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.
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.
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
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.
Shasta, I have done a little bit of research on the XIT grounding system that you suggested. It looks like a very serious product designed primarily for commercial and industrial use. Can you provide any further information on the practicalities - or "how to" - of using this product in a residential application? Do you have a ballpark estimate of what the 10-foot grounding system might cost, and what the incremental installation cost might be? Does this system require specialized installation skills beyond those of an ordinary electrician whose experience consists of more conventional grounding systems?
I would also be interested in a bit more education on your comment that "BTW, you'll never drive a rod yourself..." Is there specialized equipment involved in the installation of a ground rod? Does the process typically involve driving the rod into the ground (visions of driving a railroad spike)? Or, alternatively, does the proces involve boring a hole in the ground, placing the rod in the hole, and backfilling the hole? (Based on my limited reading on the XIT system, it seems that it is installed in the latter manner.)
Any further information you can offer would be much appreciated.
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.
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.
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.
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
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?
The feed from your existing service that will feed the 7.5 kva xfmr will be 2hots, 230v,+ 1 equipment grounding conductor. The equipment grounding conductor will bond, connect, to the case of the xfmr. This ground is for the xfmr only.
Think of this ground as a safety ground.
When you install a transformer of the size you are using you are creating basically a new service. That means the 120 volt secondary side of the xfmr must follow certain safety guidelines to meet the NEC and your local city codes. That is why you need to connect one of the 120 volt leads of the secondary of the xfmr to the neutral bar in the new electrical panel that will be installed. This wire will become the "grounded conductor", the neutral. From this neutral bar a #6awg cu ground wire will run to the main incoming water line ahead of the water meter. This wire is called the "grounding electrode conductor". The wire attaches to the water pipe with an approved water pipe ground clamp. The water pipe is now called the "grounding electrode". This is the primary "grounding electrode" and "grounding electrode conductor" I spoke of in my earlier post. The connection at the main water line is the common ground point that ties your new 120v service to your existing house service.They will both be on the same ground plane. Now back to the neutral bar in the new panel. The electrician will install a supplied bonding screw through the neutral bar into the panel enclosure. Now for the secondary grounding electrode conductor that will go outside to the second "ground electrode" you choose to use. This second ground also connects to the neutral bar in your new panel.The new panel will have two earth ground system connections. Primary,water line ground electrode, and secondary, outside new earth ground electrode. The neutral bar is a Star grounding point now. By the way in your area your water line is probably down 4 to 5 feet deep because of frost. Buried in moist clay the distance, length, from the house to the main trunk connection and beyond.
Back to that neutral bar in the new panel. This bar is where all the new branch circuit neutral wires and equipment grounding wires will terminate...Nec says the neutral shall be bonded to ground at the first point of attachment or disconnecting means and at no point there after. That is why sub panels have seperate equipment ground bars. This is not a sub panel. In this new panel the neutral wires and ground wires share the same connection bar, called the neutral bar. NEC also says the max resistance between the neutral, grouned conductor, and the equipment grounding conductor measured at the receptacle shall not exceed 3 ohms. Also If you can keep the new panel fairly close to the new branch circuit receptacles thats also agood thing.
I have tried to do a better job of explaining things. This is the simple part. Putting it all together in a neat and workman like manner is the tough part. Local codes can vary. Your electrician should know the code of your area.
Cincy: You really can't do a free, engineering project via an audio Forum. That's a bit much to expect, both financially and even more importantly, from a liability standpoint. You are very bright, curious, and well spoken, but, respectfully, and I'll buy the first beer - y'all are drifting into a real project. And, respectfully, if we don't know that ground rods come in 10 ft lengths, and that driving one takes a specialized tool, and is the ultimate in apprentice physical labor, and that there are a ton of NEC requirements to be met, well...
Saying that you may want to consider engaging a freelance (not an engineering company) registered electrical engineer to prepare several drawings on what you wish to do. You can verbalize your electrican through it, but, that is always poor practice. That includes an as-build of your entire home system. Expensive, but hand waving a Journeyman electrican will burn up a stupid amount of hours; and here in N. CA, the billing rate will be about $80/hour.
Not a shareholder, employee, sales rep of any mentioned product. The XIT system is a large, hollow ground rod packed w/ trick material. It is vented at the top to absorb ambient humidity, thusly maintaing a very low impedance with the contacting soil throughout the year despite weather conditions. It is used by Honeywell for their DCS (Distributed Control Systems) in their localized Remote Instrument Enclosures handling plant control of digital inputs/outputs and analog signals in the milliamp level. It is installed in at least one Chevron refinery in California.
It also is, possibly, stupid overkill for a residential app., but in this day and age when 6loons is reviewing new-car priced transports/DAC's, I'm lost...
If your curent system is in good condition, and has a measured reasonable impedance, I wouldn't loose sleep on this...
Shasta, about a month ago, I hired a registered electrical engineer to develop drawings for the modifications to my residential electrical system. What I have been doing in this forum is educating myself so that I can raise the right topics with - and ask the right questions of - my electrical engineer and my electrician.
The service drawings for my system do not contain any detailed specifications for the grounding of the new circuit panel. Without the aid of this forum, I would not have known that there was any alternative to simply grounding the new panel back to the incoming water line that currently serves as the grounding electride for my electric system. And, without any discussion of the topic with my electrician, I am sure he would have opted for this single ground without any discussion and without me being aware of any alternative for a secondary ground. The education Jea48 has provided me regarding the option of installing a secondary outside new earth ground electrode allows me to have an intelligent conversation with my electric professionals that I could not otherwise have even initiated.
Jea48, thanks very much for all the information you have shared. It is very helpful to me and will significantly enhance my ability to communicate with my electrical engineer and electrician.
I'd check out www.equitech.com. They're the people into balanced power; however, they also have different articles that can be downloaded via computer. One of these articles is "setting up an a/c ground." I used one 10' 5/8" copper ground rod. If you use two, they need to be separated by at least 8'. As for putting the ground rod into the ground... Use water. Slowly dribble it into the hole that the rod is making, as you plunge it up and down. The pressure of the rod tip--(like a high heel shoe-pressure per square inch, ouch!), and the water at the hole's developing surface will cut through the dirt in no time. Be careful with that project. I've read multiple grounds can be dangerous. Hope all this helps. Good Listening!
Water method, better not let an electrical inspector catch you do it. The correct way is to drive the rod into the earth. Undisturbed earth. When using multiple rods they must be connected all together with an aproved wire to rod connecting means. Local codes very all over the place on the connecting means to be used.
If you have trouble driving the ground rods into the soil, my electrician used an electric impact hammer, and it worked well.
Jea48, the "water method" that you commented about is the method that was used by my electrician to drive the rod. The power was disconnected and the ground wire hadn't been connected to the rod yet. My electrician works for the one of the biggest electrical contractors in town. Are you saying that what he did wasn't legal? I've heard others use this method in my area as well.
Slv, thats the best way to do it. For those of you who want to do it yourself and do not have access to an electric hammer, you can use a steel fence post pole driver. It will get you within about 30" from the ground. dig around the rod about 6" deep, and you can drive another 6". That last 2' you will need to use a sledge hammer. Aim carefully.
When the rod is driven into the earth it gives the tightest friction fit possible. Using water as a lubricate you are boring a hole for the rod to travel through. As the water migrates into the soil and through evaporation,as time passes, the soil around the rod tends to shrink away from the rod. Does it make that big of a difference? ? It is a lot easier to install with water. And when you drive a rod dry you won`t know if you hit something important, like a Phone line, Gas line, Power line, Water line, Sewer line, you get the idea. The water method is safer. Course you could call for locations. But that won`t cover every thing either. If you do it your self call for locations.
8' distance between rods is better than 6'. NEC just says that is the min. The power company in my area requires 2-5/8 X 8' ground rods driven 8'-4" deep 8' apart 3' out from the foundation of the house for the electrical service grounding electrode. The general rule of thumb is the min distance apart should not be less than the length or the rod used.
How deep can a ground rod be driven? If you go to an Electrical Wholesale House you can buy ground rods with threaded ends. As you drive the rod you can use a couping and connect another and so on. If you live in an area where soil moisture is low this works well generally.