Posted by John T on January 14, 2009 at 19:24:09 from (71.55.26.69):
Yo Jared, I tried to respond to your post earlier but my ISP went down, theres always a good deal of confusion about electrical grounding so in hopes of safety and understanding I copied and pasted what I tried to post earlier........
Jared, just as I advise posters regarding legal questions, I offer the same advice here, BE CAUTIOUS OF LAY OPINIONS REGARDING ELECTRICAL SAFETY ISSUES,,,, The life you save could be your own. Consult with your local authority and engineers and licensed electricians is THE BEST ADVICE because diferent locations do things differently.
Over on johnnypopper.com I posted a short "thesis" covering grounding but Im too tired to look it up and copy n repost it now, were headed to a square dance and Im short on time, but heres your answers and a brief explanation.
NO you dont drive any ground rods for a sub panel located in the same building YES you indeed run 4 wires to it, 2 Hots, Neutral (a grounded conductor) plus an Equipment Grounding Conductor AND DO NOT BOND THE NEUTRAL BUSS AND GROUND BUSS IN THE SUB PANEL.!!!!!!!!!!!!!!!! You do that ONLY at the main service !!!!!!
As far as mother earth grounding, at the Service Entrance you do things like drive ground rod or rods (made grounding electrodes) and bond to other grounding electrodes such as metallic pipes, structural steel etc etc BUT THEN WHERE DOES THE GROUNDING ELECTRODE CONDUCTOR (often No. 4 bare copper) BOND ?????????????? TO THE NEUTRAL.......ITS THE NEUTRAL THAT YOURE BONDING TO MOTHER EARTH NOTTTTTTTTTTTTT THE EQUIPMENT GROUNDING CONDUCTOR although at the service entrance the EGC and Neutral are bonded so sure the EGC also happens to be tied to mother earth. The Neutral is bonded to earth out on the utility lines HV primary and secondary and at your service entrance, perhaps up on the weatherhead riser even before Neutral is bonded to the Equipment Ground Buss NOT any EGC. The purpose of earth grounding the Neutral is to bring the utility and services all to one common best zero reference which mother earth provides.
The sole purpose of the EGC is to provide a dedicated low impedance current return path for FAULT CURRENT ONLY so the breaker trips n saves your life or a fire, the sole purpose IS NOT TO BE SO CONCERNED WITH MOTHER EARTH BUT TO BE A DEDICATED RETURN CURRENT PATH FOR FAULT CURRENT ONLY and mother earth is a poor conductor but that copper EGC back to the panel is a great conductor.
What lay persons have a hard time grasping is the Equipment Ground Conductor has to do with fault current NOT its being tied to mother earth. i.e going around driving rods into the earth and connecting them to the Equipment Ground IS NOT what its all about, its the Neutral that gets bonded to mother earth and at the main service entrance panel Neutral (a grounded conductor) is bonded to the Equipment ground buss so that if a fault occurs the EGC provides a path back for a shorted hot phase conductor to Neutral NOT MOTHER EARTH so the breaker trips. It can accomplish its job as far as fault current return regardless if there were no ground rods taking the Neutral to earth potential. i.e if theres no ground rods whatsoever the EGC can still do its job cuz it provides a return current path, that fault current is trying to get back to the voltage potential which exists between a hot phase conductor and Neutral NOT mother earth, so ground rods or no ground rods isnt the issue........
Got to go, check with local authority and licensed electricians and engineers NOT lay opinions..........
God Bless yall n keep safe
John T Long retired Electrical Engineer and rusty on current codes but still familair with the theory of grounding and Neutrals and EGC etc
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