Sub Panel wiring questions...

[WI/MI Border]

I have some experience with electrical installations, however, please respond as though I have no idea what I'm doing.

I have a new 200a QO main panel upgrade in my home and I want to run 100A to a subpanel in an unattached garage. Yes, I want the full 100a service to the garage, not 90a, not 70a. A new 100a QO DP breaker (for garage feed) is installed in the new main panel. I'm running 50' to the sub panel, in a 24" deep trench, inside conduit. I have no electrical inspection when finished (yes, I'm sure. I've asked the city and the city's building and codes administrator). Regardless, I want to install safely and according to code. And I am not too concerned about cost; I just want it sufficient for a 100a load.

An additional conduit will have ethernet cable. Another 1 1/2" conduit will be installed (empty) for a future solar array (grid tied)

For the 100a feed ONLY...
What gauge and type wire should I use? Aluminum or copper? (Subpanel and main are aluminum lugs.)
I can install grounding rods and wire at the garage, or use the main panels ground. What should I use?
What size conduit is suggested for the suggested feed wires?

 

[mm08822]

Use 2 #1 xhhw, 1 #2 xhhw and 1 #6 xhhw green. These can fit in 1-1/4" pvc. Go to 1-1/2" if PIA conduit route.
All Aluminum
Will need 2 grd rods at garage. 1/2 x 8' rods.

 

[Chuckster in NJ]

 

[PCustoms]

Use 2 #1 xhhw, 1 #2 xhhw and 1 #6 xhhw green. These can fit in 1-1/4" pvc. Go to 1-1/2" if PIA conduit route.

Copper?

 

[mike93lx]

Copper?

Aluminum based on that sizing

 

[mike93lx]

Fully install your conduit, then **** a string through, pull it out, measure then order wire.

Wireandcableyourway.com has great pricing and you can get exactly the length needed

 

[PCustoms]

Aluminum based on that sizing

Either I've screwed up twice or it's aluminum...

240v, 100A, 50'

What am I missing

 

[mike93lx]

Either I've screwed up twice or it's aluminum...

240v, 100A, 50'

What am I missing

#1 Al is good for 100a. The typical #2 is only good to 90a.

What are you concerned about?

 

[PCustoms]

#1 Al is good for 100a. The typical #2 is only good to 90a.

What are you concerned about?

No concerns, just punched it in to a few calcs and it didn't compute. I'm assuming there's some upsize breaker rule or temp that I didn't consider

 

[mike93lx]

No concerns, just punched it in to a few calcs and it didn't compute. I'm assuming there's some upside breaker rule that I didn't consider

The 50' is short enough to not matter

 

[Cruzan80]

Agreed with the above. #1 Aluminum is good for 100A (what I ran for my detached garage). Pull 4x total wires (poster above has a smaller neutral and ground listed) and the garage gets grounding rods as well. In the sub panel, make sure to separate neutral and ground. Depending on the panel, remove bonding screw if present, and you may need to buy a separate strip for ground wires, if you can't isolate L/R strips from each other. You may need to buy an "adapter lug" if the wires from the conduit don't fit on the strips for neutral and ground. Check if your panel requires NoAlOx, or other goop for Aluminum attachments. For the sub panel, the main breaker can be bigger than 100A if needed, the breaker in the main provides the protection.

Mostly, this is repeating what people on here told me 6-7yrs ago when I asked the same before running mine. Be glad it hasn't turned into a "We know you said 100A, but we know better than you, so you should really just run 90A with MHF, for your own good...".

 

[mike93lx]

Check if your panel requires NoAlOx, or other goop for Aluminum attachments.

I think that's really dictated by the wire manufacturer, and in most (all?) modern cases, it's not required but people still often use it

 

[WI/MI Border]

Thanks guys. Exactly the info I'm looking for. I will probably be doing this diy, but, if I can find a reasonable contractor I might have it done instead. I appreciate the information.

 

[Cruzan80]

Thanks for the clarification. I knew it was listed as Required/Not, but for some reason, I thought it was the termination brand that made the call. Makes sense it is the wire manufacturer, as the wire is what could be oxidizing.

 

[sparky 1971]

No concerns, just punched it in to a few calcs and it didn't compute. I'm assuming there's some upsize breaker rule or temp that I didn't consider

You must have used the Southwire website calculator and it came back to tell you that 100 amps isn't allowed on a #1. Try it on the app and it comes back #1 allowed with a 1.03% drop.

 

[mm08822]

Copper?

Aluminum.......copper too much $$$$$

 

[mm08822]

You must have used the Southwire website calculator and it came back to tell you that 100 amps isn't allowed on a #1. Try it on the app and it comes back #1 with a 1.03% drop.

I use the mobile app from SW. They fixed their problems several years back. I even emailed them showing them a few errors I found before the fix

The problem for some today is not using the proper settings in the app. Check the "System Parameters" and the gear icon in the app. and Just jumping into the "circuit Parameters".....= User input error = garbage in = garbage out. The app defaults to 60C ampacities unless you change it to 75C.

 

[sparky 1971]

I use the mobile app from SW. They fixed their problems several years back. I even emailed them showing them a few errors I found before the fix

The problem for some today is not using the proper settings in the app. Check the "System Parameters" and the gear icon in the app. and Just jumping into the "circuit Parameters".....= User input error = garbage in = garbage out. The app defaults to 60C ampacities unless you change it to 75C.

They haven't fixed it on the regular version. Use the SW calculator that comes up from Google and it will tell you that #1 AL can't be used for 100 amps after entering the parameters to find actual voltage drop. It didn't give me an option to change anything that I saw. I use the real app all the time, but the device with the app is in my truck, it's raining, and I'm lazy.

EDIT. I found it. It has to be changed from the default residential to commercial 75°. Different from the app.

 

[mm08822]

They haven't fixed it on the regular version. Use the SW calculator that comes up from Google and it will tell you that #1 AL can't be used for 100 amps after entering the parameters to find actual voltage drop. It didn't give me an option to change anything that I saw. I use the real app all the time, but the device with the app is in my truck, it's raining, and I'm lazy.

EDIT. I found it. It has to be changed from the default residential to commercial 75°. Different from the app.

Are you using the Commercial parameter at 75C? (I'm on the android app only)

 

[sparky 1971]

Are you using the Commercial parameter at 75C? (I'm on the android app only)

I wasn't. I edited my post, but it was after you read my original post and before you posted your quote.

 

[NostraThpmas]

I know OP said he wasn't getting it inspected but for future readers of this thread, don't make my mistake. 250.52 says that a ground rod is required to be at least 5/8" of an inch unless the rod is listed, then a 1/2" rod is permitted.

Also see Electrical FAQs

 

[WI/MI Border]

Are copper clad ground rods code compliant?

 

[WI/MI Border]

Fully install your conduit, then **** a string through, pull it out, measure then order wire.
...

Good point. I was going to just estimate length and add about 10%. This is a better method.

 

[mike93lx]

Are copper clad ground rods code compliant?

Yes. They are all steel core with copper plating

If your soil is rocky, use the trench as a 24" head start for the ground rods.

 

[WI/MI Border]

...Be glad it hasn't turned into a "We know you said 100A, but we know better than you, so you should really just run 90A with MHF, for your own good...".

Yep, I've learned to head off some of those types of replies. Up front details certainly reduce those posts but doesn't eliminate them.

Forums will be forums after all, but I've had a good experience here and usually get the answers I'm looking for. Sometimes replies are confirming what I was thinking.

 

[WI/MI Border]

Yes. They are all steel core with copper plating

If your soil is rocky, use the trench as a 24" head start for the ground rods.

Thanks. In my days as an Ace Hardware electrical department buyer many decades ago I remember, maybe wrongly, that the ground rods were copper alloy throughout.

I always wondered why we can't use copper pipe as an in ground ground. Maybe because it won't stand up to the driving part.

 

[mm08822]

Thanks. In my days as an Ace Hardware electrical department buyer many decades ago I remember, maybe wrongly, that the ground rods were copper alloy throughout.

Could have been, but every years stuff gets cheaper to maintain profit margins.

If they are listed components then there is little to worry about as long as you install/use item as directed by mfr.

 

[mike93lx]

Thanks. In my days as an Ace Hardware electrical department buyer many decades ago I remember, maybe wrongly, that the ground rods were copper alloy throughout.

I always wondered why we can't use copper pipe as an in ground ground. Maybe because it won't stand up to the driving part.

A ground rod is 2/3 the cost of a piece of 1/2" pipe

 

[Chuckster in NJ]

When I was working in Saudi Arabia they used 100% solid copper ground rods but I have never seen them used in the USA.…….. I have driven many 3/4”x 10’ ground rods and they were also copper coated.
Copper is very soft and would easily mushroom over compared to a steel rod that mushrooms over in some tough soil conditions like shale or rocky conditions.

TIP! "IF" you encounter hard driving conditions I suggest putting the acorn clamp over the rod before the rod head mushrooms over and the clamp can’t be installed.

 

[mike93lx]

A 5/8" rod fits right inside the chuck of a sdsmax demo hammer. So much nicer than a sledgehammer and you can get cheap ones online now, or rent one

 

[sparky 1971]

A 5/8" rod fits right inside the chuck of a sdsmax demo hammer. So much nicer than a sledgehammer and you can get cheap ones online now, or rent one

They also fit inside a spline drive, I have one and it's only purpose in life is for driving ground rods; I put a zip tie around the trigger and walk away to do something else but the tip of the drill hits the ground and stops driving with about 4" of rod sticking out of the ground, driving them in the trench prevents that but sometimes there isn't a ditch so the sledge hammer has to come out as a finisher. I did buy the driver attachment for my SDS Max, but it doesn't work near as well as the spline drive.

 

[sparky 1971]

It's been over 25 years ago, but when I was in TX we had some type of soft metal galvanized ground rods, all I remember is that they were silver but I don't think they were AL. I'm sure they were cheap because they weren't worth a damn. It never happened to me but the shop had a couple of chipping hammers we could check out, some of the guys had the heads of the rod mushroom out so bad that it would be stuck in the hammer and have to be sent in for replacement.

 

[WI/MI Border]

A 5/8" rod fits right inside the chuck of a sdsmax demo hammer. So much nicer than a sledgehammer and you can get cheap ones online now, or rent one

Good to know. I have an SDS+ and it is a beast at drilling. I'll have to check to see if the chuck fits.

 

[sparky 1971]

Good to know. I have an SDS+ and it is a beast at drilling. I'll have to check to see if the chuck fits.

It won't fit in an SDS+ but there are ground rod driver bits for them...

Amazon.com : sds ground rod driver

I have my doubts about an SDS+ being up to the task but will also admit to never trying it out. For $10 it's definitely worth a shot though.

 

[manwithtools]

Good to know. I have an SDS+ and it is a beast at drilling. I'll have to check to see if the chuck fits.

It won't fit in a SDS+, but for $9.99 you can get an adapter made for the job: SDS Plus Ground Rod Driver

 

[WI/MI Border]

Can someone educate me on a couple things with this graphic?

• In the main panel it "appears" that the feed wires to the subpanel are connected to a single pole (blk wire) and a double pole (red wire)? That really confuses me. Is this just a poor graphic or am I really missing something?

• In the main panel the ground and neutral are connected. Is that what is referred to as "bonded N and Grd"?

• It was suggested here that the subpanel not have Grd and N bonded. Is it as simple as removing the jumper? Can you explain why it should be removed?

There will be more ? : ) Thanks for the help...

 

[PCustoms]

It won't fit in a SDS+, but for $999 you can get an adapter made for the job: SDS Plus Ground Rod Driver

I think you missed a period there...

 

[WI/MI Border]

It won't fit in a SDS+, but for $999 you can get an adapter made for the job: SDS Plus Ground Rod Driver

I can beat my brains out with a sledge before I buy that $999 adapter... hahaha

 

[manwithtools]

Yep, my bad.... it's $9.99. Corrected the post.

 

[sparky 1971]

Can someone educate me on a couple things with this graphic?

• In the main panel it "appears" that the feed wires to the subpanel are connected to a single pole (blk wire) and a double pole (red wire)? That really confuses me. Is this just a poor graphic or am I really missing something?

It's just a bad picture, they should both be on a two pole breaker.

• In the main panel the ground and neutral are connected. Is that what is referred to as "bonded N and Grd"?

Because the neutral is mechanically bonded to the ground.

• It was suggested here that the subpanel not have Grd and N bonded. Is it as simple as removing the jumper? Can you explain why it should be removed?

Yes, the main breaker panel will come with a green screw that may or may not be installed. Take it out and throw it away. You will also have to buy ground bars, more often than not, the panels don't come with them. Get two, one for each side to make things easier.

There will be more ? : ) Thanks for the help...