In-laws want me to run power out to their detached garage. FIL has plans to turn it into his own “sports pub” at home, with Dish TV and a “kegerator”, so I want to make this happen!
The garage was recently built by the previous owner with conduit running to it from the main panel. There is rebar extending out of the sill plate. I know that sub-panels now require 4 wires: 2 hots, one neutral, and one ground. and that the neutral and grounding buses are independent in the sub-panel. BUT, does the sub need to a have a ground from the main if I ground to the rebar?
If yes, should I still ground to rebar?
Can I run NM feeder wire (say, 4 gauge) in conduit or do I need THHN/THWN?
Lastly, there is but the one conduit. Can I run TV cable (sorry not sure of the proper terminology) in the conduit with the electrical?
All guidance is appreciated. Thanks
Replies
"BUT, does the sub need to a have a ground from the main if I ground to the rebar?"
Yes, if there are any metalic paths back to the house. That includes phone, cable, water pipes. And even if they don't exists now it sounds like they might in the future so go ahead and run the ground wire.
"If yes, should I still ground to rebar?"
Yes, you still need a local grounding electrode.
Can I run NM feeder wire (say, 4 gauge) in conduit or do I need THHN/THWN?
I doubt that you could even pull #4 NM (or SE, don' thing that NM is availabe that big).
But in any case I am assuming that this is underground conduit. Tha tis a "wet" area and NM does not qualify, nor does SE. But there is UF and USE that would. But again you don't want to full that.
Use THWN (the W is wet qualified).
Can I run TV cable (sorry not sure of the proper terminology) in the conduit with the electrical?
No
Thanks for the information, Bill - very helpful. So helpful, in fact, that I'm reduced to a single follow up question:
I <still need a local grounding electrode>? Does this mean the grounding bus bar in the sub is grounded back to the main and to the stubbed rebar below the sub? I'm not clear on what I might be grounding "locally" if I have a ground that runs back to the main's gounding bus/ground rod.
Then again, the efficacy of this rebar is dependent on it being not just a stub, but part of system that is at least 20' long and under the required depth of concrete (I didn't build the garage).
Thanks again
if the garage is attached, you do not ground to rebar, four wired to main. If the garage is not touching main house in any way then four wired to main and connection to rebar
I'm certainly not a pro electrician, but -
I can't imagine that grounding to rebar would be acceptable. The rebar just goes down into the concrete. A ground rod would have to be down in the dirt 8' or so.
Or did I miss something?The best way to escape from a problem is to solve it.
FWIW, there is one type of acceptable "grounding electrode system" (I think it's called a "Ufer ground") where the grounding electrode is clamped to rebar in the footer - the rebar has to be at least 20' long and at least 1/2".
I've heard some areas allow rebar for a "driven grounding rod" others require copper. Galvanized pipe used to be used but so far as I know is no longer accepted anywhere.
_______________________
Tool Donations Sought
I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
Boss
Bob is right (for once<G>). It is called a Ufer ground and I have heard that in some local codes/inspectors are now requiring it as the primary ground.
The code (99) talks about "Grounding Electrodes" and "Made and Other Electrodes". Not sure of why the differnece, but more weight is given to the grounding electrodes.
Grounding Electrodes can be,
Metal water pipe within 5ft of where it enters the building. It must be contious (electrically) for at least 10ft and in continous contact with the ground. If a metal water pipe is used then a supplemental electrode is required.
"Metal frame of the Building or Structure. The metal frame of the building or structure, where EFFECTELY GROUNDED". Emphasis added. There is no other explanation of what effectely grounded is.
Concrete encased electrode. Must be enclosed with at least 2" of concrete and located in in/near the bottom of a concrtete foundation or footing that is in direct conwith the earth. It requires at least 20 ft of rebar that is "connected". Ordinary rebar twist ties can be used for the connections.
The large surface area of the concrete and concrete affinite for mositure makes it a very good ground.
A ground ring. The building is encircled with a bare copper wire at least 2.5 ft deep.
If none of the aboved are used then a made electrode is used. Made electrodes require a supplemental electrode unless it is tested and founded to be below 25 ohms resistane.
Made electrodes include;
Local metal undeground systems (piping and/or tanks), except gas piping. But the gas piping is still bonded to the grounding system.
Rods and Pipes. A large number of different pipes and rods can be used as long as they at least 8 ft long. That include conduit, pipe, and rods of iron, steel, stainless, and copper. There are a lot more details of the size and treatments.
A metal plate with at least 2 sq ft of surface incontact with the ground.
Thanks for the info, guys.
I had never heard of using rebar for a ground. Seems to me it wouldn't be wise to do so, as you never know how much rebar you're actually hooking up to. (Unless you installed the rebar yourself)This is the time of year when there are a lot of commencement speeches in the air. And there's a lot of air in the commencement speeches.
I think I read somewhere that Ufer grounds were developed by the Army where there is, presumably, central control of building projects.
_______________________
Tool Donations Sought
I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
According to the electrical inspector in the area where I am planning on building, in this county, grounding to rebar in a footing is the preferred method of grounding.
"I <still need a local grounding electrode>? Does this mean the grounding bus bar in the sub is grounded back to the main and to the stubbed rebar below the sub? I'm not clear on what I might be grounding "locally" if I have a ground that runs back to the main's gounding bus/ground rod."
I am not sure of all the reasoning, but there 3 different purposes for grounding "systems". Maybe 4lorn1 will see this and have some more specific information.
1) a discharge path for "external" voltages. This includes ligthning, voltages induced by nearby ligthning, and static buildups.
2) A safe path for any fault currents that will cause the CB to trip. This is mostly what the equipment grounding part of the system (the ground pin on the receptacle/plug and associated wiring).
3) bonding so that any conductive surfaces in the structure will be at the same voltage.
Now #1 requires an "earth ground". My SPECULATION is that the ground back to the house is not concidered as adequate because unknown runs and the possilbility that it will have too high impedence to the very high frequency signals that lightning strikes generates.
For #3 if you have any current flowing through a conductor you have a voltage drop. Thus the system is setup so that the grounding system will never have any current flowing through except during fault conditions. That is why sub-pannels within the same structure are required to have an isolated ground wire and the neutral bus bar is isolated.
Then all water pipes, gas pipes, and metal furnace ducts are "bonded" to the ground system and at the same voltage. Particularlary importand for any spa's or pool's that require things like metal ladders to also be bonded.
Now there are exceptions that treat pannels the same as the main entrance at the home. IE; 3 wire connections to the "power source" and full local grounding systems.
But you have a metalic path back to the house in your case. In that case the metalic path will be referenced back to the main house and thus might have a voltage difference between that equipment and equipment bonded to the garage ground. Also if the path is telephone/cable then you might end of with stray currents flowing through the cable which can affect the operations of the electronics.
So in your case you need the 4th ground wire from the house. It has to be connected to ground bus on the pannel along with the local ground electrode (concrete rebar in your case). And the neutral bus bar will be isolated from the pannel case. That requires removing the bonding screw or strap. In some cases there will be a separate ground bus bar in the pannel and in other you will need to by a separate ground bus kit.
Bill,
To you and the others I say thanks. Your answers were very helpful. I did know the code for GEC regarding the rebar - just have to assume it's at least 20'.
Out of curiousity, grounding the sub to to rebar as well as back to main panel, doesn't that bond the main to rebar in the detached garage? Then, both the panels share the two grounds. Is that the NEC's goal here? So that separate structures sharing a common power source (off the elec. comp. transformer) are bonded together and at the same fault potential?
"Then, both the panels share the two grounds. Is that the NEC's goal here? So that separate structures sharing a common power source (off the elec. comp. transformer) are bonded together and at the same fault potential?"
That is my take on it.