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stepping down voltage

stepping down voltage

stepping down voltage

(OP)
I need a single 120v, 20A circuit from a 480v/277v panel, what is the best way to do this?

RE: stepping down voltage

Look for a 2.4 kVA single-phase transformer with 277 V to 120 V windings.  That's the minimum calculated size that will work, so you may have to get one slightly larger to line up with what is commercially available.

RE: stepping down voltage

(OP)
For current protection should I only need a 15A breaker in the 277v pannel, or should something be on th 120v side.  My problem is the CODE makes it sound like I only need protection on the line side, but the MATH says that 15As on the line side is to large. I don't beleive they sell a 10A breaker that I can put on the line side, or do they?

RE: stepping down voltage

I agree that the MATH is wrong for 15A on the 480/277 line side to protect a 20A 120V circuit.  I am not sure where you got that requirement, but perhaps it was a maximum allowable rating?  I also think that putting it on the line side is safer.

I am not sure who "they" is regarding to making breakers, but how about a fuse?  You would need to make sure that your fuse had a sufficient voltage rating but this shouldn't be a problem.  I just did a quick check from my favorite parts supplier and found a 5A, 500V fuse for $1.40 (USD).

I am sure that there are breakers in that rating range too, but they will be more expensive.

 

RE: stepping down voltage

If you use a fuse you will be much happier if you spend a little extra the first time and use a dual element (time delay) fuse.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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