Detached garage grounding
- Thread starter rsw686
- Start date
apostolakisl
Senior Member
rsw686 said:I've read over the NEC code and it clearly states that both builds must have a ground rod driven. I found an IAEI post, which has pictures showing my current setup per NEC 2005 code. The catch is there can be no other metallic paths between the buildings. I could run fiber for network, but that leaves me stuck on the security side. I could forgo the OmniPro expansion enclosure and just home run a few zones, but I feel like I am fighting the inevitable.
It looks like the best/correct answer, which is what NEC 2008 requires, is to just run a new feeder with 4 conductors. I'm going to follow NEC code and leave the ground rod connected at the shop. I also will need to rewire the shop panel so the neutral and grounds are separated.
After looking at the below picture it makes sense that with 3 conductors between the buildings ethernet, security cable, etc would become a potential source for stray current to destroy the equipment. It just doesn't seem worth the risk to fry equipment over a few hundred dollars of cable. Since I do have a disconnect at the house for the shop feeder I can abandon the 4/0 3 conductor cable, install a new 125A breaker, run 1/0 aluminum 4 conductor cable, and hookup the shop panel myself. After that is working I can pay an electrician to pull the meter, remove the splice box and fused disconnect, and connect the house panel directly to the meter.
This hookup is fine until you run other wires between the two buildings. The two grounds are bonded, but that doesn't mean electricity will only follow that path between the two of them. Even though you haven't tied to the neutral to the ground, electricity can still arc the microscopic spaces between neutral and ground in your equipment and use your LV stuff as a parallel path to the ground wire. You can use the surge protectors mentioned and cross your fingers, or you can go fiber.
If your devices are leaking current to earth grounds through their cabinets then I would consider that as a fault in the system that should be corrected. How else can you be sure that there will never be current on a ground if you allow your devices to conduct it there?Lou Apo said:
Also current will take all paths to earth but most of the current will take the path of least resistance to earth. If you have properly driven ground stakes into the earth at each building and connect all equipment grounds to them then any current that leaks into the system in each building will go safely into the earth through those stakes before traveling to the other building.
Mike.
I want to add that I agree with Lou apo that a device can leak current into it's ground. This is why we have the ground/bonding grid in place. It is there by design to conduct any stray current safely into the earth. Part of that plan is to give your equipment the shortest possible path to earth so that it gets there before doing harm.
mikefamig said:
apostolakisl
Senior Member
mikefamig said:
The trouble is you'll never find your "leak" to ground. Lightening strikes generate large voltage potentials and at some point a non-conductor becomes a conductor. It could be an arc through air or some other medium that does not conduct on your testing. When presented with 1000 volts or 10,000 volts, or who knows, suddenly it changes its properties and conducts.
apostolakisl
Senior Member
pete_c said:or is the fiber media converter powered over ethernet?
No. It is just powered at each end. You could probably power each end via POE.
fiberconverters.jpg
That is a nice drawing of the setup. Mine looks just like it. And I suppose you could use POE with a split off, you'll just have to check the current demand of your converter and its voltage. The thing is, both ends require power regardless of whether you use fiber or direct ethernet. it is true that direct ethernet itself requires no power of its own, but whatever it is plugged into still must. So I would suggest powering your fiber/ethernet converters using the same power source as your other stuff since one is not good without the other.
Lou Apo said:
I do understand that what you say is true and technically there is no way to protect from that sort of thing as long as you have outside wires in the ground but that doesn't mean that I shouldn't try.
I don't know if fiber optic is capable of replacing all of the conductors between my buildings.
If I was to try to remove all buried cable I would have to replace my elk data bus and ethernet cat6 cables with fiber and that still leaves me with an 18awg cable that carries power from the house to elk input and output expanders and a second 18awg pair that carries audio from the elk to the speakers in the garage. I could eliminate the power cable by installing a power supply in the garage but I already have a 6 amp supply in the house and it seems to make sense to use that rather than add another power supply in the garage. I do not know how I would get the audio from the elk panel in the house to the garage unless you can transmit an analog audio signal over the fiber. Can you?
Surge protectors seem like a good idea in my situation. Mike.
Lou ApoLou Apo said:
another question -
If lightning strikes the ground why would it travel into the building on it's earth lead to a piece of equipment and conduct current to the neutral in that device if that neutral is isolated from earth? I'm a little confused here. I can see the lightning traveling in on a data line and finding an earth ground but not traveling in on a ground wire and finding a neutral.
Mike.
You neutral may be bonded to the ground wire before the lightning gets to the ground to be absorbed. All conductors have some impedance to them, especially when passing through metallic holes and/or having slack take-up loops in them.
Lightning is composed of many high frequency bursts that don't necessarily follow conductors. Even sharp bends in the conductor can cause it to take another path. High frequency corona, skin effect, antenna, and many other phenomenon principles apply.
Lightning is composed of many high frequency bursts that don't necessarily follow conductors. Even sharp bends in the conductor can cause it to take another path. High frequency corona, skin effect, antenna, and many other phenomenon principles apply.
apostolakisl
Senior Member
Like Larry said. I honestly do not pretend to even come close to understanding all the nuances of the behavior of lightening. Just look at pictures of a bolt of lightening and ask yourself "how did that crazy pattern turn out to be the path of least resistance?" Now you get it, right?
You really can't give lightening any reasonable path that includes your stuff.
It might be possible to keep all of the stuff in bldg2 as if it were still in bldg 1. In other words, keep it absolutely separate from the bldg 2 electrical system. It can't have anything to do with the ground, hots, or neutrals in bldg 2, not even close. If it is all 100% powered from bldg one and you don't accidentally get it anywhere near ground in bldg 2 or connect any of it to anything that is connected to the power system in bldg2 then you would seem to be relatively safe. You would want to use shielded wire and ground it bldg 1 to help with induced voltages. In this sort of way, it would be like running stuff to an out building that doesn't have an electrical system at all.
The simplest of these would be the speaker. I would have my doubts about running door contactors and stuff like that though that might be connected to an Elk expansion board. Perhaps if it is all wood construction this stuff can stay clear of bldg 2 conductors. Your internet is going to be very hard. That means powering any switches, routers, computers, whatever else, that the internet is doing in bldg 2 using only bldg 1 power or batteries (ie laptop).
You really can't give lightening any reasonable path that includes your stuff.
It might be possible to keep all of the stuff in bldg2 as if it were still in bldg 1. In other words, keep it absolutely separate from the bldg 2 electrical system. It can't have anything to do with the ground, hots, or neutrals in bldg 2, not even close. If it is all 100% powered from bldg one and you don't accidentally get it anywhere near ground in bldg 2 or connect any of it to anything that is connected to the power system in bldg2 then you would seem to be relatively safe. You would want to use shielded wire and ground it bldg 1 to help with induced voltages. In this sort of way, it would be like running stuff to an out building that doesn't have an electrical system at all.
The simplest of these would be the speaker. I would have my doubts about running door contactors and stuff like that though that might be connected to an Elk expansion board. Perhaps if it is all wood construction this stuff can stay clear of bldg 2 conductors. Your internet is going to be very hard. That means powering any switches, routers, computers, whatever else, that the internet is doing in bldg 2 using only bldg 1 power or batteries (ie laptop).
