277 to Nutral needed

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Toros

Senior Member
Location
Tujunga, CA
Hi
I have the existing 1200A service @ 480v, 3-wire
now the new lighting load that requires 277V input are waiting for my decision

What type dry xfrmer do I need????

I am thinking ,
480v , 3-wire 3ph. as primary
480/277v , 4-wire, 3ph. as secondary
(And used only "H" & "0" terminals of primary side for supplying the loads,
not using secondary terminals) ???????

Thank you
 

Toros

Senior Member
Location
Tujunga, CA
277v Nuetral needed

277v Nuetral needed

Hi
instead of using a transxfrmer, can I get 277 neutral from the system grounding of existing 480v, 3-wire (that has no nuetral)
to supply 277v lighting loads ??????


Thanks
 

victor.cherkashi

Senior Member
Location
NYC, NY
Electrical power is close loop, if current come out from one transformer (system) it cannot go other system. The question is not clear

Sent from my Nexus 5 using Tapatalk
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Hi
instead of using a transxfrmer, can I get 277 neutral from the system grounding of existing 480v, 3-wire (that has no nuetral)
to supply 277v lighting loads ??????


Thanks
If I understand your question the answer is no. It would be the same as a 120V/240V system. You would be putting unwanted current on the EGC of the system if you use the EGC as a neutral.
 

mach531

Member
Location
Buffalo, NY
I've had a similar application before. We used a dry type, indoor, isolation transformer like you suggested (480V delta primary - 480/277 wye secondary) but your load would be connected to secondary terminals (X1, X2, X3) including your neutral on X0. Presuming you ground X0 of course.

It's just like a step down transformer except your phase-phase voltage ratio is 1:1.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Hi
I have the existing 1200A service @ 480v, 3-wire
now the new lighting load that requires 277V input are waiting for my decision

What type dry xfrmer do I need????

I am thinking ,
480v , 3-wire 3ph. as primary
480/277v , 4-wire, 3ph. as secondary
(And used only "H" & "0" terminals of primary side for supplying the loads,
not using secondary terminals) ???????

Thank you
If I understand it, you have 480V delta at present and need some amount of 277V to run some new lights on.

If you only need a moderate amount of 277V, you can get a single phase transformer 480 to 277V.

If you need more than what is appropriate for a single phase xfmr, you can get a 3 phase 480 D to 480 Wye transformer.

In either case, you will be creating a separately distributed system and need to be aware of the requirements for such a system and will be feeding the new 277V loads off the load (secondary) side of the xfmr.

However, before I did any of this I would check and see if maybe you actually have 480V Wye and they just did not run the N past the service point because it was not needed.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Hi
I have the existing 1200A service @ 480v, 3-wire
now the new lighting load that requires 277V input are waiting for my decision

What type dry xfrmer do I need???? ...
Adding to previous posts. The norm is to scatter around the plant, 480D/480Y , 75kva, xfm, feeding a 100A/125A 3ph, 4w panel. Feed xfm from a local 480, 3ph, 3W panel

... I am thinking ,
480v , 3-wire 3ph. as primary
480/277v , 4-wire, 3ph. as secondary
(And used only "H" & "0" terminals of primary side for supplying the loads,
not using secondary terminals)
??????? ...
I'm completely clueless on what you have in mind with this.

Couple of other things:
As petersonra suggested, maybe there is an available neutral for the existing system. However, I would not expect this. If the existing service is 480Y (likely), the neutral was only run to the first disconnect.

One other thing: If available, consider 480 ballasts, wire to existing system Line-to-Line. This works really well if the lights are always on or switched in mass (industrial). Office buildings - not so good, you will need contactors.

ice
 
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