i am finishing up my basement and about to close up the walls.Before i close the walls, i want to run 100 amp wire from the circuit panel, located on one side of the house, to the other side of the house where my boiler is located (Aprox. 300ft of wire). The wire will not be connected to ANYTHING. I just want the wire to be there for a future detach garage.

My question is how many wires do i need to run? Do i need to run a ground wire too? or, Just one 100 amp cooper/aluminum wire.

Does the wire configuration change for 110 vs 220?

Also, do i need to protect it with some type of piping/conduit?

I am in Ny if that makes a difference.

Again, it is just running the wire from point A -> B so the future electrician doesn't have to break walls.

  • Just a comment, as I don't know size (AWG) you will need - one of the pros will fill in all the details. But the short answer is: 4 wires - 2 hot, 1 neutral, 1 ground; hots & neutral all the same size, ground could be smaller - but how much smaller I can't say for sure; and probably aluminum will save a good bit over copper because this is BIG wire. Mar 20, 2019 at 22:56
  • I take it you finished out with 2x4s? This matters in determining how fat of a wire or conduit you want to leave. Mar 20, 2019 at 23:39
  • Will the destination area be unimproved space, or will you be finishing it out with drywall and all that? Is it feasible to run 2" pipe between the two locations? Mar 20, 2019 at 23:56
  • It is 2x 4 but bc of the layout I can run some pipe. If i don't need to i prefer not to.
    – Padawan
    Mar 21, 2019 at 0:23
  • The point at the panel is finished. The point of the boiler is unfinished.
    – Padawan
    Mar 21, 2019 at 0:24

3 Answers 3


Run a 1.5" RMC

The 60%-of-width limit on bored holes in non-load-bearing studs from IRC R602.6 limits the maximum size of conduit that can be run within a 2x4 partition or furring-wall to 1.5" trade size (2" trade size conduit has a minimum OD of about 2.2", which exceeds the 2.1" limit that 60% of the 3.5" actual stud width/depth sets).

The best choice here then, balancing availability with usable fill, is a 1.5" RMC. This gives you just enough space, at 533mm2 available vs. 528.9mm2 consumed, for a feeder consisting of 3 4/0 Al XHHW-2 wires, with the RMC as the ground. This would allow you to bring 175A maximum, or 100A with voltage drop held below 3%, to the garage, which is adequate for whatever you, or just about anyone else, would want there.

Considering this is merely a provision, though, I would simply run the conduit for now, leaving it unpopulated with wires until the garage is built.

  • "For future use" the only correct answer is conduit. Until the use is determined, the cable requirements are unknown.
    – FreeMan
    Mar 11, 2021 at 16:39

You will need 4 wires, with a 300' run at 100 amps it will take 2/0 copper or 4/0 aluminum to keep the voltage drop below 3% . depending on how you want to install the wire conduit or cable pulled through framing will dictate the actual wire type.

  • But isn't one of those 4 wires ground that can be downsized a bit? Mar 21, 2019 at 14:29
  • 1
    Yes the ground can be downsized but we don't know if cable or individual wires will be used the cable will have it already sized.
    – Ed Beal
    Mar 21, 2019 at 15:26

You'll only need 1/0-1/0-1/0-2 aluminum wire for 100 amps @ 300'.

Allowable Ampacity for 1/0-1/0-1/0-2 Notre Dame Quadruplex Aluminum Conductor 600V URD direct burial: 200 Amps

Allowable Ampacity for 1/0-1/0-1/0-2 Notre Dame Quadruplex Aluminum Conductor 600V URD in duct: 150 Amps

1/0 will fit into breaker lug and sub-panel lugs

Use direct burial wire at 24" deep

Only conduit needed is from wall into ground and ground into wall

4/0 aluminum wire is used for 200 amp service and will not fit into 1.5" conduit

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