1. Home
  2. tech-talk
  3. 1102374689

Installing an AC Grounding System, Need Advice

Later this week, my electician will begin work on my electric project, which will involve the installation of a 7.5kVA isolation transformer that will be fed from a separate meter tap. The isolation transformer will be installed in front of a new dedicated circuit panel that will house the dedicated circuits that will feed my listening room. All the dedicated circuits will be fed from the same side of the bar in the new panel in order to maintain consistent phase.

As Sean has advised in a separate thread, I know it is important that I check - and upgrade as necessary - the ground for my AC system. (My house was built in the late 1950s, and, from the looks of things, not much has been done since that time to upgrade the electric service. So I am nearly certain that I will find the grounding system leaves much to be desired.) I also know from discussion in various other threads that it is important for the entire electrical system in my house to share a common ground. So I expect that I will need to upgrade the grounding system into my main circuit panel and then tie the isolation transformer and the new dedicated panel back to that same grounding system.

The work on my house is being performed by a qualified electrician, but, as I have noted in other threads, I would like advice on the audiophile details that can make a difference in the sound (in this case, the noise floor) of my system. Perhaps I should also mention that my plan involves installing a separate dedicated circuit for each of my seven components. Given that this sort of a set-up is more prone to ground loops, I am interested in advice regarding how to avoid them with this set-up.

With that as background, would any of the resident experts be willing to share with me the details of how to install a high quality grounding system for my AC power? I would appreciate as much detail as possible regarding the materials to use as well as installation advice.

I have read some advice in other threads recommending two separate copper grounding rods driven into the ground relatively close to each other with a weather-proofed connection between the two rods that is, in turn connected to the electrical system. I have also seen some advice that I believe involves wiring one of these connected ground rods to the main house circuit panel and the other connected ground rod to the audio portion of the system (i.e., in my case, the isolation transformer and the new dedicated circuit panel). Please let me know if this is headed in the right direction and, if so, please help me to fill in some details (dimensions of the copper, advice on how to drive it into the ground without mangling it, distance between the redundant rods, any other details you see fit).

As always, thanks for your help and patience.
cincy_bob
jea48
2,944 posts
 
You say a 7.5kva xfrmr. 230 volt primary 120 volt secondary? If it is indeed 120v out your electrician will bond one leg of the secondary to ground. This will become the grounded conductor and will terminate on the neutral bar of your new electrical panel. The electrician will bond the neutral bar to the panel enclosure with the supplied bonding screw. For the grounding, do you have a metallic water service, copper? This will be your primary ground electrode. Run a #6 awg min cu wire from the new elect panel neutral bar to a new water pipe clamp installed on the water pipe ahead of the water meter. Clean the water pipe with sand paper to a brite copper like new look. This #6 awg wire is called the grounding electrode conductor. While your electrician is at the meter location have him clean up your main service ground clamps and water meter jumper wire. Next ground to run is the secondary grounding electrode conductor. Not knowing where you live and the type of soil and moisture you have your electrician should know best. Drive two 10ft ground rods out side your house, at least 6ft apart at least 10ft 4" deep. Run a #6 awg min cu wire from the neutral bar of your new elect panel to these new ground rods.For these rods try to pick an area closest to your new panel. Your electrician will know the proper procedure for bonding the wire to the rods this can vary in areas due to local codes. Note, If the electrician feeds the 7.5kva xfrmr with romex run #10-2 w/grd awg cu min. Ground the case of the xfrm from your main house service panel. If the xfmr should have a short the fault current will travel back on this equipment grounding conductor and cause the breaker feeding the xfmr to trip open. With this xfmr you are creating a new seperately derived ac system. In the new panel board install a single pole 60 amp breaker for the main breaker. I recommend Square D QO panelboard and breakers.

Hope this will help.
shasta
155 posts
 
Sigh, stand back for a rush of unsafe, uniformed advice; starting off with 2 separate ground rods. There's only one way to do a grounding system (is this a house under construction?) and that's at least NEC minimum, and even that can be improved on. Any cock-eyed deviations from that will induce laughter from your electrician and scowls from the inspector.

Do a real, Code-defined, isolated ground install for *each receptacle. Any Journeyman electrician should understand this.

Install a Lyncole XIT ground rod system. Watch your electrical contractor's eyes bug out as they start to call you Sir and Mister. If this is an existing house, leave the current rod in place, and use the XIT as an adjunct. Scrub, clean, and retighten all exsisting connections on the existing rod. BTW, you'll never drive a rod yourself...

If an exist. house, call the utility and get a 4 hour disconnect. Clean and retorque the incoming lines at the service panel. Then, clean and retorque everything on the load side of the main breaker.

*I* would have done metallic conduit; but the twisted wiring is certainly a nice feature. That's why they make vanilla and chocolate...

Obssesive was actually a left-hand complement-- *grin*. When I bought my condo several years ago, I replaced all switches and receptacles w/ Leviton 20A Spec grade devices. Wire ends were cleaned, everything backwired clamped, and I purchased an Armstrong torquing screwdriver for finalizing the connections; required per NEC 110.3(b).

Recap: Torque all connections, new or old. Isolated ground for every receptacle. XIT ground rod. Have the impedance checked on the grounding electrode conductor, and shoot for *way under the NEC 25 ohms number; which the XIT should deliver.

Strike the set, it's a wrap.
sean
6,229 posts
 
Shasta: From what i can tell ( i am NOT an electrician and don't understand all of your terminology ), your post seems to advocate a redundant ground system for the AV system that ties back into the main ground system. Is this correct? If not, could you either explain what XIT ground rod system is or provide us with a link that shows pictures / offers an explanation?

Other than that, your ideas of shutting down the AC for several hours and cleaning all of the existing contacts is a great idea. As i've posted before, the lack of continuity in a connection, especially to ground, can result in poorer performance than expected. Sean
>
cincy_bob OP
270 posts
 
Jea48 and Shasta, thanks for your responses.

Jea48: The input to the isolation transformer will be 220V on the primary side. The transformer offers different taps to allow either 220V output or a stepped down 110V output on the secondary side. My electrician was planning to feed the new dedicated panel with the full 220V of output from the secondary side of the transformer. If this configuration does not make sense given my desire to run all the circuits from only one side of the bar, I would be interested in your observations and advice.

Regarding the water service in my house, it is metallic (copper) water service. I can see that there is a ground clamp on my water service ahead of the meter where the service enters my house. I believe that ground wire is tied into the ground for my AC service on the other side of the house. (I have not traced the wire in order to verify this; however, the ground wire runs in that general direction before it disappears above some non-removable ceiling tiles, so it is a safe bet.) I think I remember seeing a ground rod driven into the ground outside my house in the near vicinity of my electric service that I assume is also tied back to my main electric panel

Shasta: My house is not under construction. On the contrary, it was constructed in the late 1950s. As mentioned above, I believe my electric system is using a ground rod that is driven into the ground in the near vicinity of my electric service. Either I or my electrician will need to fish around in the ivy outside my house to verify the existence and location of that ground rod.
More to discover