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I've checked a number of the other questions but not finding the specific answer I need.

I'm wiring a 100 AMP garage sub-panel from a 200 AMP main in my house. I plan to install a 100 AMP circuit breaker in the house panel. The run to the garage, lug to lug is ~65' and I have to bury the cable to meet code and am going to put it in Sched 40 conduit.

I'm thinking I can use 1/0-1/0-1/0-4 AL but since it needs to go underground am confused about SER vs MHF and hoping I can find a solution that doesn't require changing cable to go from underground outside to inside the house and garage. The NEC chart isn't particularly helpful to me.

Also, what is my option for copper instead?

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  • Is it in conduit the entire way or only for the underground bits?
    – Harper - Reinstate Monica
    Jul 24, 2017 at 16:15
  • I'm planning on running conduit the entire way from box to box.
    – ruckhus
    Jul 24, 2017 at 17:33
  • Use Sch 80 for any above-ground exterior bits as "exposed to damage" - honestly, consider Sch 80 the whole way, it's not so much more expensive, though you may need to go to an electrical supplier, not HD/Lowes to find it.
    – Ecnerwal
    Jul 24, 2017 at 17:59

2 Answers 2

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Your options are a minimum of #1 aluminum or #3 copper.

Since it's only 65 feet I wouldn't upsize it for voltage drop.

You don't need service entrance or direct burial type cable if you are running conduit underground you can use type THWN wire. Individual wires not cable. If you don't want to run conduit you can buy direct burial type wire like You are talking about.

Good luck and stay safe!

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  • Thanks, would it be easier to pull 4 single wires taped together at the pull end, or a cable? Either way, it's going in conduit.
    – ruckhus
    Jul 24, 2017 at 17:35
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    Individual wires pull MUCH easier. You pull them all at the same time...one after the other is more difficult and sometimes impossible to the point of pulling all the wire out and adding the new wire before pulling it back in (not always, but sometimes.)
    – Ecnerwal
    Jul 24, 2017 at 17:54
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    If you're pulling wires or cable, don't forget to pull an extra string in, just in case you ever need to pull an extra wire in for some reason.
    – Spark
    Jul 24, 2017 at 18:51
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Since the entire route is conduit, you want to run this in single-conductor THWN wire. Generally multiconductor cable is less desirable in conduit because it is difficult to wield.

When laying out conduit, make sure to put pulling points in as many corners as possible. Otherwise the pull can be rather difficult with heavy conductors.

In any case, you must still use outdoor rated cable, so SER is out of the question. And you must run 4 conductors. (Unless you really want 120-only or 240-only, but you don't.)

Use aluminum. Yes, really. You may have heard the bad press about copper and aluminum wiring interacting badly and starting house fires. That is due to dissimilar metals corrosion and thermal (expansion) issues; copper lugs do not like aluminum. (The reverse is untrue). Large wires are expected to be aluminum because copper is rather expensive. As such, the lugs are aluminum. The trouble with Copper is it will have corrosion/thermal issues with the lugs. Isn't that what we're trying to avoid?

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  • I always prefer to over rather than under build so there is room for growth if needed. What I'm getting from the two threads is 4- minimum #1 aluminum THWN wires pulled at the same time, through Schedule 80 conduit. Although for the conduit it's interesting Dominion Power mandated Schedule 40 both in and above ground for a new main power line from pole to my house.
    – ruckhus
    Jul 24, 2017 at 19:23
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    best way to overbuild is use extra large conduit. It will make pulling easier. You might also consider using Rigid conduit, which is the cadillac of conduit and will let you bury to 6" instead of 18". Rigid can also serve as a ground path, and removes the necessity of running a ground wire. However it is actual pipe and requires genuine pipefitting, so you will be threading metal pipe a lot.
    – Harper - Reinstate Monica
    Jul 24, 2017 at 20:38
  • Pulling points at all corners isn't really necessary, but keep track of the degrees of turn since the last pulling point. >180 and pulling starts to get challenging. It becomes pretty much impossible at 360. And you can get anti-oxidation grease for the terminals. Makes a big difference even if they're the same type of metal. Use it on the battery posts of your car too.
    – Perkins
    Sep 15, 2017 at 22:37
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    @Joe You are talking about multi-strand: which is seven (usually) individual wires gently twisted together and covered with an insulator. Each such combination can be used for neutral, a phase wire. Harper is talking about multi-conductor where each conductor (either solid wire or multi-strand) is tied together in an outer insulator and a single "thing" can carry neutral, two phases, and an earth wire.
    – Martin Bonner supports Monica
    Oct 4, 2019 at 13:38
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    @Joe I was unclear on that; fixed. I also possess no solid core wire.
    – Harper - Reinstate Monica
    Oct 4, 2019 at 15:48

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