I am coming off a 240v delta 3phase panel and putting in a 3phase step up to 480v delta-delta 75kva transformer. I am having trouble figuring some things. Code says 450.3 (c) shall be protected by primary fuses. Can i use the breakers and the fuse. I thought you couldn't put fuses in series with breakers.
240v delta step up to 480v delta
- Thread starter casjos
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Amazing... I've installed and inspected transformers for years and never even noticed 450.3(C) 
I'm not sure what this is referencing.,
To the best of my knowledge for your application, you follow 450.(3)(b) and 240.21(C) and 250.30
I'm not sure what this is referencing.,
To the best of my knowledge for your application, you follow 450.(3)(b) and 240.21(C) and 250.30
- Location
- Illinois
- Occupation
- retired electrician
I believe that "voltage transformers" are those installed in association with metering for higher voltage systems. They are not the standard tranformers that we install in buildings.
As far as installing fuses and breakers in series, there is no code rule that says you can't.
As far as installing fuses and breakers in series, there is no code rule that says you can't.
kwired
Electron manager
- Location
- NE Nebraska
The FPN following that section even gives us some clue that it is talking about instrument transformers and not power transformers.
Why a 480V delta secondary?
Why a 480V delta secondary?
Being that I had worked for a transformer manufacter as a sales engineer I alsway asked my customer if they had a good reason for the 480v delta secondary and I usual got the answer trhat "they didn't need a neutral". The I asked if they needed to ground it?
Using a 480v Y provides the opportunity to ground the X0 which you don't have to bring out as a neutral as often is done this MCCs.
It's much better than corner grounding a 480v delta ot providing ground detection with an ungrounded 480V D.
Why a 480V delta secondary?
Being that I had worked for a transformer manufacter as a sales engineer I alsway asked my customer if they had a good reason for the 480v delta secondary and I usual got the answer trhat "they didn't need a neutral". The I asked if they needed to ground it?
Using a 480v Y provides the opportunity to ground the X0 which you don't have to bring out as a neutral as often is done this MCCs.
It's much better than corner grounding a 480v delta ot providing ground detection with an ungrounded 480V D.
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