Sub panel question

[Marshallcc]

Ok so first let me apologize. I know there are a million threads on this. This is my first ever post on any type of forum so I'm not really sure of posting "rules" when it comes to when it's appropriate to start a new thread

Now for my question and I'll be as specific as I can.

I bought a house with a detached garage. The garage is wired with a 14 gauge romex type wire (white shielding, more round than flat) for basic spiral cfl lights and outlets. From the looks of things, someone ran 10 gauge wire from the house to the garage into a fuse box. The wire was ran overhead and, while the house was vacant, someone cut the wire for scrap I assume. I have a little higher demand from my garage than it is wired for right now.

I have 150 amp service to my house and the breaker that was originally used for the garage run is 40 amp. Giving myself a few (about 8) extra feet of wire, I'll need about 125 feet of wire to run to the garage. I have a 50 amp stick welder that I've used maybe 3 times in the last decade and I want to go to a medium sized compressor (maybe 25 amps) as the one I have now is a little too small but only draws 15 amps.

I have a sub that's rated 50 amps so I am assuming I need a new, larger sub or I need to do away with the welder. I also want to run a router extender for wi-fi in the garage as well as, maybe, cable for a tv and possibly a phone. My phone now runs off my cable router so I may not have to run a wire for that.

So, finally the questions are:

What size sub? What size breaker in the main and what size wire should I run considering the load drop over the 125 ft? I want to bury it and I prefer copper as I don't want to worry about the aluminum oxidizing or becoming loose. I'd like to run 240 in the garage also. How deep do I bury it? Can I run all the low voltage stuff in one conduit? Do I need a designated ground rod for the garage? More than one? How far apart and what size? I live in north-east Ohio. Should I run the copper in conduit or, if I get the water rated stuff, is it better to bury it without? I believe conduit is mandatory where the wire enters and leaves the ground. How deep does the conduit have to be in those areas?

I know it's a ton of info/questions and I'm sure I still missed some info. Your patience and answers are appreciated.

Mark

 

[Charles (in GA)]

Standard answer:

Assuming you are in the US. (please go to your Control Panel {CP} in the menu at the top of the screen and edit your profile to include at least your state or province.

Install a 90 amp breaker in your house panel, Run 2-2-2-4 Mobile Home Feeder (direct burial OK) and use at least 2 inch PVC conduit to run from the breaker panel to outside to 24 inch depth with wide sweep 90° elbows. Use PVC all the way if you want, it is cheap and easy. Run PVC from the ground (24" deep) up to the garage panel. Your local authority may require a disconnect outside the garage/shop. It is not code to have it outside otherwise. Install a Main Breaker circuit panel with at least 20 spaces, possibly more, rated at least 100 amps, in the shop/garage. The breaker in the shop is merely a disconnect and doesn't matter that it is greater than the 90 in the house.

Charles

 

[pattenp]

My standard answer is 100A main breaker panel fed with #2-2-2-4 Mobile Home Feeder off of a 90A breaker in the house. 2" conduit buried 18".

The MHF is aluminum and don't be afraid of aluminum because it's not the same as years ago. It works just fine when installed correctly.

Here's one post to read.... http://www.garagejournal.com/forum/showthread.php?t=135154&highlight=sub-panel&page=1

 

[wyliesdiesels]

I agree with Charles and Pattenp.

You will need two 1/2" ground rods spaced 6' apart with one continous bare cu wire clamped to each rod and terminated in the subpanel. Also, the neutral bar needs to be isolated/insulated from the panel enclosure and ground bar!

Yes, the communication cabling can be together in one conduit but MUST be in a different conduit than the electrical!

If u do end up going the direct bury route, make sure to put warning tape(not the yellow caution tape) in the trench above the wire. However conduit is easier!

One thing to keep in mind when asking questions, its easier for us to break things down when u put it in a list and try to go for maybe 5 or so questions per post. This just makes it easier to respond to. Of course u can do whatever u like!

 

[pattenp]

I'am sure wylie meant same trench.

......

Yes, the communication cabling can be together in the same conduit but MUST be in a different conduit than the electrical!

 

[theoldwizard1]

Note that Mobil Home Feeder is for underground installation and must be inside a conduit anywhere it is above ground, including inside buildings. I don't think you can use MHF for aerial applications.

The best solution has been presented to you. (Buried 2-2-2-4 MHF feeder, 90A breaker in the house, 100A sub panel in the garage.) This will give you plenty of room to grow.

If you are trying to save a few bucks, you can keep your current 50A subpanel. Assuming the breaker in the main panel is 50A, 10 gauge is not big enough. You would need #6 copper/#4 aluminum for overhead installation.

Don't worry about running the welder. The duty cycle is low enough that it will not pop the breaker in the house.

If you are going to get rid of the welder, you could go with 10 gauge copper and a 30A breaker in the main and be just above 3% voltage drop.

 

[wyliesdiesels]

I'am sure wylie meant same trench.

I meant that all the communication canling can be in one conduit, which is what he asked. I edited my post!

 

[CNGsaves]

Also on your low voltage conduit of wires (ie CATV, ethernet, phone, etc - - in say 1" PVC sch 40) should be seperated from the electrical by approx 12 inches to avoid any interference. Thus, best setup would be 2" pvc sch 40 conduit at bottom of trench (ie 30" or whatever local code is for city in Ohio) with your 2-2-2-4 aluminum mobile home feeder. Then at higher level in trench, you'd run your 1" conduit for low voltage (say 15" to 18" deep).

Also see prior threads where sparky's like PattenB cover that the 2" pvc conduit needs to be Sch 80 once it comes above ground for your electrical.

 

[Fishplate]

You will need two 1/2" ground rods spaced 6' apart with one continous bare cu wire clamped to each rod and terminated in the subpanel.

Unless I misunderstand you, you can't have two grounds on one system - in this case, one at the main panel and one at the subpanel. (I'm not talking about two ground rods on one wire).

When you have two earth grounds, you risk having an electrical potential between them - which is what we here in the mountains call A Bad Thing...

 

[pattenp]

Yeah after reading again I caught that the OP was asking about running all the low voltage together. I was thinking he was asking about running the LV with the HV in the same conduit. My flub.

I meant that all the communication canling can be in one conduit, which is what he asked. I edited my post!

 

[wyliesdiesels]

Unless I misunderstand you, you can't have two grounds on one system - in this case, one at the main panel and one at the subpanel. (I'm not talking about two ground rods on one wire).

When you have two earth grounds, you risk having an electrical potential between them - which is what we here in the mountains call A Bad Thing...

Ugg! Where do people come up with this stuff! I think grounding has got to be the most confusing thing for people to grasp as evidenced above!

No, incorrect. Where did u hear(or read) this? How would u have an electrical potential between 2 ground rods when theyre at the same potential(earth)? Current doesnt normally flow over ground rods because ground rods are for grounding out lightning.

Ground rods are required at every detached building with an electrical system whether the electrical is fed from another building or its own service!

 

[CNGsaves]

^ ^ Only logical that you want SHORTEST PATH for lightning to get to ground !! Thus, totally makes sense to have ground rods required for detached garage.

I sure would NOT want the lightning path to travel back down the buried conduit I just spent big bucks putting in the ground!!

Thanks Wyliesdiesels and other sparky's keeping things safe.

 

[Fishplate]

No, incorrect. Where did u hear(or read) this? How would u have an electrical potential between 2 ground rods when theyre at the same potential(earth)? Current doesnt normally flow over ground rods because ground rods are for grounding out lightning.

It's been 25 years since my NEC class, so I'm a little fuzzy. Turns out separate grond rods may be required if the subpanel is in a different building. If it's in the same building, then no rod.

But:

There must be a grounding conductor between the main panel and subpanel to keep the ground rods at the same potential. Simply counting on the resistance of the earth to be minimal is what causes problems.

For the record, I studied the code from an agricultural perspective, and there are special grounding requirements for some animal facilities, which is where the confusion comes from.

Ground rods are for providing a safe path to earth for all stray currents, not just lightning.

And finally, I don't mind just having my errors pointed out to me. But you can keep the the rest of that nonsense.

LOL.

 

[theoldwizard1]

Ugg! Where do people come up with this stuff! I think grounding has got to be the most confusing thing for people to grasp as evidenced above!

No, incorrect. Where did u hear(or read) this? How would u have an electrical potential between 2 ground rods when theyre at the same potential(earth)? Current doesnt normally flow over ground rods because ground rods are for grounding out lightning.

Ground rods are required at every detached building with an electrical system whether the electrical is fed from another building or its own service!

A picture is worth ...


View media item 33304

 

[Aceman]

Ugg! Where do people come up with this stuff! I think grounding has got to be the most confusing thing for people to grasp as evidenced above!

I agree. It also doesn't help when you spread misinformation in the exact same post:

Ground rods are required at every detached building with an electrical system whether the electrical is fed from another building or its own service!

What you should have said is a grounding electrode system is required at detached structures, ground rods are just one type. It could also be a ufer, water pipe, ground plate, etc.

 

[Marshallcc]

So, let me be sure I have this.

I want 2-2-2-4 wire running thru 2" minimum schedule 40 PVC from a 90 amp breaker in my main box to a 100 amp box in the garage. I want to bury this 2 ft. to be safe. Where it comes out of the ground, the PVC needs to be schedule 80. I want 2 ground rods 8 ft long and 6 ft apart connected by a #6 bare copper wire for the sub panel since it is in a remote location and not in the house. I can run all my low voltage stuff together in a separate conduit from the main wire and I should bury it a foot away or a foot above for interference reasons. The welder shouldn't be a problem at this point since I am going to the larger box.

Two more questions.

How much of the ground rods should be above ground?

Wylie, can you elaborate on insulating/isolating the neutral bar from the enclosure and ground bar?

You guys have been a gigantic help. I really appreciate it.

Cheers

Mark

 

[Bib Overalls]

Modern electric panels come with two ground/neutral bars. The ground is directly attached to the panel box. The neutral is isolated (insulated) from the box. The panel will most likely come with a screw that can be used to "bond" the neutral bar to the panel box when required. For your application put the screw in the coffee can where you collect fasteners that are you will, most likely never use but are too good to throw away.

I always drive the rods below ground level and keep them exposed for inspection.

 

[theoldwizard1]

So, let me be sure I have this.

I want 2-2-2-4 wire running thru 2" minimum schedule 40 PVC ...

That is 2-2-2-4 ALUMINUM wire.

If you are using Mobile Home Feeder (MHF) cable it can be direct buried. The transition for below ground to above should be through a "sweep", a large radius bent piece of conduit, from the bottom of the trench to vertical.

If you do direct burial, lay the cable, fill the trench about 6" or so and then place a piece of buried electric cable warning tape the length of the trench. Then finish the fill.

 

[Charles (in GA)]

The wire for the ground rods must be one single, continuous wire. From one rod, to the other, to the panel. Only kinds of splices permitted in them are certain approved permanent ones such as Exothermic welding. The rod connections are generally done with an approved connector with set screw in the side of it to tighten it up.

Charles

 

[pattenp]

Panels come with ground/neutral bar(s) installed with plastic risers that insulate them from the case. There is either a screw through the bar into the case or a strap from the bar to the case that grounds the bar(s) to the case. When using the panel as a sub panel the screw or strap needs to be removed so the bar(s) become isolated/insulated from the case so the bar(s) can be used only for the neutrals. A ground bar kit needs to be purchased and when installed it is directly screwed to the case using existing mounting holes in the case. This makes the ground bar bonded to the case and this is now where all the ground wires will be connected. The only place where the grounds and neutrals are connected on the same bonded bar(s) is in the first panel at the main service disconnect.

.....

Wylie, can you elaborate on insulating/isolating the neutral bar from the enclosure and ground bar?

 

[wyliesdiesels]

I agree. It also doesn't help when you spread misinformation in the exact same post:



What you should have said is a grounding electrode system is required at detached structures, ground rods are just one type. It could also be a ufer, water pipe, ground plate, etc.

I was in a hurry on my way to work and didnt have the time to eleaborate or think about posting the correct term. We were on the subject of ground rods so thats why I said that but YES, I should have said grounding electrode system!!!

 

[sands35]

So, let me be sure I have this.

I want 2-2-2-4 wire running thru 2" minimum schedule 40 PVC from a 90 amp breaker in my main box to a 100 amp box in the garage. I want to bury this 2 ft. to be safe. Where it comes out of the ground, the PVC needs to be schedule 80. I want 2 ground rods 8 ft long and 6 ft apart connected by a #6 bare copper wire for the sub panel since it is in a remote location and not in the house. I can run all my low voltage stuff together in a separate conduit from the main wire and I should bury it a foot away or a foot above for interference reasons. The welder shouldn't be a problem at this point since I am going to the larger box.

Two more questions.

How much of the ground rods should be above ground?

Wylie, can you elaborate on insulating/isolating the neutral bar from the enclosure and ground bar?

You guys have been a gigantic help. I really appreciate it.

Cheers

Mark

Caveats...

Since the sub feed wire is protected by the 90 amp breaker in the main panel, you can use any size panel in the sub that is rated 90 amps or higher. So you can use a 100 or a 200 amp sub panel. Just make sure you keep the ground and neutral isolated in the sub panel. (you may need to buy a ground kit for the panel. Panels *may* come with a bonding screw as well - which should not be installed in a sub). The purpose of the sub panel breaker main is as a disconnect only, not as a current protection device.

I say this because you may want more breaker spots than what you might be able to find in a typical 100 amp sub panel.

If you are starting the garage from scratch, tell your contractor to install a "Ufer" ground. MUCH simpler. On the ground rods, I'm frankly not sure about how proud they need to be of the ground, but the houses I've been at have had them only an inch or even level with the landscaping so probably only inches above grade.

 

[Aceman]

Ground rods must be installed flush with or below grade. If they're sticking out they need to be pounded in further.

 

[jam0o0]

Ground rods must be installed flush with or below grade. If they're sticking out they need to be pounded in further.

Is this an Oregon thing or is that NEC? the ground rods for my last 3 houses were all 4+ inches out of the ground.

 

[pattenp]

It's an NEC thing. A full 8ft length needs to be in contact with the soil and is required to be driven flush or below the surface unless the upper end and connector is protected. 2011 NEC 250.53 (G)

Is this an Oregon thing or is that NEC? the ground rods for my last 3 houses were all 4+ inches out of the ground.

 

[Aceman]

It's an NEC thing. A full 8ft length needs to be in contact with the soil and is required to be driven flush or below the surface unless the upper end and connector is protected. 2011 NEC 250.53 (G)

I take that to mean if you have LONGER than an 8' rod you can leave some sticking out as long as you protect it. But nobody uses longer rods just to leave them sticking out. Most everybody uses 5/8 x 8' galv rods, which means you bury all 8' of it to be code compliant.

 

[pattenp]

That's what it means. I'm just citing the code, I didn't write it. I don't know what the purpose would be to have a rod longer than 8' and leave a few inches out of the ground just to turn around and have to protect it. I agree with you.

I take that to mean if you have LONGER than an 8' rod you can leave some sticking out as long as you protect it. But nobody uses longer rods just to leave them sticking out. Most everybody uses 5/8 x 8' galv rods, which means you bury all 8' of it to be code compliant.