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Discussion Starter · #1 · (Edited)
Does anyone have a diagram to describe how to hook this up properly as far as grounding . There will be a fused disconnect on the secondary that I am concerned about using a corner ground on
 

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If you only have 480V loads then use the corner ground method. Or if you have a method of ground fault detection you can leave it ungrounded but be sure to run a bond.


You would still have 3 phases it just in reference to ground 2 legs would be 480v and 1 would be 0v
 

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Discussion Starter · #3 ·
Awesome thanks for the picture. It is only one 480 load so the corner ground sounds like my route. By grounding one phase does that just direct fault current from the other phases to ground? With the corner grounded would it be a line to line fault in away if one of the others phases was to contact bare metal?
 

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Discussion Starter · #4 ·


This is an extremely poor drawing I made on my iPad but is this how it would be connected using the ground from the service disconnect and bringing that into the transformer or would I just bring a ground in from the panel I am feeding this with?
 

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Awesome thanks for the picture. It is only one 480 load so the corner ground sounds like my route. By grounding one phase does that just direct fault current from the other phases to ground? With the corner grounded would it be a line to line fault in away if one of the others phases was to contact bare metal?
It would be a line to line fault in theory. Any fault on the other 2 non grounded phases would do that. Another possibility is running the system ungrounded and using a ground detector to detect faults but unless service continuity is a requirement you don't have too.


Is this an existing transformer?
 

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View attachment 33585

This is an extremely poor drawing I made on my iPad but is this how it would be connected using the ground from the service disconnect and bringing that into the transformer or would I just bring a ground in from the panel I am feeding this with?
This drawing is WRONG completly different transformer shown.

On the primary/Input side/X/low voltage side you do not need to pull a neutral.
 

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Do not connect to X0. Run your 208 to X1, X2, X3. Connect you disconnect for your machine to H1, H2, H3. Run your ground from the supply (208) to the xfmr frame, H1 then into the disconnect. Put a dummy fuse in the grounded phase. Put a label on the disconnect "480 Volts" "Corner Ground".

One time I had to get 480 from 240. I ordered a transformer, 240 to 277/480. I did not want a corner ground so the service technicians would not be dumbfounded by the input voltages.
 

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Discussion Starter · #8 ·
Thanks for all the info so far guys the plan is to use this for a motor load is that a bad idea using this in reverse with a motor? I read that the input current can be 8 to 9 times the rated amps for a very short period of time would that be happening everytime the motor is started?
 

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Thanks for all the info so far guys the plan is to use this for a motor load is that a bad idea using this in reverse with a motor? I read that the input current can be 8 to 9 times the rated amps for a very short period of time would that be happening everytime the motor is started?
My concern is also the magnetizing inrush. I am not an expert on dry transformers but I do know that when reverse fed the magnetizing inrush might be greater than normal since engineering specs aren't around back feeding. You can certainly try though.
 

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Thanks for all the info so far guys the plan is to use this for a motor load is that a bad idea using this in reverse with a motor? I read that the input current can be 8 to 9 times the rated amps for a very short period of time would that be happening everytime the motor is started?
The biggest issue I've seen is when you initially energize the transformer, the inrush current is much higher than on a traditionally connected one. You'll need to make sure the inrush current rating is high enough if you feed it with a breaker. If it's fused, it will probably be okay. The biggest issue is that these transformers are readily available and reasonably priced. A transformer designed for 208 - 480 is very spendy.
 

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Sometimes I will get a 6 hole terminal bar and drill and tap 2 1/4-20 holes in the bottom between the wire holes. Drill matching holes in the bottom of the transformer housing. Route your incoming ground, outgoing ground, building steel, neutral bond (H2 in this case) wires to this terminal strip.
 

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Sometimes I will get a 6 hole terminal bar and drill and tap 2 1/4-20 holes in the bottom between the wire holes. Drill matching holes in the bottom of the transformer housing. Route your incoming ground, outgoing ground, building steel, neutral bond (H2 in this case) wires to this terminal strip.
It is not a neutral it is a grounded conductor big difference in this application.
 

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Discussion Starter · #19 ·


So to clarify my main system ground that bonds my original system neutral needs to be hooked up to H2 on the transformer ? Now do I also use this ground as my bond for the transformer case aswell as carry on as my bond for my new system?
 

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The last corner ground I saw was back in 1980's. Later it was changed to 277/480. This was a grain elevator. Also had 3 greens going to a motor on top.

Answer to above yes. Also H1, H2 & H3 are all the same size conductor. Just that one is at zero potential to earth.
 
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