Quote:
Originally Posted by A27Hull  Thanks to you both Zmix and Mike,
Its beginning to make sense. I'm a beginning electronics tech with a nasty habit of asking "why" all the time. I guess thats why I'm doing engineering as well. I have a lifetimes worth of knowledge to learn still.
I made a block diagram to simplify the situation. It would seem that in a three prong system, shorting either neutral or hot to the chassis by any means (whether circuit ground or fault) would create a current loop between the earth ground and that neutral or hot wire. Anything touching the chassis would become a impedance mismatch to earth, causing a voltage drop across that object and a current flow of some amount. In a sense the object creates an additional parallel path to earth.
If this is true, why connect the circuit ground to chassis/earth at all? |
To eliminate a shock hazard, for one thing...
Do this: with an amp that is NOT grounded and with a VOM measure on AC scale between the chassis of the amp an a KNOWN AC ground point, an amp that is grounded for example and see what you get...with the ungrounded amp ON the other makes no difference.
I have measured over 150 volts on an amp chassis before.
Also the noise, stray currents ect. want and need to go to the source ground point to be dissipated or lowered to a very low point.
Noticed I said the SOURCE ground point, a separate and unconnected ground rod will NOT be the same.
Most gear I have seen that was properly designed was cleaner and quieter when grounded.
A growing problem in clubs ect is harmonic distortion on the AC circuits that the band uses for their amps ect, and if it's bad enough can truly destroy audio gear.
A GOOD, dedicated home run circuit is the best, and IM refering to all 3 wires...
The problem is most clubs will NOT provide this.