ground for sub panel

[mx842]

I'm trying to save a little on wiring in my shop. What I want to do is add a couple small 6 space sub panels in two spots in my shop. I picked up a 70 amp 6 space sub panel yesterday that has no breakers in it. I picked up a ground bar kit also.

When I prepared my floor for concrete I laid conduit to different points in the shop where equipment would be placed. I ran a 1" conduit to my welding room and was also going to run another run to the side wall next to this room where my big lift/welding table will sit but never did get around to it.

When I started running wires is when I remembered I never made the second run to the side wall so I decided what the heck I'll just run three wires over to the welding room and then stub off from that plug to the other location and on to the next one a little further down the wall just like you do with a regular rec. Then came the problem of trying to connect 3 #6 or even 2 #6 and a #8 together was not as simple as It seemed on paper. Then it hit me.......I'll just go pick up a small sub panel and run these leads out of it and I could also have a couple spaces left for lights and rec. in my welding room and parts room. All is good....right?

It was after I went an picked up this 100amp 6 space box that I remembered the part about only 3 wires in the conduit over to that room. I would have pulled those wires out and added a #8 leg but it was all I could do to get the 3 #6 wires crammed into that conduit so adding another wire probably wouldn't fit. I did end up with a #12 wire in there along with the 3 large wires somehow don't ask me how that happened but it did.

What I was wondering was if that #12 wire would be enough to use as the neutral feed wire for the box that will feed two 8' fixtures, one in each room and the rec circuit which would have 3 rec in each room and probably 4 along the wall that connects these two rooms?

Another option would be and I don't know if this is right or not but I remember reading somewhere about wire runs all having to be in the came conduit/tray,trench, etc but I also remember reading about ground connection to a sub could be picked up off the building ground system, ufer, ground rod if it was within 6' from the box. I have looked but I cannot remember where I saw that article.

The reason I'm asking about this is that my ground system has 4 ground rods all connected back to the main feed panel in the barn and one of those ground rods is right there on the outside wall from the new sub panel. Can I pick up my ground there and use the third wire in the conduit for my neutral?

Also can you install an Isolated ground circuit in a building that is powered from a sub panel like in a detached garage where the neutral and ground are separated?

 

[terraformer]

I have been through installing a sub box. My electrician told me to not ground directly the sub box but to connect it to a ground wire that goes back to the main panel. I took his advice and ran 4 wires to the main box. My ground rod is at my main box.

He recommended that I not bond the neutral to the box and remove the bus bar. I am using one side for the neutral and the other side hooks all the grounds up.

He had me use 6ga carry the ground from my 100a sub box back.

 

[aczlan]

Personally, I would just use some Split Bolts like these or these (appropriately sized) and tape them well.

That is (IMO) the best way to join 3 wires of that size together.

Aaron Z

 

[mx842]

I have been through installing a sub box. My electrician told me to not ground directly the sub box but to connect it to a ground wire that goes back to the main panel. I took his advice and ran 4 wires to the main box. My ground rod is at my main box.

He recommended that I not bond the neutral to the box and remove the bus bar. I am using one side for the neutral and the other side hooks all the grounds up.

He had me use 6ga carry the ground from my 100a sub box back.

Thanks! Yes, I have read ten thousand pages that say you don't have to install new gr rods for a sub panel in a detached building.....other than of -course the gr rods required at the SE of the detached building. I am good with that but my installation is a little different than most as I have this big steel structure running through it and a 20' steel container in there as well. I extended the #6 wire from my two gr rods at the main panel to an extra one next to the steel tower. I planned to pull off that rod and connect it to the tower and on the other end, 30' away connect another wire and it go to another gr rod at the container and tie them together. I had planned to install another sub panel in that area to feed lighting and equipment in the back part of the building. I wanted to install this panel either next to or on the outside of the container and then the #8, 4 wire lead that feeds this panel will loop the ground wire back to the main panel at the front of the shop.



This picture does not show much but it does give and idea of how the layout goes with regard to the tower and the container I want to tie together. I thought I had more pics that showed every thing now that it is under roof but I can't put my hands on them right now. This picture does show just how much extra steel that is inside the building and it seems to me it should be grounded in some sort of way.

 

[mx842]

Personally, I would just use some Split Bolts like these or these (appropriately sized) and tape them well.

That is (IMO) the best way to join 3 wires of that size together.

Aaron Z

Thank you, I have some of those but have changed my plan and am just going to use those three wires for my welder plugs. I'll just run a new 4 wire lead over there to supply my new sub panel for the lights and other stuff on that side of the building. I found some really big wire nuts that I made the connections with and that part is all worked out.