I'm installing a subpanel in a shed and my buddy has 150 ft of leftover TC-ER Cu Awg 4-3 THHN w/ #8 GND, which he got here: https://www.wireandcableyourway.com/4-3c-thhn-pvc-tray-cable-with-ground

Is there any issue running that from my main panel, thru the attached garage, into my attic, out thru the exterior wall, down the wall into the ground, along the ground, and up into the shed?

I am hoping to run the interior sections without conduit (though I could) and the only conduit during the exterior wall (maybe studs?) and underground sections.

The other points are: 125-150ft from main to sub, 70 amp breaker, 2 grounding rods 6 ft apart, No neutral bonding

Aerial View

  • 1
    It needs to meet THWN or other waterproof spec for burial. most THHN does.
    – Jasen
    Mar 10, 2021 at 11:15
  • Can you post photos of the label on the inside of your main panel's door please? Mar 10, 2021 at 12:44
  • Very strongly recommend using conduit in the ground for future proofing. If you ever need to replace, add, upgrade cable, that saves you having to dig a new ditch. It also means that this ditch can be shallower. I'd also suggest the straightest run possible once you're outside the house, but the current pink line may just be for "show" not the actual "plan". (Or there may be a large rock, swimming pool, etc in the way...)
    – FreeMan
    Mar 10, 2021 at 13:28
  • Tray cable is regularly used for mini splits it is rated for outdoor use but I don’t remember underground. I will check it when I get back to the office. It will require conduit inside.
    – Ed Beal
    Mar 10, 2021 at 16:19

1 Answer 1


Type TC cable is for tray cables it requires a cable tray or raceway.

Smurf tube would be the perfect option inside the home as it is cheap and flexible. Non metallic flex conduit is commonly called smurf tube because it is often blue, but could be other colors orange is usually reserved for fiber but that doesn't stop a user for using it in there home for this.

The cable is wet rated and can be direct buried if rated for direct burial if not it will require conduit for the conditions.

The information can be found in article 336 of the NEC it’s only ~2 pages long so not hard to read up on this type of wire.

When sizing the conduit a single wire or cable is limited to a 53% max fill I did not see tc listed for area so you may need to measure yours and make sure the conduit you use inside the home is large enough. For the cable you are using.

  • 53% of max fill means you take the widest width of the cable, multiply by 1.38, and the conduit must have an inside diameter at least that large. Mar 10, 2021 at 23:37
  • This wire is TC-ER, so my understanding is that it can be "exposed run", which I thought meant no need for conduit. My goal if acceptable was to run exposed through the attic and into conduit during the outdoor/underground sections.
    – Merkd
    Mar 11, 2021 at 18:22
  • Merkd, as my answer states conduit is required by code. Specifically NEC 336.12.2 uses not permitted. Installed outside a wire way or cable tray system there are exceptions 336.10.4 when supported by messenger wire. 336.10.7 but all the following are needed “conditions of maintenance and supervision (industrial locations) . 336.9 my state allows for generator &hvac since 2014 code inside still required conduit . In the 2020 code it requires tc-ep-JP to be used similarly to nmb so I would check with your AHJ since black it will look like large nmb if that helps but needs conduit by code.
    – Ed Beal
    Mar 11, 2021 at 20:01
  • Ed Beal, thank you for your education. Would you recommend any alternatives? Maybe a 4/3 NMB run through the interior attic to an outdoor junction box that is transitioned to THHN conductors and conduit for the exterior wall and underground sections? (trying to avoid a lot of conduit if it's acceptable by code... Thanks again
    – Merkd
    Mar 12, 2021 at 19:01
  • The TC is fine it just requires a conduit it looks like 100’ inside or less. Depending on the diameter of the cable 1-1/2 was about 1.5$ per foot so if your friend is giving you a good price this would be the way to go. They do make 4-3w ground nmb but it’s spendy and would be a bear to pull. At that size most electricians will go to individual (aluminum feeder) wires and conduit so you still have the conduit cost. For a residential feeder I will use aluminum because the loads don’t go from 0-80% constantly so it lasts in that application.
    – Ed Beal
    Mar 12, 2021 at 19:33

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