Three phase equipment Single phase power v

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Finite10

Senior Member
Location
Great NW
I don't know why not. We do that for feeders all the time.

The AHJ could maybe hit you with 110.12, so a call before might ease your mind. Did you get a good deal or just using something you have?
 

kwired

Electron manager
Location
NE Nebraska
For typical miniature frame breaker panels you will have every third space unavailable for use. For larger frame like I-Line you order breakers with bus connectors for appropriate buses and all breaker space is available for use.
 

dxco

Member
Maybe!

Maybe!

Yes, make sure the voltage matches. You don't want to fry your toaster with 277 volts, do you???
If you're unsure, consult an electrician!

DXinDSM
 

natfuelbill

Senior Member
The existing installation was installed by others. A three phase service 480v 200a to a three wire feeder (no EGC no grounded conductor no metal conduit) to a 480 to 208/120 step down xfrmr. One primary coil went to ground. I want to re-purpose one of the phase wires as a EGC and install a 480 to 120v single phase xfrmr.
Feed the three phase panel with 120/208v.
 

Smart $

Esteemed Member
Location
Ohio
The existing installation was installed by others. A three phase service 480v 200a to a three wire feeder (no EGC no grounded conductor no metal conduit) to a 480 to 208/120 step down xfrmr. One primary coil went to ground. I want to re-purpose one of the phase wires as a EGC and install a 480 to 120v single phase xfrmr.
Feed the three phase panel with 120/208v.
If existing, have you determined the load on the 208/120 panel? Can you flop all the third phase over to single phase? Are there any 4-wire circuits? Have you looked into making the service corner grounded?

My personal opinion is that you are proposing a hack fix :roll:
 

natfuelbill

Senior Member
The loads are all 120v. Consisting of electronics and lights. The three phase was for an air compressor that has been removed.

Corner grounded has not been considered. Can you explain?
 

kwired

Electron manager
Location
NE Nebraska
The existing installation was installed by others. A three phase service 480v 200a to a three wire feeder (no EGC no grounded conductor no metal conduit) to a 480 to 208/120 step down xfrmr. One primary coil went to ground. I want to re-purpose one of the phase wires as a EGC and install a 480 to 120v single phase xfrmr.
Feed the three phase panel with 120/208v.

you will have 1.73 times more power available if you leave it as it is and it will not cost anything either. Assuming same KVA transformer. Why would you want to make these changes?

I see there was no grounded conductor, is it a long run? Can you move the transformer to the load end? would still need an egc though.
 

Smart $

Esteemed Member
Location
Ohio
The loads are all 120v. Consisting of electronics and lights. The three phase was for an air compressor that has been removed.
Are there any shared neutral conductors, especially on the circuits that are connected to the third Line?

And you did not answer about the [calculated] load on the 208/120 panel... Your existing load will be the same but apportioned to two feeder conductors and two line buses in the panel, rather than three... possibly exceeding the feeder and panel's rating.

Do you plan to re-feed with 120/208 or 120/240? Are any 480 3? 3-wire to 120/208 1? 3-wire xfmrs even marketed? Using 120/208, the neutral feeder conductor and panel's neutral bus will see current equal to that of the line conductors and buses.

Corner grounded has not been considered. Can you explain?
One of the 480V 3? conductors is grounded. Did anyone even check to see if it is already grounded? Is there a ground detector on the system? Or is the service 480/277? You did not say what the service actually is... only that the feeder was ungrounded... but are you certain of this?

The real Deficiency is the missing EGC in the primary feeder.
From a safety standpoint, yes... but if the service really is ungrounded, an EGC would not serve any purpose if there is no ground detector.
 

Smart $

Esteemed Member
Location
Ohio
you will have 1.73 times more power available if you leave it as it is and it will not cost anything either. Assuming same KVA transformer. Why would you want to make these changes? ...
He's lost 1/3 of the existing xfmr's kVA rating. How would this be 1.73 times more power than a fully-functioning, same-kVA-rated replacement xfmr? :confused:
 

Smart $

Esteemed Member
Location
Ohio
...a three wire feeder (no EGC no grounded conductor no metal conduit)...
Just exactly what is there? Cable or wire in conduit? What type of conduit? Exposed subject to damage or not, or concealed, underslab/underground and not not subject to damage? ...
 

natfuelbill

Senior Member
Like i said this is what I found
Service is 480/277 3 phase 4 wire
Main is 200A fused 3 phase 480v rated
Feeder is 3-#4/0 in buried PVC conduit 1200' long.
Transformer is 45 kva 480 pri 208/120 sec
480 v three phase disconnect tied off tranny primary. Was for a removed air compressor.
Tranny feeds a 208/120v 200a main breaker panel.
There are only 5 120v 1p 15a branch breakers in a three phase panel.
Total load is 3000 watts only!

I am thinking of using the existing main disconnect with only two fuses.
Repurpose one of the phase conductors to be an EGC.
Replace tranny with 480 to 120/208 single phase tranny.
Replace secondary panelboad with single phase.
 

Smart $

Esteemed Member
Location
Ohio
Like i said this is what I found
Service is 480/277 3 phase 4 wire
Main is 200A fused 3 phase 480v rated
Feeder is 3-#4/0 in buried PVC conduit 1200' long.
Transformer is 45 kva 480 pri 208/120 sec
480 v three phase disconnect tied off tranny primary. Was for a removed air compressor.
Tranny feeds a 208/120v 200a main breaker panel.
There are only 5 120v 1p 15a branch breakers in a three phase panel.
Total load is 3000 watts only!

I am thinking of using the existing main disconnect with only two fuses.
Repurpose one of the phase conductors to be an EGC.
Replace tranny with 480 to 120/208 single phase tranny.
Replace secondary panelboad with single phase.
If this were on MY property, I'd probably consider just isolating the faulty winding pair and flop the respective line branch circuits over to one of the other two functional lines... and consider alternatives later.

But not being my property, I cannot completely dismiss your fix as a hack now that I better understand the details.

But I am still wondering just where you plan to get a 120/208 1? xfmr...??? FWIW, you already have one... :roll::roll::roll:
 
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Smart $

Esteemed Member
Location
Ohio
...

But I am still wondering just where you plan to get a 120/208 1? xfmr...??? FWIW, you already have one... :roll::roll::roll:
PS: Do you realize that if you should find a 120/208 1? xfmr, you will not be able to retask one conductor as an EGC. A 120/208 secondary would require a 3? primary.

If you are going 1?, the xfmr will need to be 480 to 120/240...
 

kwired

Electron manager
Location
NE Nebraska
He's lost 1/3 of the existing xfmr's kVA rating. How would this be 1.73 times more power than a fully-functioning, same-kVA-rated replacement xfmr? :confused:


I had some kind of brain cramp. I guess what I had on my mind was that you would have 1.73 times more power for a three phase system than you have for a single phase of same voltage and amperage capacity, then I took it too far mentioning same kva of transformer.

OP has made it a little more clear why he wants to do what he wants to do. It may seem a little unconventional but it will work.
 

natfuelbill

Senior Member
One more question.

Say the tranny is to remain three phase, and the three phase conductors remain as phase conductors.
Can an EGC be added to the circuit by burying it? Ie NOT installed in the same PVC conduit as the phase conductors?
 

iwire

Moderator
Staff member
Location
Massachusetts
Say the tranny is to remain three phase, and the three phase conductors remain as phase conductors.
Can an EGC be added to the circuit by burying it? Ie NOT installed in the same PVC conduit as the phase conductors?

No, 300.3(B) requires that the EGC be run with the circuit conductors.
 
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