounded Delta. Most likely, the Ground Bonding was done only at the Transformer, but the Conductor from the Center Tap may also be brought to the Service Equipment, then bonded at both the Transformer and the Service Equipment.
I have seen them done both ways for 480VAC 3Ø 3 Wire Grounded Deltas - Grounded only at the Transformer (via center-tapped, center transformer), and with the Conductor brought to the Service Equipment.
If you find that one Line has zero Volts to Ground as read by the Wiggy, and the DVM shows like 10 - 25 Volts from the same Line to Ground, + the remaining two Lines have a high solid reading to Ground; you have a Corner Grounded Delta.
If the Wiggy shows no readings, and the DVM shows really high ones - like 300 - 500 Volts to Ground, you have an Ungrounded Delta. You can verify this by having someone place the Wiggy's leads L-G as you have the DVM's leads L-G, and observe how the Voltage readings on the DVM drop drastically.
If this Project is of a good square footage size, and was built circa 1950 to 1970s, you most likely have an Ungrounded Delta. If there are customers sharing the Transformer which have Commercial Lighting loads, the system may be a 4 wire Wye.
I doubt very much that you will find any 480V Corner Grounded Deltas, but the 480V Grounded Center Tap Delta "Oddball" may test out as would an Ungrounded Delta (most of the time it will not, unless the PoCo's tap and pole mounted grounding electrode conductor have a crappy connection going on!)
Good luck.
Scott35
P.S.: In the above descriptions, with the term "Voltage To Ground" or "Line To Ground", the meaning for "Ground" is to reference Metallic Enclosures - like Switchgear and Panelboards and such; NOT to any Earth Ground or Metallic Water Piping systems.
S.E.T.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
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Scott- Your information is very valid but in my case I was not given that information in the question I was fielding over the phone. I don't have any idea where the job is as it is not in my jurisdiction.
George Little
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HCE727
Delaware County, PA, USA
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