Detached garage grounding

The detached shop of the house I am moving into has power split directly from the meter. The house and shop only have 2 hots and a neutral running to the panel. Both panels are treated as main panels and the buildings each have their own ground rods driven. I talked briefly with an electrician and he said detaches structures should have 2 hots, neutral, and ground run so the building grounds are tied together and the shop panel should be wired like a sub panel.
 
I'm slightly concerned I'm going to burn up equipment due in a storm due to a ground loop. For network I could go fiber, but I still need to address the security and audio side. When I look at the OmniPro expansion panel manual it only mentions to connect the A/B data lines. For audio the plan is to use a balun over Cat5e and have an amplifier in the shop. Since the grounds aren't tied between the OmniPro panels does this remove the issue? Or should I rerun the service lines between the shop and house so the structure grounds are tied?

For my situation I do not connect my ground systems together either. My shop building has several ground rods to connect to all equipment shells but the neutral is only bonded at the house service. My shop service is a sub panel from the main though. I figured it best to just look at it from the equi-potential aspect keeping the equipment in one zone tied together and not introducing stray voltages from another zone's ground system into the mix.
 
The trouble with all this is when you bring signal lines from one zone to another. This definitely becomes an area of disagreement from most practitioners. Running conductors between grounding zones for lightning probably won't help much or at all and may cause more problems spreading the disturbances around to more equipment. Long conductor runs end up being high impedance to the high frequency components in lightning anyway and don't get there. Close local grounding is the best for that.
 
After much research and hearing arguments from many different viewpoints, in the end it was up to the Inspector for my area and he agreed with my approach, don't connect building grounds together and do not bond your neutral in two different spots. If the buildings are hundred of feet apart you may want to reconsider that one. Every feed from a utility transformer has a bond to their ground rod in an attempt to keep each grounding zone at the same potential rise as the transformer neutral.
 
For big distances between buildings look towards fibre optics and good isolation practices on signal lines. You will never really know if what you did was enough until you find out it wasn't.

LarrylLix said:

For my situation I do not connect my ground systems together either. My shop building has several ground rods to connect to all equipment shells but the neutral is only bonded at the house service. My shop service is a sub panel from the main though. I figured it best to just look at it from the equi-potential aspect keeping the equipment in one zone tied together and not introducing stray voltages from another zone's ground system into the mix.

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I'm not sure I am following your setup. What do you have run from your main building to the second building? 2 hots, neutral or 2 hots, neutral, and ground? At the second structure sub panel you have the ground and neutral bus bars isolated. How are the grounds connected? My understanding is that the feeder ground from the main structure goes to the ground bus bar and additionally a ground rod is driven and also connected to the ground bus bar. Otherwise the ground rod has no reference to neutral and would be a floating ground.
 

LarrylLix said:

fter much research and hearing arguments from many different viewpoints, in the end it was up to the Inspector for my area and he agreed with my approach, don't connect building grounds together and do not bond your neutral in two different spots. If the buildings are hundred of feet apart you may want to reconsider that one. Every feed from a utility transformer has a bond to their ground rod in an attempt to keep each grounding zone at the same potential rise as the transformer neutral.

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The issue with my setup is there is no ground wire between the structures. The neutral and ground bus bars are bonded and ground rods are connected to the ground bus bar in both buildings. The previous owner built the shop back in the 90s so it has been setup this way for 20 years. He only has power to the shop and no low voltage runs or equipment. Although looking at this another way maybe there is no issue as with the neutral and ground bonded at both buildings the neutral wire between the buildings essentially becomes a ground tie as well.

http://www.doityourself.com/forum/electrical-ac-dc/361941-detached-building-subpanel-grounding-feeding.html

I'll touch on the important points between '05 code and '08 code:

#2 aluminum used to be allowed for 100A subpanels under an interpreted wording of a code article. They have now explicitly changed the wording so that #2 aluminum is good for 90A to a subpanel.

Three-wire feeds (no ground) used to be allowed to an outbuilding provided that no other metal pathways like a water line or phone line were present. Now, four-wire feeds are mandatory, no exceptions.

The ground rods are required in either case, and they should be connected to the subpanel ground bar with #6 copper wire. When a three-wire feed is used, the neutral and ground bar must be bonded; when a four-wire feed is used, the neutral and ground bars must not be bonded.

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Just found this post on another forum. The detached shop does have water and sewer run but it is not connected at either end. It looks like his setup was code compliant at the time. However by adding low voltage runs or if I wanted to hookup the water line I would be in violation. Additionally the meter is 200A rated and both panels have 200A main breakers. Potentially I could burn up the meter and feeder from transformer if the buildings exceeded 200A.
 
It looks like the answer is to rerun the line between the buildings. At this point I'll need to hire an electrician to pull the meter and disconnect the shop. Then I can add a 125A breaker to the house panel and feed the detached shop panel from that. Am I okay leaving the 200A main breaker in the shop panel as the 125A breaker feeding it will protect the wiring? This should also simplify adding a whole house generator and transfer switch down the road.

I have not read this entire thread so excuse me if I am repeating something that has already been said....
 
the electrical service should only have the neutral and ground connected to each other at one point in the entire system...period. If you connect the neutral and ground together at both the main panel and at the detached building then they in effect become one single conductor and you defeat the purpose of the ground wire altogether.
 
You need to connect the ground in the main house panel to the ground in the detached sub-panel. You also need to drive a ground stake at the detached building and attach all of the device grounds in the detached building to it. Do not connect the ground and neutral together at the detached sub-panel. The neutral and ground should only ever be attached together at one point in the entire system and that is normally at the main panel in the house assuming your house is to code.
 
Mike.

mikefamig said:

I have not read this entire thread so excuse me if I am repeating something that has already been said....
 
the electrical service should only have the neutral and ground connected to each other at one point in the entire system...period. If you connect the neutral and ground together at both the main panel and at the detached building then they in effect become one single conductor and you defeat the purpose of the ground wire altogether.

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Not a problem. You missed the issue that I only have 3 conductors between the buildings. From reading NEC code as long as I don't want low voltage or water in the shop the existing install is grandfathered in. Since I want to add low voltage I need to rerun a new cable with 4 conductors to the building. This unfortunately is not the answering I was looking for. The current cable is 4/0 aluminum direct burial 3' deep in a sand bed. I haven't moved in yet, but the owner mentioned there are two unused conduits. I'm hoping they are sized appropriately and still intact 20 years later so I can use this to pull the new run.
 
This other site I found confirms it as well and has diagrams detailing proper installation although it is for NEC 2002. http://www.selfhelpandmore.com/home-wiring-usa/accessory-structures-to-dwellings/wiring-a-detached-garage-2002.php

Let me start by saying that I am not a licensed electrician and welcome criticism. If you are not completely comfortable with the wiring plan then definitely consult an electrician.
 
Sorry I overlooked some of your original question. I posted the points that I made about the ground as a point of safety and just wanted to get it out there and didn't address your question directly.
 
With three conductors you currently have line1, line2 and ground, no neutral. Line1 and line2 are used together to supply 240 volts and the ground is part of the bonding grid required by code. This is to code because you do have the ground acting as a bond to earth to safely collect any stray current  that may occur. If you decide to add a fourth conductor then just do not connect the neutral and ground together at the detached building. The sub-panel and all outlets should be connected to the ground from the house and also to a stake or two in the ground at the detached building. I have had people disagree with me on this and there seemed to be some confusion about it among people that I talked to so I did some reading and spoke to an electrician until I understood the purpose of each wire and understood the purpose of a bonding grid and how it works. The neutral lead carries current under normal operating conditions and the ground does not. The ground wire is there to carry stray current safely to the earth when there is a problem.
 
I just was trying to make it clear that the ground should be attached to the neutral as near the source as possible which is the main panel in my house. At no other point in the system should the neutral and ground connect to each other.
 
Mike.

rsw686 said:

The issue with my setup is there is no ground wire between the structures. The neutral and ground bus bars are bonded and ground rods are connected to the ground bus bar in both buildings. The previous owner built the shop back in the 90s so it has been setup this way for 20 years. He only has power to the shop and no low voltage runs or equipment. Although looking at this another way maybe there is no issue as with the neutral and ground bonded at both buildings the neutral wire between the buildings essentially becomes a ground tie as well.

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It appears to me that your neutral and ground wire are one and the same no matter what name you give the wire.
 
If you connect a 120 volt load to the circuit in the garage then you are using the third wire as a neutral and you have no bonding system. If you only connect 240 volt loads in the garage then the third wire can be used as an earth bond.
 
Mike.

I disagree with Mike on the conductors. The OP stated

The house and shop only have 2 hots and a neutral running to the panel. Both panels are treated as main panels and the buildings each have their own ground rods driven.

Other than that small point I agree with Mike 100%. Ground wires between buildings should not be run. An out building is not a subpanel in the same building. One point  bonding as the ground system should NOT share neutral currents.
 
The only thing you should have to do it remove the bonding screw in the out building. That should disconnect the grounding system for that building from the neutral.
 
The only problem with this is your service is split into two buildings and I have forgotten what the CEC says about bonding that building ground system to the neutral as it is not a subpanel and it is the entrance point.
 
If you are having further inspections your Inspector can tell you his preferences and/or state the code. Put the screw in or remove it and live with it but my guess is the ground wire between buildings will have to go. The inspector may not like it hanging around and make you snip it off back at the jacket, at both ends, so it can never be used, or in the worst case make you run  anew cable without one.

LarrylLix said:

I disagree with Mike on the conductors. The OP stated

The house and shop only have 2 hots and a neutral running to the panel. Both panels are treated as main panels and the buildings each have their own ground rods driven.

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LarryILix
 
I think that much of the confusion that I faced in learning to wire my detached building was in distinguishing between a ground/earth and a neutral. In this case with three conductors we agree that two of them are line voltage and in my mind the third is either a ground or a neutral depending on what it is connected to in the detached building.
 
If the building has only 240 volt loads then the third conductor can be considered and used as a ground but if the building also  needs a 120 volt supply then the third conductor will be used as a neutral for that purpose and the system is lacking a ground conductor.
 
Mike.

I'm interested to know from the OP
 
When you say that the detached building is connected directly to the meter do you mean before the meter of after the meter? Just curious.

You should not have 2 points of ground on the same conducting body of wire/other conductor.
 
If you were to put a ground in your out-building, then you need to NOT tie it to neutral at the out building and you need to NOT connect it to ground from the other structure.  You also need to ensure it is actually a ground since it will be your only ground for that structure and it will be a safety issue.  Soil types and moisture and such will affect this.  Realize that an appliance could (improperly) have a connection between ground and neutral.  So you take a risk that plugging something in might tie your neutral and ground together and foil your efforts to keep them separate.
 
In summary, the same conductor can not be connected to Earth in 2 different places where anything else lives between them.  The potential charge of Earth will at times be different between the 2 points and you will then get current which very well may severely damage anything in between.  Imagine a lightening strikes a tree 100 feet from your house.  The one grounding point might be 100 feet away, the other is maybe 200 feet away.  The Earth 100 feet away may have a greater charge than 200 feet away, the electrons will flow from the one ground to the other and destroy stuff along the way.
 
If at all possible, I would connect the two buildings with all legs of service, (2 legs of hot, neutral, and ground).  If you are only needing 240 service, then you can drop the neutral, and if you are only needing 120 then you can drop one leg of hot.  And make sure your neutral and ground wires are properly insulated as they travel between the buildings.
 
As far as connecting the buildings with data, fiber is a very good way to prevent issues. 

Lou Apo said:

You should not have 2 points of ground on the same conducting body of wire/other conductor.
 
If you were to put a ground in your out-building, then you need to NOT tie it to neutral at the out building

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Agreed, the neutral should have only one point of earth ground.
 

Lou Apo said:

and you need to NOT connect it to ground from the other structure. 

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I don't understand this. I say tie all grounds together between buildings and have as many earth grounds as you have the energy to drive stakes into the earth.Why would you try to isolate the grounds between the buildings? Bond it all together and isolate the neutral. no? All grounds in each building go to earth via the shortest possible path and neutral floats until there is a fault.
 
I understand that the earth is not a dependable conductor between buildings which is why I have a ground conductor between the buildings and earth grounds at each building. One big bonding grid.
 
Mike.

Lou
 
I was just thinking more about what you said about the lightning strike in the earth having different potential at each of the building's ground rods. All that I can conclude is that it would not matter as long as the line and neutral are properly isolated from the earth ground then the lightning would go harmlessly into the earth in the end. Please feel free to correct my thinking here, I'm always looking to learn.
 
Mike.

mikefamig said:

Lou
 
I was just thinking more about what you said about the lightning strike in the earth having different potential at each of the building's ground rods. All that I can conclude is that it would not matter as long as the line and neutral are properly isolated from the earth ground then the lightning would go harmlessly into the earth in the end. Please feel free to correct my thinking here, I'm always looking to learn.
 
Mike.

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Yes, it may harmlessly travel from one ground rod through ground wire and out the other and your none the wiser.  But you really don't want any current on a ground wire in your house.  Current means potential and potential can arc inside of your electronics where your ground comes near other conductors.  High voltage lightening stuff will sometimes surprise you when it finds its path of least resistance.  
 
Their are basically two ways to ground a building.  Insulate everything from Earth except one spot (the usual approach).  The other is take the extreme opposite approach and ground like crazy.  In other words, make the entire strcture into a single grounding rod.  This basically means you spike grounds every couple feet around the entire structure and tie them all to each other and to the structure all along the way.  The second approach is the high end approach, it is very expensive, but very effective.  Basically you turn your entire structure into a Faraday cage and then make the entire bottom half of that cage a single gigantic ground point.  This would be done for a highly sensitive, high priced set of equipment.