Conduit to the Garage

  • Tue 24 January 2017
  • misc

A few weeks ago one of the crew (we'll call him Joe for the purposes of this discussion... because that's actually his name) dropped me email looking for a bit of electric car related advice.

Joe said: "So we are likely to finish the basement in our house next year. Anticipating that within our tenure in this house we may want an electric vehicle, I'd like to run conduit from the panel before we have a ceiling. Since you've done this and know about this stuff generally, any thought on how big a conduit would make sense?"

My advice back to him was a bit of overkill, but it's inexpensive overkill and Joe is the kind of person who needs no convincing in order to be willing to spend a few tens of extra dollars (literally) on future-proofing the installation.

Here's what I wrote:

TL;DR - Run 2" EMT, ENT, or PVC conduit. This is sufficient to support an eyebrow-raising-but-still-eminently-conceivable service to the garage. Labor costs are going to be +/- the same no matter what you put in; the only difference is that 2" EMT is $1.60/foot while 1" EMT is $0.68/foot and 1.25" is $1.05/foot. Hangers and fittings are similarly more expensive for the big stuff. In short, material costs pale in comparison to the labor. A 2" conduit is enough to support a 200 amp subpanel in the garage, or anything smaller you might want to put in down to a single charger. Nobody ever got in trouble with the inspector for not having enough wires in the conduit.

Knowing what I know about your proclivities, I would do the subpanel anyway. If you want a second charger, a welder outlet, or an air compressor you'll be glad you had a subpanel.

Make sure the run is straight or has accessible pull boxes where it turns corners; NEC 346-11 requires no more than four quarter bends (360 degrees of bend) between pull points, but for pulling stuff that's thick enough for a 100 amp panel (3 AWG Cu, 1 AWG Al) or 200 amp panel (2/0 Cu, 4/0 Al) your electrician will thank you for only straight (or keeping it to 180 instead of 3).

One more thing: if you think there's even the tiniest chance of needing Ethernet, fiber, phone, other low voltage stuff out there, put in a parallel run of 1/2 or 3/4 emt, pvc, or even smurf tube. Low voltage conduit requirements are very lax (hence the smurf tube recommendation as it's stupid cheap) but you gotta use a different conduit - it can't share with the power feeder.