Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
I have 277/480 coming in and same voltage coming out. How can that be?
Xfrmr Voltage
- Thread starter Alwayslearningelec
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Could be the supply system is 3 phase, 3 wire, 480 volts without a neutral. The tranformer with the Wye secondary creates a neutral.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It could be a dedicated isolation transformer. Maybe the load is sensitive to power quality issues.
But based on it being a called an LP panel, I agree with infinity.
But based on it being a called an LP panel, I agree with infinity.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yeah, I saw LP and assumed lighting panel which would make sense for 480Y/277 volts.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Isolation transformer with the same primary and secondary voltages
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
No, you probably do not, you likely have 480 Delta coming in, which is why they added this transformer.
- Location
- Illinois
- Occupation
- retired electrician
The is a delta/wye transformer. I don't see a 3 wire 480 volt delta circuit as being the same voltage as a 4 wire 480Y/277 volt circuit.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
If you actually have 480/277 coming in, it’s just an isolation transformer, but you may have a 480 only service, and the are creating a neutral.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Still could be a delta wye, even if the incoming is 48/277. Most likely though a delta 480 volt service. The note we do not see probably explains it.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
FIFY.
Even if the service is 480/277V and the transformer is wye-wye, the neutral on the primary side should not be connected.
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Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
Wow this is confusing.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The feeder is only 3 wires so it is only 480V, even though it may be coming from a 4 wire source.
Because there is no neutral in this particular feeder a transformer is being added to create a 480Y/277V 4 wire circuit.
Every thing else is just noise.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
FIFY.
Even if the service is 480/277V and the transformer is wye-wye, the neutral on the primary side should not be connected.
If it is actually a wye-wye transformer (rare, but possible), then you will need to connect the primary neutral to get stable L-N secondary voltage.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If it is a 480/277 source, then the question is, why is there a transformer to feed a “lighting panel”? You already had 277V for the lighting…
As I mentioned in Post #6, I have seen that fairly often where the available fault current at the 480 panel is extremely high and transfgotmer is added to provide a source of power to address low SCCR or breaker AIC.