In an overhead service drop for a residential service, where does the source transformer get its ground besides the actual center tap on the windings. The water pipe is in the ground and there has to be that connection through the actual dirt ground.
The Golden Rule - "The man with the gold makes the rule"
The utility will drive a ground rod at the pole that supports the transformer, as well as additional ground rods at every third pole or so. Different utilities will have different rules based on local ground conditions and the likelihood of lightning strikes.
Re: Water pipe ground/ground rods#41390 08/25/0404:47 PM08/25/0404:47 PM
Not exactly, the grounding electrodes installed at a service will not help clear a fault at 120 volts.
They may help with lighting and a power company fault that sends high voltage onto the neutral.
250.4(A)(5)Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path.
The neutral conductor through the bonding jumper is the Effective Ground-Fault Current Path back to the source for 120 volt ground faults.
Bob Badger Construction & Maintenance Electrician Massachusetts
Re: Water pipe ground/ground rods#41393 08/25/0406:36 PM08/25/0406:36 PM
Bob I agree also. I think aldav53 is a bit unclear as to the purpose of grounding hence the confusing question.
The "ground" is not current carrying. The unbalanced and fault current is carried by the neutral conductor that connects to the transformer center taps and runs from pole to pole and into every service.
This neutral is grounded at each service (through ground rods and bonding to the water line) as well as at each transformer with a ground rod. The purpose of grounding is to offer some protection from lightning and primary power crosses as Bob points out.
If the area has a continuous metallic water system, yes the pipe is, in effect, in parallel with the neutral on the poles and also in contact with the earth providing a ground.