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HVAC School - For Techs, By Techs

Apr 18, 2017

In this podcast episode, Bryan talks about grounding and some common misunderstandings related to ground, neutral, ground rods, and lightning.

The common phrase that "current goes to ground" is a myth. The transformer (or the power source) that feeds a building creates a potential difference in charges (voltage); current is the motion of electrons between a difference in charges.

A transformer has three terminals: two legs and the XO terminal (neutral). You have 240 volts between legs and 120 between each leg and the XO terminal. The leg of power going into the transformer is split into two in a single-phase application, so the sine waves are completely out of phase with each other. When you connect to a transformer, all of the power is either a balance between the two legs or is between the legs and the XO terminal (neutral); it NEVER goes to ground. If any power is traveling to "ground," it is traveling to the ground and going back to the source because there is no other path. Power travels to the ground and then to the source when neutral isn't properly bonded to ground.

Another common myth is that the current always takes the path of least resistance. The current does not always take the path of least resistance; it may take all appropriate paths.

All equipment is grounded to create a ground fault (this is called "grounding"). Then, it should be connected to a ground rod. Grounded assemblies attempt to dissipate high-voltage occurrences, such as lightning strikes and massive surges from distribution lines. Lightning is a very high-voltage DC phenomenon that can be fatal to people or equipment. So, dissipating electromagnetic pulses to ground is much safer.


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