480 to 240 volt transformer

[peter d]

I have a situation where I'm connecting a machine that is 230 volts, 3 phase. I'm using a 480 to 240 volt, delta/delta transformer to obtain this voltage. I'm thinking that I need to corner ground the secondary. What say you?


Now, as why I'm connecting a 230 volt machine with 480 volts available, a mistake was made in the ordering of said machine and it can't be corrected at this point. :roll:

 

[electrofelon]

I have a situation where I'm connecting a machine that is 230 volts, 3 phase. I'm using a 480 to 240 volt, delta/delta transformer to obtain this voltage. I'm thinking that I need to corner ground the secondary. What say you?


Now, as why I'm connecting a 230 volt machine with 480 volts available, a mistake was made in the ordering of said machine and it can't be corrected at this point. :roll:

I would say that you either have to corner ground, or you may run it ungrounded with ground detectors. If it has a center tapped winding then you would have to ground it.

 

[peter d]

I would say that you either have to corner ground, or you may run it ungrounded with ground detectors. If it has a center tapped winding then you would have to ground it.

It does have a center tap, but the neutral is not needed. Running it ungrounded is out of the question.

 

[curt swartz]

If the 240V side had a center tap why not ground it there instead of corner grounding it?

 

[peter d]

If the 240V side had a center tap why not ground it there instead of corner grounding it?

I thought about doing that, just thought that it was six of one, a half dozen of the other as far as where I grounded it.

 

[electrofelon]

I thought about doing that, just thought that it was six of one, a half dozen of the other as far as where I grounded it.

Ok I concede if you are not using the center tap as a circuit conductor then I agree you do not have to ground it. I think that is the way to go though. A corner grounded system is quite confusing/ an oddball for many "electricians" and the equipment may be more of a hassle to get.

 

[peter d]

Ok I concede if you are not using the center tap as a circuit conductor then I agree you do not have to ground it. I think that is the way to go though. A corner grounded system is quite confusing/ an oddball for many "electricians" and the equipment may be more of a hassle to get.

I think for simplicity's sake I will use the center tap. At least then the voltage readings phase to phase will make sense to these "electricians" you speak of.

 

[templdl]

I have a situation where I'm connecting a machine that is 230 volts, 3 phase. I'm using a 480 to 240 volt, delta/delta transformer to obtain this voltage. I'm thinking that I need to corner ground the secondary. What say you?


Now, as why I'm connecting a 230 volt machine with 480 volts available, a mistake was made in the ordering of said machine and it can't be corrected at this point. :roll:

Is the name plate show 240/120v which would indicate a delta secondary with a lighting tap? Loop
Attaching a picture of the nameplate of the transformer would be very helpfull in order to not misinterpreted your application. There could even be an outside chance that it may even be drive transformeras such transformers commonly have a wye secondary with a 240y/139 volts where the X0 is grounded.
But if it is in fact a 240 delta if there isn't an application reason not to ground it I would just corner ground it.

 

[peter d]

Attaching a picture of the nameplate of the transformer would be very helpfull in order to not misinterpreted your application. There could even be an outside chance that it may even be drive transformeras such transformers commonly have a wye secondary with a 240y/139 volts where the X0 is grounded.
But if it is in fact a 240 delta if there isn't an application reason not to ground it I would just corner ground it.

I didn't take a picture of the data plate but it is definitely a delta/delta.

 

[templdl]

I didn't take a picture of the data plate but it is definitely a delta/delta.

A 240/120 delta w/ a lighting tasp may be more commonly available for a transformer with a delta secondary but from what I can tell you have stated that has a basic 240 delta secondary.

 

[augie47]

It might pay you to run the quotation by the manufacturer. Some equipment, especially with drives, does not like grounded delta systems so you may need to stick with ungrounded and detectors.

 

[kwired]

It might pay you to run the quotation by the manufacturer. Some equipment, especially with drives, does not like grounded delta systems so you may need to stick with ungrounded and detectors.

Those same drives that don't like corner ground, may not like a high leg or an ungrounded supply either.

The surge protectors on the drive input is often the issue, they are connected from each input lead to grounded chassis, and the clamping voltage level is the key into what source may not be acceptable.

 

[templdl]

Those same drives that don't like corner ground, may not like a high leg or an ungrounded supply either.

The surge protectors on the drive input is often the issue, they are connected from each input lead to grounded chassis, and the clamping voltage level is the key into what source may not be acceptable.

Thus drive isolation transformers are commonly used which have wye secondaries where the neural is grounded.

 

[peter d]

It might pay you to run the quotation by the manufacturer. Some equipment, especially with drives, does not like grounded delta systems so you may need to stick with ungrounded and detectors.

I don't see that happening, I just need to get this up and running. I have decided to ground the center tap and be done with it.

 

[templdl]

I don't see that happening, I just need to get this up and running. I have decided to ground the center tap and be done with it.

Thern the transformer isn't a basic delta secondary but a 240/120 delta with a lighting top then.

 

[peter d]

Thern the transformer isn't a basic delta secondary but a 240/120 delta with a lighting top then.

Yes, it is. My fault for not mentioning it, but I didn't see how that mattered as far as where to ground it since it's only serving one dedicated load.

 

[templdl]

Yes, it is. My fault for not mentioning it, but I didn't see how that mattered as far as where to ground it since it's only serving one dedicated load.

Yes, thanks for your reply. One of the things that I attempt to do when addressing an application question which may at times seem to be unreasonable is to assure that we are on the same page and that there are no assumptions.
Instead of corner grounding a delta where you would have 240v to ground between the two ungrounded phases and ground you would end up with 208v to ground from the 'B' phase and ground and 120v to ground from the 'A'and 'C' phases which I would prefer.

 

[iwire]

It does have a center tap, but the neutral is not needed. Running it ungrounded is out of the question.

If the 240V side had a center tap why not ground it there instead of corner grounding it?

I am no pro with these systems but I think you would have to ground the center tap per 250.20(B)(1).

250.20 Alternating-Current Systems to Be Grounded.


(B) Alternating-Current Systems of 50 Volts to 1000 Volts.
Alternating-current systems of 50 volts to less than 1000 volts
that supply premises wiring and premises wiring systems shall
be grounded under any of the following conditions:

(1) Where the system can be grounded so that the maximum
voltage to ground on the ungrounded conductors
does not exceed 150 volts

(2) Where the system is 3-phase, 4-wire, wye connected in
which the neutral conductor is used as a circuit conductor

(3) Where the system is 3-phase, 4-wire, delta connected in
which the midpoint of one phase winding is used as a
circuit conductor

But I could be wrong.

 

[GoldDigger]

I am no pro with these systems but I think you would have to ground the center tap per 250.20(B)(1).



But I could be wrong.

I think that you are not giving enough weight to the "if *used* as a circuit conductor" part.
If the center tap is there but not used by any loads, then it does not, IMHO, need to be grounded.

 

[iwire]

I think that you are not giving enough weight to the "if *used* as a circuit conductor" part.
If the center tap is there but not used by any loads, then it does not, IMHO, need to be grounded.

Where are you finding 'if used' in the sections I quoted?