I am building a detatched garage about 75 feet from my attached garage. I have my main panel and a sub panel beside each other in my attached garage. The sub panel only has my small upstairs heat pump/ air conditioner for a bonus room hooked to it as well as a 50 amp plug for a small welder I almost never use. Can I run a sub panel in my new detached garage/workshop from the sub panel in my current attached garage?
If so, do I need another ground rod at the detached garage?
If it helps, I can remove the 50 amp welding plug because I only plan to wel in the detached garage anyway.
I have 200 amp service in my main panel. I think the sub panel next to it I bought was either a 50 or 100 amp panel but like I sais, the only thing on it is the 1.5 ton heat pump. It is usually turned off as the upstairs is a play room for the kids.
I added the sub panel because all of the breakers in my main pannel were almost full.
Yes you can run from your existing subpanel to feed the unattached garage. Yes you need to install a ground rod at the panel in the unattached garage (NEC article 250.32). You also do need to run a ground conductor between the panels. (If you were only running a single or multi-wire branch circuit to the unattached garage, you would not need the ground rod.) Keep in mind that in both subpanels, the neutral cannot be bonded to the metal enclosure, or any of the ground conductors.
If my main service is 200 amps. An the attached garage aub panel is
100 amps, can I put an additional 100 amp sub panel in the detached garage?
In my exisiting sub panel, I think the netral goes to the neutral bus in the main panel and the gorund goes to the ground in the main panel. Is this correct?
My wire will be coming underground through a 90 degree piece of conduit that will be put in before the concrete is poured. What is the best way to run the ground rod in this instance?
If my main service is 200 amps. An the attached garage aub panel is
100 amps, can I put an additional 100 amp sub panel in the detached garage?
In my exisiting sub panel, I think the netral goes to the neutral bus in the main panel and the gorund goes to the ground in the main panel. Is this correct?
My wire will be coming underground through a 90 degree piece of conduit that will be put in before the concrete is poured. What is the best way to run the ground rod in this instance?
Assuming you are protecting the feeders of each of these subpanels with a
100 amp 2 pole breaker then yes, you can make the 2nd subpanel a 100 amp one. If however, you've tapped off the incoming mains to feed the attached garage subpanel, then no, you cannot install a 100 amp subpanel in the new garage. The reason being that in the 2nd scenario there would be the potential to overload the unprotected 200 amp main feeders.
The neutral and ground wiring of your existing subpanel sound correct.
It's best to install the ground rod outside the building and run the #8 ground wire from the buried ground rod up through a short piece of conduit and into the building. I've seen people drive the ground rods inside then pour the slab over it. They always end up abandoning it and installing a second one outside after the inspector come to inspect and cannot see it. LOL
Food for thought...install a pair of 3/4" conduits along side the feeders going out to the new building. These are great for installing 3-way switch circuits for outside flood lights, phone or intercom wires, or garage door opener pushbuttons in the house.
Both sub panels will have a 100 amp breaker inside the panel. No panels will be runnign off the mains entering the house.
Not sure exactly what you mean by installing 3/4 conduit along the "side feeders". What are you callign side feeders? (Forgive my ignorance!)
I dont know if it matters but this buildign will have metal siding. (Like a pole barn). So I would drive the ground rod in the ground run the wire into conduit up the side of the metal and cut a hole in the metal for the wire to enter into the sub panel of the detached building?
It is not allowed in the slab. A concrete encased electrode is supposed to go in the base/bottom of a foundation or in the footing. I believe the reason for this is that if you put it in the slab, there is not enough moisture present to allow conductivity from earth through the concrete and onto the rod/wire.
That's not what I wrote...now is it!? :) I wrote, "along side the feeders" I did not write, "along the side feeders".
Feeders are the conductors (mains) feeding the panel with power. All I was trying to say is to run the pair of 3/4" conduits in the same trench with the feeders out to the new unattached garage.
No it doesn't matter that it's a metal sided building, you still ground the panel the same way. Yes, drive the ground rod below grade, clamp the ground wire to it. (Do not bury anything until it's been inspected.) Run the ground wire through a small trench over to the building. Come up the side of the building with conduit with an LB at the top. Penetrate the building and get the ground wire into the panel. If the siding overhangs the slab by an inch or more, you can come straight up into the bottom of the wall as well.
You should check with your local electrical inspector. People here can give you advice based on the national code, but there are local codes as well. Something that is perfectly legal in one region or town may not be allowed in another.
It depends on the elevation ASL. Once you get above 13 feet most houses are monoslab. They usually just mound up dirt to get there. Look at the new housing developments and all the houses are up on berms with lakes between them.
The concrete guy is installing a 2 1/2 inch 90 degree elbow in the concrete for me to run the wire into the building up through. This will be connected to conduit in a trech goign to the subpanel in my garage. Can I drive the ground rod at the new building and run the ground wire somewhow into this elbow or is that not allowed?
Also, in the same trench as the condiut, can I run other wire? (Coaxial cable, door opener, phone, etc?) Also can I run a water line in the same ditch?
No you cannot insert the wire from the ground rod into the 2-1/2" conduit run that the main feeders are in. Perhaps you can hand him a 3/4" sweep (90 degree elbow) and have him install it next to the 2-1/2" one. You can use the 3/4" one as a sleeve and slide the ground wire up through it.
Yes you can use the same trench for additional items such as other conduits and cables, keeping in mind that cables have to be rated for direct burial. If you run a water line I believe it has to be at least 12" away from all of the electrical items. The required depth for the water line might be greater so that it is below the frost line. It's best to check your local codes for that one.
The elbow for your electrical feed and associated stub up should be the same size as your conduit run between the buildings. The elbow should be set so that the depth of the end of the ninety is the intended depth of the conduit run. The top of the conduit run should be at least eighteen inches underground for it's entire length. The best way to assure that it will remain 18 inches underground is to dig the trench so that it will be laying at two feet to the bottom of the conduit.
As to the other wires you would like to run, that is why the other poster suggested that you install two smaller conduits in the trench with the feeder conduit. Best practice is to separate the conduits by six inches or more of earth to avoid problems on the coaxial cable and the telephone lines from a long run of parallel power and lighting conductors. If you are going to direct bury the coaxial or telephone lines then be sure they end up at least six inches away from the electrical conduit. Conduit is better approach because as technology or the way you use it change you can pull in new conductors or media. The conduit for these other services will need to be stubbed up through the concrete footer and slab in advance unless you want to bring them up the outside of the new building. Stubbing them up inside the building makes a much neater job and is far more tamper resistant.
As for the Grounding Electrode System at the detached garage You can have the concrete folks stub up a piece of rebar at the location of the new buildings Building Disconnecting Means to make it available for use as a Concrete Encased Electrode. For that to be effective the piece that is stubbed up must be carefully tied to the rest of the reinforcing steel in the footer and slab so that all of the steel will behave as a single electrode. That is how you get a true Ufer ground. The NEC requires that, as a minimum, the steel that is tied together forms an electrode twenty feet long. The alternative that someone else already suggested of tying twenty feet of number four copper conductor to the reinforcing steel is also acceptable but that conductor should be protected by a PVC conduit were it comes up out of the slab. Best practice is to connect the electrode conductor to it's first rebar bond just beyond the end of the PVC conduit elbow that forms the stub up out of the slab. If you use driven rods as the only grounding electrodes then you must provide witnessed testing for the inspector that a single rod has a resistance to ground of twenty five ohms or less or you must drive a second rod. If you use driven rods the best practice is to drive them through the very bottom of the trench so that they will extend as deeply as possible into permanently moist earth. The NEC requires that the rods be six feet apart. Best practice is to drive them twenty feet apart and use number two copper; rather than the number six copper that the NEC allows; as the Grounding Electrode Conductor to connect them to the Building Disconnecting Means enclosure. The twenty feet of number two copper is the electrical equivalent of the same conductor used as a ground ring around a small shed. That would give you a much better Grounding Electrode System then just two driven rods driven at surface level only six feet apart as the NEC permits. The rods are completely unnecessary if you install a concrete encased electrode as outlined earlier.
If you install water, sewer, or drain lines they will have to be deep enough to comply with the plumbing code and remain at least one foot from the electrical conductors and conduit.
If the concrete got poured before you could make arrangements for a concrete encased electrode you can still install an excellent Grounding Electrode System by installing a ground ring or by installing a number two bare copper conductor in the trench alongside the water line for it's entire length. The bare number two alongside the water line makes as good a Grounding Electrode as would the water line if it were metallic piping. A ground ring is a bare copper conductor of at least number two American Wire Gage that encircles the entire building at a depth of not less then thirty inches. Ground rings are most readily installed after the footer forms are stripped but before the footer trench is back filled. A ground ring can be installed at any time by digging a thirty inch deep trench around the building. You can even rent a trencher that will dig the trench install the ground ring conductor and back fill in one pass.
It is very worth while to run a separate circuit that will control the outside lights, and serve as an emergency circuit to the new building, in a separate conduit while you have the trench open. A four wire circuit will provide emergency power and lights to the new building and control the outside lights at both ends of the path between the two buildings with control of those lights from either end. Given the seventy five feet of run you may want to up size the conductors one size in that circuit. I'm sure that you can imagine how handy it might be to have a few plugs and some lights that still work if you have to work in the garage panel and you want to deenergize it first. Having control, at both buildings, of outside lights that illuminate both ends of the path assures you will never have to walk to either building in complete darkness.
If I can be of more help you are welcome to write to me directly through the address hornetd (at) gmail (dot) com.
-- Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison
1st, thanks so much for your help. You have some excellent ideas! I had a few questions if you can help a lamen like me I appreciate it!
That is an excellent idea to lay a 3/4 conduit elbow next to my service conduit 90. I assume this is to run telephone/coax, etc separate from the service electic wire conduit. I just hope I can do it myself. The concrete guy is pouring tomorrow so I need to see if I can do it tonight.
Also, is an 8 foot ground rod driven into the ground what is required at my sub panel entrance. It would be nice If I could drive that too tonight but am a little afraid I cant get all 8 feet into the ground.
This will be a 30x30 shop. It is a concrete slab with 2x4 walls directly on top of the slap. The conduit and hopefully ground rod will come up through the 2x4 sill on the concrete for connection later after the building is complete. If I do this, can I run the bare ground wire throught the 2x4 wall up to the electical sub panel?
Does the sub banel need to have a ground wire ran through to the main/ sub panel in my current attached garage? Or, does the new driven 8 foot ground rod for this new building suffice for the ground?
I am asusming the neutral and ground bar in the sub panel should be electrically isolated?
I am also bringing up a pvc pipe in the same fashion as the electrical conduit. (For futer water use). Is there a certain distance it should be away from the electrical conduit? (Where they all come out of the ground into the wall?)
Is it better to use direct burried wire or conduit for the service feed?
Lastly, I know everyone said it wa sfine to run my sub panel to my new garage from the sub panel in my old garage. But would it be better to run it from the main panel. (havign both sub panels feed through a direct separate breaker in the main panel?0
You don't have much of a choice there, all 8 feet has to go into the ground. If it helps, you are allowed to drive the rod in up to a 45 degree angle, in the event you are in a rocky area.
Yes, the ground wire does not have to have insulation on it.
Yes, you need to run a ground wire between the two subpanels.
The water pipe has to be at lease 12" away from the electrical conduits.
You have to use conduit. You cannot use cable underground to feed a panel in an unattached building.
Yes, it would be better to come off the main panel instead of the subpanel.
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