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  #1   IP: 192.55.52.4
Old November 20th, 2006, 01:51 PM
Sertain Sertain is offline
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Exclamation Running power to an unattached garage

First time poster here looking for some advice.

I recently built a 2 story garage with dwelling space upstairs. With the number of circuits I plan to have upstairs and downstairs in the garage, I believe I need a 125Amp panel in the building. I'll need 240V for the HVAC unit.

I'll be running the feeder from my main 200A panel at my house.
The 200A panel is approx 160ft away from the garage. 90ft of it would be under the house.

I just dug the ditch from the house to the garage, and it's about 24" deep (from what I understand, the requirement is 18" of coverage, and I plan to put in 2" Cat40 electrical PVC to make it easy to pull the wire through the 70ft of trench).

Couple of questions -
1 - What gauge wire do I need to run to the panel - I'd assume i'd need two hots and a neutral (I have a ufer?? ground in the pad, so I shouldn't need a 4th wire). I was thinking that I need around #2, but maybe 1/0??

2 - Can I use the same wire (contigeously) from the box, under the house, and into the PVC in the trench, all the way to the building, or does there need to be a different type of wire under the house than what is in the buried PVC?

3 - When I go from the external main 200A panel, to under the house and then out of the house again, do i need break-in and break-out boxes? and if so, does the wire actually have to be spliced in there? or can I just leave a loop for future accessibility? It makes sense I would need a break-in box but doesn't make sense that I need to cut the line just for the box.

:
Any help would be great!


p.s. I also have a water line that I also need to run the same way, it would be PVC and am curious if it's legal to put in in the same ditch, especially if it's only 24" deep but obviously would be easier to not have to dig another ditch if possible....guess the California (Eldorado County code would be the question? and the seperation requirement / min depths of water & or electric.

Thanks again
-Sertain
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  #2   IP: 24.36.89.247
Old November 20th, 2006, 02:35 PM
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joed joed is offline
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If you have any other metal (water pipe, phone wire, cable wire) running between the house and the garage you need the fourth wire.
In order use the same wire all the way you will need conduit inside the house as well. You can loop the wire through any J-boxes without connections.
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  #3   IP: 192.55.52.4
Old November 20th, 2006, 03:07 PM
Sertain Sertain is offline
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Default so

So, I only need to add a ground if I plan on adding some additional cables in the same PVC Tube? i.e. want to add a Cat5-RJ45 line in there also?

Since it's low voltage, coudn't it just be dropped in another tube in the same ditch without restrictions?

If the water line is in PVC, seperated by 6", does that count? or only it's only a problem if the water line is a metal line? ie. copper or such.

And if I didnt use the same 2" piping under the house, what type of cable is it? I wasn't planning on using direct burial in the PVC line, just standard Non-metalic copper?


-Sert
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  #4   IP: 24.16.225.236
Old November 20th, 2006, 04:50 PM
suemarkp suemarkp is offline
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The 3-wire -vs- 4-wire feeder depends on if you have any grounded metal paths between the buildings. If you do, that metal path will end up paralleling the neutral and could potentially burn up a smaller wire (like a CATV shield wire), or put current or sparks where you don't want them (gas line, or unsuspecting plumber cuts the water pipe and gets shocked).

To be safe, and allow future metal paths, I'd run three #2 copper wires (or maybe even 1/0 because of the distance) and a #6 copper grounding wire. At the detached building, keep the neutral bus insulated from the panel and don't use the green bonding screw. The white wires go on this bus. Buy an accessory grounding bar for your panel if it doesn't have separate neutral and ground bars. Put the #6 ground on that grounding bar, along with all the bare branch circuit grounds, and the wire to your ground electrode (that UFER wire must be #8 or larger copper). This bar must make a good electrical connection to the panel chassis.

There is no requirement for a break out box, but you will need a disconnect near the point of entry of the wiring into the detached building. A main breaker panel qualifies if you keep the cable distance short from outside to inside (tyipcally 5 feet or less). LB fittings are typically used to may a 90 degree transition from in-wall to down along the wall and into the dirt. These have removable covers to aid in pulling the wire through.

You must use a wire rated for wet locations when it is underground (conduit or direct buried). Individual THWN wires are what is normally used, but these must be run in conduit completely and not run through walls or otherwise exposed. You can use flex metal conduit in the house if that helps get the conduit all the way to your panel. Or you could use NM or SER cable inside and UF or USE outside, but you'll have to splice those together, and you need a rather large box to do that (I doubt you can splice that in a 2" LB fitting). The only cable you could run the whole way and not have to use conduit is UF cable.

Putting water pipes in the same trench as power usually isn't a problem (at least in the NEC, local rules may differ). Your phone line, however, must use a separate conduit or just be direct buried at least 2" from the power wires. Low voltage wires and higher voltage can't be in the same box or conduit without a barrier.

Finally, make sure you can get a 125A double pole breaker for your existing home panel. It may cost you $50 or more. I'd also recommend a main breaker type panel at the detached building.
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  #5   IP: 192.55.52.4
Old November 21st, 2006, 08:20 AM
Sertain Sertain is offline
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Default Future Metal Path

I guess I'm a little ignorant about this but what exactly classifies for a 'Future Metal Path'.


Are you saying, that maybe in the future, a copper line may intersect that 2" PVC within 6" and thus be considered a metal path? or are you saying that the wire coming into the breakout box may be near a metal connection (like a metal box) and thus require it?

I do have some extra #6 anyway, so it probably isn't a big deal to just drop it in the channel, though 3-1/0's and a #6 may start to get tight on pulling it through the 2"??

Thanks again for all your support.
Guess I'll go check the prices of UF vs the others to see how much more expensive it will be to run UF the entire way (last time I checked it was a bit more expensive).
-Sert
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  #6   IP: 130.76.32.167
Old November 21st, 2006, 01:19 PM
suemarkp suemarkp is offline
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What I meant by future metal path is this:

You can not have a 3-wire feeder if there is a continuous metal pathway between the source and destination buildings and that metal path is grounded at each end. Installing a 3-wire feeder now will not permit this type of pathway to be installed at a later date (unless you also change the subpanel bonding and run the 4th wire when the metal path is installed).

A CATV cable is required to be grounded at each building, so this would be a grounded metal pathway. A phone line is not grounded nor is an ethernet cat-5, so that would be OK. Metal piping and conduit is required to be bonded to the service in each building, so that would be a grounded metal pathway unless some non-metallic section was installed in the earth between the buildings. A metal fence is OK, because it is not required to be bonded to any building. But if you ended up doing that (by mounting grounded equipment on it from each building), it would become a metal pathway.

These pathways have nothing to do with proximity to your conduit or panels. It is the creation of a parallel neutral that the code does not want. Having a conductor (e.g. continuous metal pathway) that is connected to "ground" at each building will be paralleling the neutral in 3-wire systems.
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  #7   IP: 192.55.52.4
Old November 21st, 2006, 03:46 PM
Sertain Sertain is offline
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So does this metal pathway have any distance limits? If I am following you correctly, if any grounded path ever crosses over a buried non-grounded power line, it has a problem, irrespective if it is 6" or 36" away?

I could see if you wanted to put a grounded CATV cable in the same PVC pipe as the runner, that this would be a problem, but it seems like you are saying that the grounded CATV cable can be 12" above it and run perpendicular to the power and that would be a problem because the neutral (non-grounded) power runner would essentially sense the ground and possibly arc?

-Sert
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  #8   IP: 24.16.225.236
Old November 21st, 2006, 04:25 PM
suemarkp suemarkp is offline
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You're still not getting it. It has nothing to do with distance to the buried feeder. This metal pathway can be long and take a totally different path from the buried feeder. It is the fact that some wire gets connected to the grounding system at each building which causes the problem. When I say it parallels the neutral, this is not a proximity or layout issue, this means that a conductor (metal path) has been electrically put in parallel with your service neutral to the building.

Maybe this will help. With a 3-wire feeder, the neutral in that feeder must be bonded to the ground bus in the remote building panel. In the main building, the main electrical service has the neutral and grounding on the same bus bar. So if a wire is run between the main building and the remote building, and each end goes to the neutral bus bar in its respective panel, you now have a parallel path for the neutral between the buildings. A CATV cable is required to be grounded when it enters your house, and it is shielded coax so the shield is effectively grounded in every piece of coax. Extend one of those to the remote building, and you're required to bond/ground that coax to the remote building ground system. In a 3-wire system, neutral and ground use the same bus bar so now you have the parallel path. If the ground bar was electrically isolated from the neutral in the remote building, then the coax cable at the remote building is still at the same voltage as the main building (which is what we want).

Perhaps its the confusion between bonding and grounding in the NEC. None of this has anything to do with earthing, it is really the fact that a conductor is bonded at both buildings to the neutral bus. It just so happens in 3-wire services that the neutral, ground, and bonding busses are one and the same. Having the 4th wire allows grounding/bonding to be one bus and the neutral to be an electrically separate one. All neutrals and grounds and bonded together at one point (the main service disconnect from the power utility), and things work best when that is the only place this occurs. With 3-wire feeders to remote buildings, this rebonding of neutral and ground happens again which can create dangerous current pathways when things get grounded from both ends.
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  #9   IP: 192.55.52.4
Old November 21st, 2006, 05:22 PM
Sertain Sertain is offline
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Default ohhh.

Seems like connecting (bonding) the two (ground and neutral) should only happen at the main panel, and after that, they should always be kept separate?

Basically, you want to make sure the ground plane is contiguous and not two independent ground planes bridged by a neutral?

If that is the case, why would you ever want to not run a ground? It would seem like it would break the rule of bonding the neutral/ground at any other location than the main and would cause the discontinuity between the ground planes.

And the ufer at the new building is just another ground earthing point to help stabilize the ground but not much else?

-Sert
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  #10   IP: 24.16.225.236
Old November 21st, 2006, 06:19 PM
suemarkp suemarkp is offline
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Now you've got it. The reason 3-wire services are allowed is that is how your house is done. There are people that think this is bad and would like the power company to run 4 wires from the transformer to your house instead of only 3.

But there is so much of a history of 3-wire services that this will be hard to change. And the "bad" things that can happen between your house and an outbuilding can happen between you and your neighbor if you are connected to a common CATV system or an all metal water distribution system. With this history, professionals have learned where to be careful, and there really aren't many problems considering that there are millions of homes. This also can cause a lot of "stray voltage" because neutrals have voltage drop so there ends up being a bunch of small voltage power sources plugged into the earther everywhere (every ground rod).

Here in Washington state, you must run all feeders as 4-wire. The NEC allows 3 to a detached structure when there are no grounded metal paths, but Washington has nixed that section state wide.

The main reason for a ground electrode system at each building is more for lightning protection than anything else (a shorter path to shunt it instead of going all the way back to the main house ground rod). Not many things care whether the voltage to the earth is different by a few volts at given spot of earth. Move 3 or 4 feet in the dirt and the voltage changes anyway.
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