detached shop sub-panel

[40cpe]

Hi everyone, this is my first post on this forum. I'm on the Fordbarn every day and on the HAMB occasionally. I've been into cars, and therefore shops, all my life. I'm 69 and am in the process of having built a 30'x40' metal building to catch the overflow from my existing 1100 sf shop. I anticipate not having time left to fill this one up, thought I hope I'm wrong.

I'll be doing the wiring. The panel in my existing shop is fed via an overhead #4 triplex and a 50 amp breaker from the meter base/breaker box (called a housepower box back in the day). This shop is about 12' from the existing shop, so I'll be running about 25' total run from the existing triplex fed panel underground through PVC to a 12 circuit panel in the new shop. Although I'm making allowances for lights and a welder now, I want capacity for other luxuries if needed.

My questions are: I plan on using #2 aluminum. Do I need 4 wires or three, since I only have three feeding my existing panel? Should I use an underground rated bundled cable or individual wires? And finally, what size conduit is appropriate? This project won't be inspected, but I do want it safe.

a 50 amp breaker might not seem sufficient for the area of the two buildings, but my existing shop has been fed like this for 25 years with absolutely no problems. I'm the only one working (?) in there, so it isn't likely that there will be multiple tools running at the same time.

Any advice is appreciated.

 

[pattenp]

You should go ahead and run four wires. The wire can be either a 4 conductor direct bury cable such as Mobile Home Feeder or 4 individual THHN/THWN wires. The wire needs to be suitable for wet locations when in conduit underground. You will need ground rods at the new shop plus do not bond the neutral to the ground in the new panel.

For #2 Al I'd use 2" conduit.

 

[40cpe]

10-4 and thanks for the grounds and bonding advice. If I used individual wires would 2-2-4 with a #6 cu suffice? I would like to do with a little smaller conduit than 2" .

 

[pattenp]

2-2-4-6 in copper is way more than you need. #2 Cu is good to 115A @ 75C. If you are looking at 50A to the new sub-panel then #8 Cu is all you need with a #10 ground. If the #4 Triplex to the first panel is CU then you can push the over current protection on that panel to 90A. If the #4 Triplex is Al then you can push it to 70A. The actual #4 amp rating @ 75C is 85A CU and 65A Al, but code allows you to use the next higher standard sized breaker.

 

[40cpe]

I apologize for not being clear. I intended to use 2-2-4 AL to a 12 circuit main lug panel and was asking if #6 cu is kosher for the ground, and if by using individual wires could I use a smaller conduit than the 2" you recommend? I'm in a 3 1/2" wall and 2 inch conduit is stiff and bulky.

I appreciate your willingness to share your knowledge with us.

 

[pattenp]

You can use #8 Cu or #6 Al for the equipment ground on a circuit protected up to 100A. So the #6 Cu is okay. What rating does the 2-2-4 Al have? If it's a URD with just a USE-2 rating then it shouldn't be used inside.

I wouldn't go any smaller than 1 1/4" conduit.

Edit: You will need a main disconnect at the shop if you have more than a 6 breaker panel, so it's best to use a main breaker panel, not a main lug.

Why are you using 2-2-4 if you are only doing 50A?

 

[40cpe]

I'm upsizing the wire because the run is so short/inexpensive that I would rather do it now and be safe for larger loads in the future. I realize that since it is so short I could easily replace it in the future, but I had to choose.

I plan to use the proper wire suited for conduit/wet locations. I was going to let the supply house recommend.

Thanks for the advice on the panel. I'll use the main breaker.

 

[pattenp]

If you are running the new wire from panel to panel make sure you let the supply house know. They may try to sell you USE/USE-2 only rated wire which is a wet location and direct bury but can not be used inside.

 

[40cpe]

Will do. thanks for all your advice

 

[royalton10]

Don't be afraid to put in a bigger panel than the 12 circuits you mention above. If you have several 220 circuits, some lights and outlets, you will be 6 plus before you even get started.

Enjoy the new building!