The solid state logic of modern computer chips uses DC impedance.
( Yes, impedance is not just an AC phenomenon. In DC SWITCHING CIRCUITS the impedance exists for a fraction of a second upon a change in state. This wave pulse is the actual basis for triggering the logical state function from 1 to 0 or from 0 to 1.)
One aspect of such high speed switching is the absolute need for a stable ground state -- ie ground path. If the last pulse is not instantaneously flushed/drained to zero faster than the next machine cycle ( switching frequency ) then logical errors pop up. What should be now zero ( 0 ) is still strong enough to read as one ( 1 ).
Modern chips have just about half of their internal wiring dedicated to ground paths. That's why you see such wide ribbon cable running to and fro. When you discover the pin-outs you'll find repeated isolated paths to ground so that each drain run is wide open for each pulse.
Ultimately, the whole system needs a stable ground with a drain to the ultimate earth. Even laptops have ground drains when they are hooked up to the power supply.
When a laptop is running on battery power, it gets its stable ground by reference to the battery pack.
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Other items that use DC impedance: VFDs...
AC is rectified into a capacitor 'tank' -- then IGBTs switch the DC at ultra speed and efficiency to 'stack up' AC wave forms at the desired frequencies. ( Study Fourier Series and Wave Physics for the reason it works.)
At higher frequencies such 'tank' circuits produce metal melting induction beams. You'll only find these in industry since they are high cost, high power, high output.
More commonly, intelligent ballasts/power supplies use the same method to power high efficiency fluorescent lighting. In this case, the power supply doesn't care what the input voltage is! it can handle 100 to 300 V Ac and still work. ( the 120 & 277 V rating on the package is just an industry term of art. 208 or 240 volts would work, too.)
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WRT your situation, the grounding path/drain line does not have to follow the hot & neutral. You can even use bare copper outside of a raceway. You do want to bond it back to the GEC so that you have a one point connection between your neutral and GEC and EGCs.
Ground loops are another no-no for digital logic.
Cheers.
Last edited by Tesla; 06/10/10 09:04 PM.
