Transformer Question

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brian john said:
SMART:

Not necessarily, if this is a buck boost, the XO and HO are common and therfore tihs is not a SDS.
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I assume you are talking the originating system X0, as he said there was no xfmr X0.

You are correct if one wants the derived system to not be "separately" derived. Simply connect the 208 system neutral to 480/277V secondary neutral (H0). Still, with this connection to H0, no ground detector needed.

In either case, buck-boost is not the appropriate term for the setup. It will either be a derived system or a separately derived system. For a derived system, the primary feeder will consist of L1, L2, L3, N, and EGC. There will not be an SBJ. For a separately derived system, the primary feeder will consist of L1, L2, L3, and EGC, and an GEC (the GEC and EGC can be possibly one appropriately-sized and connected conductor) then an SBJ.
 
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Sorry I missed where he said NO XO....As noted bond HO and the system is (or should ) be operational and NEC compliant.
 
radiopet said:
So you are saying the HO represents the Corner Ground Delta on the secondary .
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No. The output of the xfmr is wye configured. H0 is the neutral connection... even if it is not used. When H0 is bonded to ground, all lines (H1, H2, H3) will have voltage to ground... so no ground detector is necessary.
 
Smart $ said:
No. The output of the xfmr is wye configured. H0 is the neutral connection... even if it is not used. When H0 is bonded to ground, all lines (H1, H2, H3) will have voltage to ground... so no ground detector is necessary.
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Im telling ya man...its output is 480V Delta , not Wye...honestly
 
radiopet said:
Im telling ya man...its output is 480V Delta , not Wye...honestly
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I'm telling you man if the 480V side has H1, H2, H3, Ho - It's a Wye on the 480V side. The Ho may not be hooked up, but it is still a wye

If 208 side does not have an Xo, it's a delta.

Unless it's an auto transformer --

Can you get a model number from the name plate. We could look it up and see just what it is. We really should stop guessing.

carl
 
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Regarding the existing transformer connections,
is it:
a) X1, X2, X3, X0 and H1, H2, and H3
or
b) X1, X2, X3 and H1 , H2, H3 and H0
 
radiopet said:
Im telling ya man...its output is 480V Delta , not Wye...honestly
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Paul, they're saying that only a Y configuration has an H-0 or an X-0 terminal; nobody re-labels a grounded corner as an -0 terminal.

If there's an H-0 or an X-0, whether grounded or not, it's a Y primary or secondary. Delta terminals are always labeled 1, 2, and 3.
 
Last week I had a transformer with 2 XO's and no H1, simple fix, little bit of Magic Marker...Manufacutre screw up.
 
brian john said:
Last week I had a transformer with 2 XO's and no H1, simple fix, little bit of Magic Marker...Manufacutre screw up.
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That would have an apprentice scratching his head for a good while, trying to hook that thing up. On second thought, not many electricians let apprentices terminate transformers anyhow.
 
1) I agree with those above who say we are doing lots of guessing. radiopet, it sounds like you are not 'on site' and are reporting what someone else is telling you. Maybe they could send a picture of the transformer nameplate; that would clear up lots of confusion.

2) Question for those who know terminal naming conventions: if the transformer has a 'high leg delta' secondary with a center tap in the center of one of the delta legs, what would that center tap terminal be named?

3) Normally ungrounded systems are used to provide 'continuity of service'; if you have a _single_ ground fault it won't cause much current flow, and no OCPD will trip. This is why ground fault detectors are required with ungrounded systems; you detect the ground fault, someone notices the light, you schedule downtime, and fix the problem. It is entirely possible to rig your ground fault detector to do something else, such trigger a shunt trip on a breaker; but if a ground fault will cause a breaker to trip, then you clearly don't need continuity of service!

-Jon
 
LarryFine said:
Paul, they're saying that only a Y configuration has an H-0 or an X-0 terminal; nobody re-labels a grounded corner as an -0 terminal.

If there's an H-0 or an X-0, whether grounded or not, it's a Y primary or secondary. Delta terminals are always labeled 1, 2, and 3.
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Thanks guys....It is indeed a wye primary but the caller insisted it was a 480 v secondary delta...as he said he has (2) in the room and one is working right now to one of the elevators. I also asked im what was his system voltage and he said it was 208....and thats why the elevator provider supplied the transformers...they needed a 480V delta secondary.....I will look him up and see if he can provide a picture....but i am fairly certain the guy knows what he is dealing with.....he is just trying to figure out what the HO is for on the secondary....maybe it is for 277....anyway it does only have X1,X2,X3 and HO,H1,H2,H3 and he has the Brown,Orange,Yellow to the elevator from the secondary H1,H2,H3 terminals.

I will see if I can get him to snap a picture . Thanks Guys.....I was doing the same guessing trying to help the guy...but in the way he had it I atleast wanted him to add some detection for the maintenance crew.
 
winnie said:
...

2) Question for those who know terminal naming conventions: if the transformer has a 'high leg delta' secondary with a center tap in the center of one of the delta legs, what would that center tap terminal be named?

...
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X4 :)
 
radiopet said:
...they needed a 480V delta secondary...
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Most utilization equipment cannot tell the difference between 480VAC 3? 3W supplied by a delta or wye configured xfmr secondary. I'm assuming the caller is telling you the equipment needs a 480 delta supply simply because it has no N terminal... but the 480VAC 3? 3W supply system can be either delta or wye.
 
radiopet said:
Thanks guys....It is indeed a wye primary...
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From what you told us it is not a wye primary... it is a Delta primary being supplied from a 208Y/120 system. The absence of an X0 terminal does not confirm it is a delta primary, but back in your post #16 you said, "He said the diagram on the front of the unit shows a Delta/Wye symbols and he has 208V coming in and 480V going out to feed the elevator." This tells me (with some assumption) that the Delta symbol is on the left (primary) and the Wye symbol is on the right (secondary).
 
X4 would be the center-tap coil (or I guess in this transformer's notation, if it were delta, H4).

I think Smart $ has it correct. It appears to be a delta primary (208 volt like he said, and no X0 terminal) and wye seconday (480 volt).

Now if we can get the nameplate picture to see if Smart $ wins the free vacation, all will be settled.
 
If in fact the transformer terminals are marked X1-X2-X3 then it is a 208 delta primary and H1-H2-H3-H0 is a 480v 'Y' with the H0 being the neutral.
There is no "high leg."

From the 208Y/120 supply bring out the L1, L2, and L3 and an EGC terminating them on the X1, X2, and X3 and the egc bond to the transformer enclosure.
The H0 should be simply grounded per NEC requirements and the H1, H2, and H3 are brought out as L1, L2, and L3 with an EGC that is connected to the grounded H0. No neutral conductor is required if there are no line to neutral loads.

I just provided (2) 225kva encapsulated transformers that were 480D-4160Y/2400 to replace some 4160D-480Y/277 thate were being used as step up transformers. Trying to ground the 4160 was a bid issue which left only one choice but to replace the transformers.
 
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