Sub panel wiring through attic, raceway?

[bikesandcars]

My shop is 64' long and I want to put a 100 amp sub panel on the opposite side of my 200 amp main panel / service entrance.

The most direct route is to go up into the attic and run it across and down. I also view this as safer than having it in the walls.

It's for home shop use. I'm planning on using #3/3/3/5 copper SER. Maybe a little "over-kill" but sound OK?

For the attic I saw that NEC requires protection in a 6' radius around my attic entrance.

Since I want to run other cables to that same side is there some kind of residential cable tray system I should use? I'm running perpendicular to the trusses. Can I make a cable tray out of 2x4's nailed to the trusses and just lay my cable in it?

Thanks!

 

[Raisedonadeere]

Can I make a cable tray out of 2x4's nailed to the trusses and just lay my cable in it?

Thanks!

That is exactly what I did but I hesitate to mention this because I never figured out for sure if it met code. What code reading I did seemed to be focused on protection so I made an effort at protection. Inspector glanced into the attic area, still uncovered, and barely took notice of 6 cables stapled on to the 2x4 running the length of garage down center of outer third of truss span. He then inspected panel wiring, outside trench, grounding, checked polarity of a few receptacles for GFI function and put the beloved green sticker inside the panel door.

Mine did not meet the 6' attic entry way rule as best I could make out and I feared he would ding me for that but did not.

Also I wasn't running any SER cable to a subpanel.

 

[EngineerNate]

Is your attic access just a scuttle hole or a ladder? If the latter you need it protected anywhere up there where it lies on the bottom cord of the ceiling trusses/joists. 6' applies if it's just a hatch/scuttle.


I hard piped all the way to my 60A upstairs subpanel with 3/4 EMT. Gives me a warm fuzzy that something capable of that type of current at 220V is inside a steel tube where rodents and stomping feet can't get to it.

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[wyliesdiesels]

Aluminum SER will be far cheaper

 

[pattenp]

SER cable (NEC 338.10(B)(4) is installed as NM-b (See NEC 334.17 & 23) also refer to 320.23 for attics.

Basically if cable is within 7 feet of attic flooring accessed by a permanent stairway/ladder or 6 feet of an access hole the cable needs to be supported along a running board.

 

[bikesandcars]

Is your attic access just a scuttle hole or a ladder?

Scuttle hole.

I have an elevated walkway from one end to the other so I can travel above the R38 insulation.

I would run the line(s) parallel to the walkway, perpendicular to the trusses, fixed to the trusses above the insulation (height TBD).

Wasn't thinking of doing conduit, the cost of installing it plus the THHN conductors doesn't make it worth it over SER.

No mice in the attic yet, traps are set.

 

[bikesandcars]

Aluminum SER will be far cheaper

Yep, #1/1/1/3 being 1.67 a foot and copper 3/3/3/5 copper being 5.38 a foot.

That's also a consideration for sure, not that the material difference is going to break the bank on this project.

Do most folks use aluminum?

 

[bikesandcars]

SER cable (NEC 338.10(B)(4) is installed as NM-b (See NEC 334.17 & 23) also refer to 320.23 for attics.

Basically if cable is within 7 feet of attic flooring accessed by a permanent stairway/ladder or 6 feet of an access hole the cable needs to be supported along a running board.

No permanent stairway ladder.

Within 6 feet I will install a running board for sure.

Outside of that, can I install a wooden running board / cable tray running the length of the trusses and just lay the cable in it? (I could add a few staples, but it's neater than having it sag between the 4' trusses)?

 

[yatg]

Aluminum SER will be far cheaper

And less weight to deal with.

 

[EngineerNate]

Mine is only 3/4 EMT and 6 gauge conductors, so the cost difference wasn't as stark.

I don't see any issues with your plan. Running boards the whole length of the attic is smart.

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[nadogail]

If your wiring is away from casual contact and physically protected IMHO you will be good.

 

[wyliesdiesels]

Yep, #1/1/1/3 being 1.67 a foot and copper 3/3/3/5 copper being 5.38 a foot.

That's also a consideration for sure, not that the material difference is going to break the bank on this project.

Do most folks use aluminum?

Assuming you’ll need about 90’, thats over $300 difference. Thats a good chunk of change.

Yes most use aluminum.

 

[greenlizard]

I created a cable tray for the same purpose as the OP. It passed all inspections 15 years ago. Had occasion to look it over recently and other than dust, no changes. I like that it prevents stepping on or otherwise putting pressure on wires while still allowing access for additions.