Delta to wye conversion

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Stephenup

Member
Location
Beaumont texas
I went to bid a job at a small machine shop and noticed it has a 480 volt delta system with new 480/277 volt wye panels,I called square d and they told me the panel and breakers were not rated for 480 volts to ground ony 277 to ground.I think my best solution will be to convert to 480/277 wye this can be done with a few minor changes and the utility provider will change out the transformers. My question.The motor loads and transformer only see the 480 volts so their should not be any problems with doing this..Now I will check all my boxes motors and transformers to make sure someone did not ground B phase somewhere in the shop.please any commet will be greatly appecerated. Thanks Stephen
 

kwired

Electron manager
Location
NE Nebraska
Is there three or four conductors for service conductors?

Corner ground delta only needs 3 conductors

A grounded wye service will need 4 conductors.


Just something to think about.
 

Stephenup

Member
Location
Beaumont texas
Delta to wye conversion

At the main service their is 4 wire but the nutural is not connect and the power company did not have the 4 wire.It actually looks like it was built for a wye,but the power company made it a delta.Everything their is messed up pretty bad I am a bit concerned getting involved because of liability but it is a very dangerous situation, and needs to be fixed they even have a square d 240/120 QO panel on the 480..The company just bought this business and had a city inspector inspect the building and he passed it ...if that gives you a idea of what I am dealing with..I would just let the job go but someone is going to get hurt if it's not fixed right...by the way this has been like this for a long time the QO panels look several years old.The building about 20 years main service looks original and newer panels inside are a few years old .
 

kwired

Electron manager
Location
NE Nebraska
At the main service their is 4 wire but the nutural is not connect and the power company did not have the 4 wire.It actually looks like it was built for a wye,but the power company made it a delta.Everything their is messed up pretty bad I am a bit concerned getting involved because of liability but it is a very dangerous situation, and needs to be fixed they even have a square d 240/120 QO panel on the 480..The company just bought this business and had a city inspector inspect the building and he passed it ...if that gives you a idea of what I am dealing with..I would just let the job go but someone is going to get hurt if it's not fixed right...by the way this has been like this for a long time the QO panels look several years old.The building about 20 years main service looks original and newer panels inside are a few years old .

Make sure you will get paid for whatever you do.

You can update it for 480/277 wye, or install correct items to use the 480 delta. Most likely if staying with Square D means I-Line panels and appropriate breakers.

QO panels with over 240 volts supplying them need changed regardless of which way you go.

If you change to wye supply and miss an improperly bonded (previously grounded) phase to EGC somewhere in the system - you will figure it out when it blows fuses/breakers:happyyes:
 

big john

Senior Member
Location
Portland, ME
Measure your voltage to ground on each phase, this will give you an idea if you have any hard or soft ground connections.

I would also want to run a 250V megger to ground on this system before I installed the wye.
 

templdl

Senior Member
Location
Wisconsin
I went to bid a job at a small machine shop and noticed it has a 480 volt delta system with new 480/277 volt wye panels,I called square d and they told me the panel and breakers were not rated for 480 volts to ground ony 277 to ground.I think my best solution will be to convert to 480/277 wye this can be done with a few minor changes and the utility provider will change out the transformers. My question.The motor loads and transformer only see the 480 volts so their should not be any problems with doing this..Now I will check all my boxes motors and transformers to make sure someone did not ground B phase somewhere in the shop.please any commet will be greatly appecerated. Thanks Stephen

Instead of guessing as to what it may be what does the nameplate on the transformer say? If it's the POCO's ask them. If it is a Delta, corner grounded or not.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Why not have the utility bring a neutral? You're trying to reinvent the wheel

Sent from my Pixel C using Tapatalk
Because even if the utility brings a neutral the service will be the wrong voltage. If you install an isolation transformer with a wye secondary (PV side) you can use the neutral from it whether POCO supplies a neutral or not. It would be an SDS interconnection.
But our OP cannot do any of those without three phase supply.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
what makes you think the system is inherently dangerous? it has been there all this time and not killed anyone.

it is not upto code and some parts are operating outside of their ratings but most of this stuff is pretty conservatively rated, so I suspect there is no immediate danger.

I am not saying you should not suggest the owner pay to fix it, but the reality is that it has been working like this for a long time and apparently not harmed anyone.

Best bet IMO is to get the POCO to bring in 480/277 instead of 380 delta and go from there.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Because even if the utility brings a neutral the service will be the wrong voltage. If you install an isolation transformer with a wye secondary (PV side) you can use the neutral from it whether POCO supplies a neutral or not. It would be an SDS interconnection.
But our OP cannot do any of those without three phase supply.
Oops. Wrong thread. Sorry. But leaving out the PV part, you can give the secondary neutral without a primary neutral. So as long as voltage transformation is necessary...
 

kwired

Electron manager
Location
NE Nebraska
Why not have the utility bring a neutral? You're trying to reinvent the wheel

Sent from my Pixel C using Tapatalk
Not that simple. If existing is corner grounded or ungrounded delta - there is no neutral to bring in.

If it is a high leg delta - there already is a neutral and should be installed and functioning.

Neither case makes a 277/480 volt rated breaker acceptable other then the high leg system (which will be about 416 volts on high leg of this system) can use 277/480 breakers on A and C phases - but still leaves B phase unusable in something like a Square D NF series panel because there are no straight 480 volt breakers made for that series.

The mentioned QO panel on the 480 volt system is wrong period as those breakers are only 240 volts max.
 
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