Is direct burial MC cable suitable for a detached shop service?

Question

I want to install a 100 amp 230 volt single phase service from my house breaker panel to an external shop building. My house service is 200 amp 230 volt.

Is it permitted to use direct burial MC cable such as Service Wire Co. part no. AAP2/3 [see page 68] (3 conductors of 2 AWG and a 6 AWG bare ground) with aluminum or galvanized steel interlocked armor with a black PVC jacket? Temperature rated at 90 degrees C wet or dry. In the following installation.

I want to connect to the house breaker panel at the power entrance and run about 110 feet thru the house attic then down the outside of the rear house wall and go underground about 80 feet to a metal sided shop building and up and over about 20 feet to a breaker panel. Total length of cable about 210-225 feet.

Reason I am thinking of using MC cable is because I am trying to go under several large tree roots and sprinkler pipes and think it will be easier than installing conduit. However, I am open to suggestions. I am in California.

Answer 1

Can you use Direct burial MC cable? YES. Looking at that long of a run you are pushing the voltage drop limit of 3%. Here is a link to a calculator, 3% is the standard limit. 240V At 80 amps the voltage drop was 2.74% on #2 copper. With 100 amps it jumped the wire to #1 and it was 2.48%. So the real answer will be load dependent. If your expected load is going to be ~80 amps it will work with that size wire and a 80 amp breaker. If you really need 100A the wire size will need to be adjusted.

Answer 2

MC is wonderful stuff

Direct bury (PVC jacket + THWN or XHHW-2 conductor) MC cable is wonderful stuff -- you can run it exposed, concealed, wet, dry, underground, even directly in a poured concrete slab! About the only place it can't go is where it's exposed to physical damage -- that job is reserved for thick-walled conduit such as RMC or Schedule 80 PVC.

However, the 2AWG cable you are suggesting is a bit undersized for your application, as Ed Beal points out. Upsizing to 1AWG would allow you to make better use of the full capacity of your circuit provided you aren't running large continuous loads, which does not seem to be the case for an external shop building like yours. (If you were running mostly continuous loads, then 2AWG would be fine due to the 125% sizing rule for continuous loads in the NEC.)