Weird Transformer Talk

In this podcast episode, Eric Mele joins Bryan for some weird transformer talk. They discuss corner-tapped transformers and some thought experiments.

We hadn't been able to get our heads around corner-grounded transformers until recently. “Grounding” doesn't necessarily change the phase or lead that you ground. If you take the secondary of a 24-volt transformer and measure from your two colors, you'll measure 24v. However, if you connect a lead to ground, you'll still read 24v. (Don't ground both, or you'll get a short.) Ground is just a path back to the power source. Electrons don't suddenly “leak” from something connected to ground.

Grounded and neutral conductors can potentially be dangerous. There can still be potential even though your leads wouldn't pick it up. In residential HVAC, we're used to seeing neutral and ground connected at the main distribution panel. However, it's not always okay to connect ground and neutral or use ground as a current-carrying conductor.

If you've got split-phase power going into a regular home, you've got 120 volts 180 degrees out of phase with each other. If we don't have a center-tap neutral, it would function similarly to a 24v transformer. In that case, it's not necessarily unsafe to read 0v on neutral. We get tripped up because we think in terms of using a meter, not in terms of actual potential voltage.

In a delta configuration, you will have a high leg connecting to neutral (B phase is usually high; A and C phases are usually normal). You can't really center-tap a delta, so you have to tap the center of one phase.

Eric and Bryan also discuss:

  • Working out of a truck vs. a van
  • Shunting high-voltage spikes to ground
  • Center-tapped transformers and “wild legs”
  • Ground is NOT necessarily the earth
  • Hot legs on the primary AND secondary

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