Mike Dolt Enterprises
Mike Dolt Enterprises
User: RathFarm, Location: 50111
Asked on: Saturday, May 29, 2021 at 5:44 pm EDT
Answered on: Thursday, June 20, 2024 at 11:11 am EDT
Question: POCO comes in overhead to a unfused main disconnect. Then UG to house and overhead to outbuildings. Putting in a new 125A panel in main barn (it is an outdoor panel, so I have an option to install it outside the building) and want to run new UG lines (direct bury) between new panel and POCO main disconnect. With copper prices so high, we are looking at aluminum. Need help in determining the size, type of cable, as I am confused between code, online statements in forums, and discussions with electricians.My interpretation is that since we are after the POCO main disconnect, then we must follow NEC, so URD (Underground Residential Disconnect) that POCO's use can't be used. And since we want to do direct bury, the cable must be UF or TW cable. The conductors will need to be 1/0 for copper or 3/0. Since this is after the POCO main disconnect but before overload protection (new panel in the barn), then no ground is needed and just a neutral. I haven't sized the neutral but was planning on matching the conductor size off code memory. Am I missing something?If the above interpretation is correct, the next issue is that it doesn't appear UF cable goes that large. So am I stuck with TW cable, but it doesn't appear to be extremely common. Again , am I missing something?By code, the UG cable must be protected when it comes out of the ground. I plan to put it in conduit, but some have indicated that you can't put TW in conduit. If that is the case, what's my options to transition from UG to the panel?Lastly, in the barn, cabling must be protected anywhere it is 8' or less above the ground. Can I run Romex to surface mount switches/outlets and just put the Romex in conduit below 8' and leave the outer sheath in place?Code references would be appreciated. Thanks in advance for your help.
Cable Sizing and Type
Since you are installing a new panel, NEC applies. As you are using aluminum, you need to refer to NEC Table 310.16. For 125A, you would need 1/0 aluminum THHN/THWN-2 or 2/0 aluminum SER cable. No ground is required for the feeder as it is after the POCO main disconnect.
Underground Cable Options
UF cable is not available in sizes larger than #2 AWG. TW cable can be directly buried. You can also use other direct burial cables such as USE, USE-2, or RHH/RHW-2.
Conduit Requirements
TW cable can be installed in conduit if it is UL-approved for direct burial. NEC Table 300.5 lists acceptable types of underground conduit.
Transition from UG to Panel
You can transition from UG cable to conduit using a direct burial adapter or a pull box. If using conduit, be sure to use appropriate fittings and sealants.
Protection for Cabling in Barn
NEC 210.52 requires protection for cables within 8' of the ground. Romex can be used and protected by conduit or other approved means. You do not need to remove the outer sheath from Romex if it is installed in conduit.
Code References: NEC 338: Underground Installations NEC 310: Conductors for General Wiring NEC 210.52: Protection of Cables and Raceways NEC 300.5: Underground Raceways Flag for review