If the ground wire is only connected to a ground rod or an underground metal or copper water pipe, the circuit breaker usually will not trip if there is a short to ground. There has to be a connection to the neutral from the ground to trip the breaker. Power from the hot wire goes to ground and then to the neutral to trip a breaker in a ground fault. A sub panel does not have the neutral and the ground connected (bonded) together, the main panel does. If there was a ground fault or a short circuit on one of the circuits in the sub panel and there was two seperate grounding systems for each panel this is what will happen. The power will go to the sub panel ground rod and try to go through the earth and make a connection to the main panel ground rod which is connected to the neutral so the breaker will trip. You can not use the earth as a grounding conductor. The main neutral wire from the street makes the breaker trip and not the ground. Thats the reason that all grounds have to be connected together so the fault can go to the neutral and trip the breaker.
Yet another Grounding Question-Separate 'Earth'
I emailed this question to Nsgarch since he gave advice on another thread respecting the separate grounding of a dedicated subpanel, but at the risk of making some of you read yet another grounding question, I decided to post it as well. Here goes:
My electrician has installed a separate subpanel for the audio system which is 'upstream' even of the main breaker panel in the house.
It will have several dedicated lines, each with a 20 amp breaker (Square D) running separate grounds to Hubbell Hospital Grade Outlets. I was concerned about the potential 'difference' among these separate lines- one will support mid-hi-freq. amps, others, the subwoofer amps, and a third, the lower powered front-end equipment (preamp, phono stage and TT- no digital). I do have one of those Granite Audio thingies which permits me to 'star ground' everything to a single point in the system, FWIW.
But, and here's the really critical question- my electrician has proposed a pair of separate ground rods about 10' from the main ground for the rest of the house electrical system, and in his view, the audio system subpanel would be grounded just to these new ground rods, not connected, by ground or anything else, to the rest of the house. In one of Nsgarch's postings on this subject, he indicated that there could be a differential in the two different panel groundings which could put current to the 'neutral' and create a shock risk. As I understood the advice, it was to make sure that the audio subpanel shares the same 'earth' ground as the rest of the house.
Could you comment?
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My electrician has installed a separate subpanel for the audio system which is 'upstream' even of the main breaker panel in the house.
It will have several dedicated lines, each with a 20 amp breaker (Square D) running separate grounds to Hubbell Hospital Grade Outlets. I was concerned about the potential 'difference' among these separate lines- one will support mid-hi-freq. amps, others, the subwoofer amps, and a third, the lower powered front-end equipment (preamp, phono stage and TT- no digital). I do have one of those Granite Audio thingies which permits me to 'star ground' everything to a single point in the system, FWIW.
But, and here's the really critical question- my electrician has proposed a pair of separate ground rods about 10' from the main ground for the rest of the house electrical system, and in his view, the audio system subpanel would be grounded just to these new ground rods, not connected, by ground or anything else, to the rest of the house. In one of Nsgarch's postings on this subject, he indicated that there could be a differential in the two different panel groundings which could put current to the 'neutral' and create a shock risk. As I understood the advice, it was to make sure that the audio subpanel shares the same 'earth' ground as the rest of the house.
Could you comment?
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