From my understanding of electrical circuits, it depends on the circuit. DC circuits generally don't produce emf but AC circuits do. For instance, I have a far infrared heating pad that is transformed to a dc circuit and has zero emf. I verified this by testing it. I also tested the old type of heating pad which was an AC type. It pinned the needle on my tester. Having a high quality emf meter around has been a big plus. You can see where these fields are high in your home. Its incredible to see just how high emf is where the main power comes into your home which fluctuates depending on the draw at any given moment.