Transformer on 3 phase delta with high leg

[hockeyoligist2]

I'm not real familiar with 3 phase with a high leg 208/120. The transformer that we are putting in (240 to 120/240) doesn't have a grounding terminal. Should I just bond back to the main (drill a hole in the casing and put on a ground lug)? And there will be ground fault recepticles used on this transformer will they work properly?

 

[infinity]

So if I understand you correctly, you're installing a 120/240, 3 phase, 4 wire delta secondary transformer?

 

[hockeyoligist2]

yes, it is fed by 208/120 we connected the 2- 120's to the primary, secondary is 120/240. No XO terminal no ground lug, actually no lugs at all just x-1 x-2 x-3 x-4 wires etc. (cutler hammer) then . hmmmm i forgot the secondary wire terminals, but it doesn't have any ground only a common and 2 120's for 120 or 240. It is fed by a 4 wire delta 120, 208, 120 and it has a ground wire from the poco. As I said before i'm not familiar with this I'm used to 3 phase 480 and higher.

 

[Smart $]

I'm thoroughly confused. It's sounds as though your service (or the supply) is 240VAC, 3?, 4W. ...which means btw you already have 240/120VAC, 1?, 3W (you just do not use the high leg, i.e the 208V one)... and you are trying to add another transformer that has two secondary windings which can be configured for 240 VAC, 1? primary to 240/120VAC, 1?, 3W or a straight 120VAC output. The X terminals, or in this case "wires" are the secondary connections. As I recall off the top of my head, X1 and X2 are one winding, X3 and X4 are the other. To get 240/120 out, X1 and X4 are your hots and X2 and X3 are connected as the neutral and get bonded to ground. For straight 120, X1 and X3 are connected together, as are X2 and X4. IIRC, the X2-X4 gets bonded to ground as your neutral. The primary should be H1 and H2...

[EDIT ADD]You should verify the winding markings and not connect by what I wrote. After pondering what I wrote, there's a good chance X2 and X3 are the other way... X1 and X3 the terminations for one winding, X2 and X4 the other.[END EDIT]

Anyway, the only purpose I can see offhand for doing this is to achieve perhaps some sort of load balancing on the supply (using A-B or B-C for the primary), or perhaps as a means of isolation...???

As for grounding, you'll have to provide your own means. I have to do the same to a 400KVA transformer on my current project. It's hard to believe a grounding terminal wasn't provided. On top of that, I have two 1/0 EGC's coming in on the supply side and six 1/0 EGC's going out on the load side!!!

 

[hockeyoligist2]

I'm thoroughly confused. It's sounds as though your service (or the supply) is 240VAC, 3?, 4W. ...which means btw you already have 240/120VAC, 1?, 3W (you just do not use the high leg, i.e the 208V one)... and you are trying to add another transformer that has two secondary windings which can be configured for 240 VAC, 1? primary to 240/120VAC, 1?, 3W or a straight 120VAC output. The X terminals, or in this case "wires" are the secondary connections. As I recall off the top of my head, X1 and X2 are one winding, X3 and X4 are the other. To get 240/120 out, X1 and X4 are your hots and X2 and X3 are connected as the neutral and get bonded to ground. For straight 120, X1 and X3 are connected together, as are X2 and X4. IIRC, the X2-X4 gets bonded to ground as your neutral. The primary should be H1 and H2...

As for grounding, you'll have to provide your own means. I have to do the same to a 400KVA transformer on my current project. It's hard to believe a grounding terminal wasn't provided. On top of that, I have two 1/0 EGC's coming in on the supply side and six 1/0 EGC's going out on the load side!!!

The reason for the transformer is POCO says there is no neutral (grounded conductor) only a ground. The primary is hooked up 240, from the 120 legs, I'm not having a problem with how it's wired that is pretty straight forward on the diagram. I'm just concerned about the ground fault recepticles working as they should. I went ahead and drilled a hole for a ground lug in the case. Should I ground the X-2 and X-3 so that the recepticales will work? I guess I'll just wait till POCO turns on the power then test them.


Thanks

 

[Smart $]

The reason for the transformer is POCO says there is no neutral (grounded conductor) only a ground. The primary is hooked up 240, from the 120 legs, I'm not having a problem with how it's wired that is pretty straight forward on the diagram. I'm just concerned about the ground fault recepticles working as they should. I went ahead and drilled a hole for a ground lug in the case. Should I ground the X-2 and X-3 so that the recepticales will work? I guess I'll just wait till POCO turns on the power then test them.


Thanks

I said I was, "...thoroughly confused." You wrote, "It is fed by a 4 wire delta 120, 208, 120 and it has a ground wire from the poco." To me that is 240/120V, 3?, 4W PLUS a ground wire. There is no such thing as a high leg (what you are calling 208) unless a mid-tap on the poco transformer is grounded... and that becomes the grounded conductor, otherwise known as the neutral. Oh well!!!

Anyway, I would bond X2-X3 to ground, either in the transformer or in the main disconnect/panel on the secondary side, whichever is easier, but not both. Generally, I do it at the disconnecting means as I assume it to be most likely the first place anyone would look to verify a grounded system. FWIW, the GFCI's would work regardless, but a GFCI receptacle tester may not trip the device, whereas the built-in TEST button would.

 

[sandsnow]

XFMR's are typically furnished with no lugs including ground lugs. It is up to you to install the correct number and size of lugs in the proper places.

You need to scrape the paint and bolt lugs to the enclosure.

You state the xfmr has a hi-leg. So you are going 240 3 phase wire to 120/240 3phase 4wire. Forget about including 120 and 208 in the descrioption of your transformer. Although those voltages are present, they are not used in the description of the xfmr. You are installing this xfmr because the POCO is not supplying you a grounded conductor. I am suprised they are giving you a grounding conductor. Just not done in most places.

Here's the set up.

X1 - X2 - X3 are the three points of your delta triangle. X4 is midway between X1 and X3. X4 is your grounded conductor point. X4 is bonded to the case. The wire from your grounding electrode connects to X4.

Voltage is 240 between any two combinations of X1 - X2 -X3. From X2 to X4 you will read 208V.

Maybe someone can post a schematic of this xfmr.

GFCI devices will work fine.

 

[sandsnow]

I said I was, "...thoroughly confused." You wrote, "It is fed by a 4 wire delta 120, 208, 120 and it has a ground wire from the poco." To me that is 240/120V, 3?, 4W PLUS a ground wire. There is no such thing as a high leg (what you are calling 208) unless a mid-tap on the poco transformer is grounded... and that becomes the grounded conductor, otherwise known as the neutral. Oh well!!!

Anyway, I would bond X2-X3 to ground, either in the transformer or in the main disconnect/panel on the secondary side, whichever is easier, but not both. Generally, I do it at the disconnecting means as I assume it to be most likely the first place anyone would look to verify a grounded system. FWIW, the GFCI's would work regardless, but a GFCI receptacle tester may not trip the device, whereas the built-in TEST button would.

Wait, I thought he said it was 3 phase?? Tying X2 and X3 together is done in a single phases xfmr.

 

[hockeyoligist2]

Sorry to be so confusing, I'm not used to dealing with the 208 stuff. POCO hooked up the power this morning, with the tester it didn't trip but it does trip with the built in.

Thanks for all the help !!!!