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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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128x128whart
jea48
4,416 posts
 
>>"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."<<
>>>>>>>>>>>
Find another Electrician! You may want to ask what else he is doing that does not meet NEC and your local codes.

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Gs5556's post is right from the text book, NEC. Follow his post and you will meet NEC code.
The earth shall not be considered as an effective ground-fault current path back to the source.
whart's avatar
whart OP
3,033 posts
 
Many thanks to all of you, and to Nsgarch, for the timely responses. Work will be done by the book, according to Code and to Hoyle. The balanced power idea is also intriguing. I will let you know how it goes and will scream if I have questions in the midst of it. Thanks again, everybody.
jea48
4,416 posts
 
Whart, glad to hear you will not be using a separate equipment grounding conductor and ground rods for the sub panel that does not connect back to the main electrical service panel grounding electrode system.
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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."<<
>>>>>>>>>>>>

Just curious how did the electrician do this? Did he tap into the Hot conductor/s ahead of the main breaker, of the main service electrical panel? What size is the main 2 pole breaker, 100 amp, 200 amp? Did he install a new breaker and enclosure at this tapped location to protect the feeder that runs to the new sub panel? How did he connect to the neutral conductor ahead of the main service panel? How far is the sub panel from the main electrical panel? What size of wire did he install to the new sub panel? How many conductors, wires?
nerspellsner
41 posts
 
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.
kenyonbm
141 posts
 
Whart, what is the problem (power, safety or audible) that you are trying to cure? Why do you need a separate panel? Maybe there is a simpler way.

>>By using separate or multiple grounds, the possibility exists that a short circuit may be routed away from the breaker, causing a dangerous situation.<< Only the hot side of the circut is fed through the breaker, so multiple paths back to the panel are immaterial. The current has already been through the breaker and cannot be routed away. The ground wire itself is a separate path, parallel to the neutral.

I do agree that not connecting new grounds to the exsiting panel or connecting the subpanel neutral to ground anywhere but the main panel are REALLY BAD IDEAS.

Let's talk about the underlying problem and try not to create new ones.



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