hhsting
Senior Member
- Location
- Glen bunie, md, us
- Occupation
- Junior plan reviewer
To reduce neutral currents transfromer primary. Transformer secondary point is grounded to bldg steel.
Last edited:
Isolation transformer
- Thread starter hhsting
- Start date
- Status
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If primary is delta there will be no neutral to have currents in, even if you pulled a neutral with supply conductors there is nothing to connect it to.
Does your primary have an H0 terminal? If all it has is H1, H2, H3 it is likely delta primary winding.
If it is delta primary to delta secondary (three wire secondary) then the secondary is protected by the primary overcurrent device.
Can you provide a picture of the nameplate, the diagram, or the manufacturer's specification, please?
hhsting
Senior Member
- Location
- Glen bunie, md, us
- Occupation
- Junior plan reviewer
Link to the transformer manufacturer: https://store.maddoxtransformer.com/products/3-phase-480v-delta-480v-y-277v?variant=2194327896073
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You said link to manufacturer, they likely have delta and wye primary possibilities, though as been mentioned already it would be most common to see delta primary on smaller low voltage transformers. A wye primary unit would likely be more of a non stocked, special order kind of item.
hhsting
Senior Member
- Location
- Glen bunie, md, us
- Occupation
- Junior plan reviewer
I realized its wye on about post #10 checked manufacturer site. Posted the link its not auto transformer.
Sent from my SM-G935U using Tapatalk
Sent from my SM-G935U using Tapatalk
What is being isolated from what?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Most of the thread has been about verifying what you actually have. If it is indeed delta -wye your question was answered in post 2.
That point seems to continue to be missed......
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
But, from the OP:
"primary 480V three phase to secondary 480V/277V three phase"
The secondary must be wye for the 277v to be there.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Correct
- Location
- Illinois
- Occupation
- retired electrician
It really doesn't matter what the secondary is, if the secondary has a neutral, the transformer primary OCPD cannot be used to protect the secondary conductors.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
:thumbsup:
Even though the secondary neutral is connected to ground of the isolation transformer?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The secondary is a separately derived system. There is no additional "ground" that is associated with the transformer, ground is defined in art 100 as "the earth". "Grounding" the secondary neutral is making the secondary neutral the same potential as earth, which was also done to the grounded conductor of the primary circuit at it's source, unless it is an ungrounded supply, so that makes both primary and secondary same potential at that point, however a grounded conductor that is a normal current carrying conductor isn't supposed to be "grounded" again at another location as a general rule - that can result in undesired currents over undesired paths.
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
I was under the impression that single phase single voltage and 3 phase delta to delta could be protected by Primary OCPD. Does that rule out a 4 wire delta?
- Location
- Connecticut
- Occupation
- Engineer
Yes
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
I ment a Delta 4 wire. but 240.4(F) agrees with you David.
- Location
- Connecticut
- Occupation
- Engineer
I said yes, because I knew what you meant :happyyes:
- Status