Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,977
You can't get 25a out of the neutral without at least 25a on one of the legs.
So, a 25a 2 pole breaker is what is needed.
I disagree. You put 12.5A in L1 of an auto-transformer. That flows and supplies 12.5A to center tap N of transformer and load.
Magnetic coupling sucks another 12.5A in L2 of auto-transformer (note I said "in", not "out", at any given instant it is flowing in opposite direction not same direction as current in L1), and supplies a second 12.5A for 25A in N.
The key here is to think in terms of current which is not "in phase" as you like to say about split-phase systems, but rather current at 0 degrees phase or 180 degrees phase. Same direction or opposite direction.
There is never 25A flowing in L1 and out L2. It is one big inductor, can't get more than a fraction of an amp to flow at 60 Hz. The only way to have 25A flow in L1 is to have 25A flow in L2. They are flowing in opposite directions. When the meet in the middle, they both flow out N for 50A. And that is 2x the transformer's rating.
12.5A I say it is.
This is NOT an isolation transformer, where current flowing in secondary allows current to flow in L1, out L2.