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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
flex
292 posts
 
Cincy_bob,
Also check Atitec electrolytic ground rods, (www.atitec.com), which are similar to Lincole but may be priced more competitively. It is worth talking to either company before installing this type of grounding - if you're going this far, it's worth understanding the soil content at your place, and the number of rods that are optimal for adequate grounding. The rod is not driven, the hole does need to be backfilled with electrolytic compost to provide adequate soil contact.
fedreams
107 posts
 
The Lyncole system can be laid vertically or horizontally. They make kits for either. Lyncole is a US based company and uses high quality part than some of the other systems manufactured in China or other places.
This system will is probably one of the best grounding systems out there at this time.
jea48
2,944 posts
 
Cincy bob, In your original post you said your were going to feed all your loads from one line. If you configure the secondary of the xfmr, and wire the new panel for 120/230 volt, then only use one line to neutral and not the other line to neutral for loads you will only be using half of the 7.5kva rating of the xfmr 3.75kva. Not knowing what your xfmr looks like, Most of the single phase xfmrs I work with have dual primary and secondary windings. From the description you gave in your last thread it sounds like you have at least dual secondary windings. To get 120/230v the two secondary windings are seriesed together. The center point being the common of the two windings, leads L1 and L2. L1 to L2 230v L1 to com 120v L2 to com 120v. If you want to get the full 7.5kva of the transformer you want to parallel the two secondary windings. Follow the data plate on the xfmr. My best recollection is tie [X1 to X3] line 1, [X2 to X4] line 2. Like I say check the data plate on the xfmr. With the two windings paralleled L1 to L2 will be 120Volt. Line 2 will tie to the neutral bar in the new panel. L1 will terminate on the single pole 60 amp breaker I discribed in my previous post. The panel you buy will be a main lug only type 120/240 single phase 3wire. install a jumper wire across L1 and L2 of the main lugs of the panel. Now you have a single phase 120V panel. Install breakers in any space you want. I dont care what you do for the secondary grounding electrode. But the primary grounding electrode shall be your copper incoming water line. Your existing electrical sevice uses this grounding electrode for it`s primary ground and the new 120V derived system shall bond to this grounding electrode via the grounding electrode conductor.
jea48
2,944 posts
 
Cincy bob, I just read your second post again, about the transformer. The word "taps." Make sure you are getting a true isolation xfmr. Not a autotransformer.Autoxfmrs are not isolation xfmrs. Single phase autotransformers have taps. Isolation transformers have totally separate insolated primary and secondary windings. They can have AL or CU windings. For even better isolation you can buy a "Electrostatic Shield" type xfmr. The electrostatic shield is installed between the primary and secondary to attenuate some of the source line interference and common-mode noise. I guess what I am trying to say make sure you know exactly what you are getting...
Just curious What part of the country do you live in? North, Northeast, south, southeast, southwest? Curious about the soil and moisture in your area.
In my previous post I used the word "shall" in refering to the primary grounding electrode. I forgot to include NEC requires, at least my understanding of The National Electrical Code, and the electrical inspectors in my city.
Cincy bob, ask lots of questions of your electrician. Make sure exactly what you are getting and paying for.

Best of luck
cincy_bob OP
270 posts
 
Jea48, thanks for all your input. It is really valuable to me as I lack personal expertise in this area. Here are some answers to your questions:

1. Soil and Moisture - As my user name implies, I live in the Cincinnati, Ohio area. Our soil in this area involves a lot of clay. We tend to have normal midwestern weather with a fair amount of precipitation yearound but occasional droughts in the summer months. Let me know if additional information would be helpful in this area.

2. Isolation Transformer - My isolation transfomer is an MGE Topaz isolation transformer that is described in the following web link:

MGE Topaz 100 Installation and User Manual

This web link will lauch a pdf file that contains the full user manual for my isolation transformer. The specifications for the unit are contained on page 11 of the document. My unit is model no. T-100H-7500. It is a hardwired 7.5kVA transformer (see pg. 12 for the specifications of the various model numbers).

The unit provides 140dB of common mode noise attenuation and 65dB of normal mode noise attenuation. I believe the transformer also provides the electrostatic shielding that you mentioned in your latest post.

By the way, my use of the word, "taps," simply shows my inexperience with the subject matter. I had no technical basis for the use of that term.

Based on the advice in your latest post, it sounds like I should use the transformer to step down the 240V primary voltage to 120V at the output stage.

It would be a lot of help to me if you would explain a bit more to me about the primary and secondary grounding electrodes in my system. If I understand your posts to date, you are suggesting that, to comply with code and safety standards, the grounding electrode on the primary stage of the isolation transformer must be tied back to the grounding system at my main electric panel in my house (i.e., the clamp that is attached to my water pipe service where the service enters my house).

When you refer to the secondary grounding electrode, are you referring to a second ground connection from the secondary side of the isolation transformer? Did I understand your first post in this thread to suggest that it is best to have a ground for this secondary side of the transformer that is independent of the water pipe ground that is used as the primary ground for my electric system? I have seen a lot of cautionary advice about the use of two separate grounds within an electric system. The cautionary advice seems to say that it is never acceptable to have two separate grounding systems for two parts of an electrical system. Can you clarify this part for me?
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