480V, 1PH, 3W (Center Grounded) Feeder

[xptpcrewx]

Is it legal to use a 240V to 480V (center grounded) transformer (fed from a 120/240, 2w system) to supply a single phase feeder? (The 480V side would have ungrounded conductors with 240V to ground). Looking to mitigate voltage drop by stepping up, running, and then stepping down the feeder near the utilization equipment. Thanks in advance.

 

[hillbilly1]

Yes, treat it just like any other transformer installation. Grounding electrodes and all.

 

[xptpcrewx]

Yes, treat it just like any other transformer installation. Grounding electrodes and all.

Assuming it was not center grounded, would it be any different to ground a phase conductor so that ungrounded conductor to ground is 480V?


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[hillbilly1]

It can be, but center tapped is a better route to go, the voltage to ground would be reduced to 240 volts. Doing a 150 amp underground feed that way in the next couple of weeks.

 

[xptpcrewx]

It can be, but center tapped is a better route to go, the voltage to ground would be reduced to 240 volts. Doing a 150 amp underground feed that way in the next couple of weeks.

Can you elaborate how it can be? Please provide code reference. Thanks.


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[LarryFine]

The two-wire feeder has been discussed here before, including a drawing, but I don't know the keywords to do a search.

Why not step up to 600v and back?

 

[mbrooke]

Is it legal to use a 240V to 480V (center grounded) transformer (fed from a 120/240, 2w system) to supply a single phase feeder? (The 480V side would have ungrounded conductors with 240V to ground). Looking to mitigate voltage drop by stepping up, running, and then stepping down the feeder near the utilization equipment. Thanks in advance.

See 450.11 (B)

450.11(B) Transformers. Source Marking.

Here is a PV system inverter output circuit connection to an existing step up transformer. Based on the line diagram, is this a grounded or ungrounded PV system? How can you tell? What color wires should be used or not used for the negative source cuircuit conductors?

www.electricallicenserenewal.com

You might also have much higher inrush than from a factory made step up unit.

 

[xptpcrewx]

See 450.11 (B)

450.11(B) Transformers. Source Marking.

Here is a PV system inverter output circuit connection to an existing step up transformer. Based on the line diagram, is this a grounded or ungrounded PV system? How can you tell? What color wires should be used or not used for the negative source cuircuit conductors?

www.electricallicenserenewal.com

You might also have much higher inrush than from a factory made step up unit.

Good reference. Thank you.


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[mbrooke]

Good reference. Thank you.


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Welcome

IMO it never was in issue for code the require a change

 

[electrofelon]

IMO the step up step down scheme is a horrible solution, but I admit sometimes the only option. You have the cost of the transformers, the losses 24/7 forever, and the poor voltage regulation of two transformers. Many times you are better off just running big aluminum wire. If you are going to do transformers, quit messing around and go up to MV. At the very least go to 600 like Larry said.

 

[ptonsparky]

I did a cost of transformers with primary and secondary fused disconnects vs larger Al wire a few months ago. Larger wire was a hands down winner just with up front costs.

 

[xptpcrewx]

I did a cost of transformers with primary and secondary fused disconnects vs larger Al wire a few months ago. Larger wire was a hands down winner just with up front costs.

I agree it’s may not be the best solution in every application; however, let’s not forget that transformers have the benefit of tap adjustments to overcome voltage drop. Also, if the transformers are supplying 2w systems, the primary OCPD can be used to protect the secondary conductors.


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[xptpcrewx]

IMO the step up step down scheme is a horrible solution, but I admit sometimes the only option. You have the cost of the transformers, the losses 24/7 forever, and the poor voltage regulation of two transformers. Many times you are better off just running big aluminum wire. If you are going to do transformers, quit messing around and go up to MV. At the very least go to 600 like Larry said.

Transformer losses are practically negligible. As far as voltage regulation goes, it’s actually improved vs running a long feeder at the utilization voltage. This is why the utility transmission/distribution systems are not done at the utilization voltage. They take advantage of the larger impedances found with higher voltage systems and the voltage division principle to minimize line losses.

Biggest downside as you’ve mentioned is the cost of two transformers and of course the installation requirements that come with this type of system.


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[texie]

The two-wire feeder has been discussed here before, including a drawing, but I don't know the keywords to do a search.

Why not step up to 600v and back?

As some know ,this is my favorite method. Have to run the numbers for your case to see if this is advantageous or just more wire is the way to go.

 

[xptpcrewx]

As some know ,this is my favorite method. Have to run the numbers for your case to see if this is advantageous or just more wire is the way to go.

Nice diagram. Why don’t you have an EGC ran between structures?


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[hillbilly1]

That set up I’m doing is saving the customer $22,000,the transformer losses in the long run is negligible compared to the savings short term in this particular application.

 

[texie]

Can you elaborate how it can be? Please provide code reference. Thanks.


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Error-see next post.

 

[texie]

Nice diagram. Why don’t you have an EGC ran between structures?


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See 250.30(A)(1) Exception No. 2

 

[xptpcrewx]

See 250.30(A)(1) Exception No. 2

My bad. I didn’t see the note on your drawing. Thanks.


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[ptonsparky]

Nice diagram. Why don’t you have an EGC ran between structures?


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Money saving. Not required but does create additional problems should the grounded conductor fail between the transformers.