• I am moving my main electrical panel 200A to a utility room at back of the house.
  • Given this new distance, an outside disconnect will be installed, technically rendering the new indoor panel a sub-panel.
  • To reach it, I’ll be running 75’ of 4/0 SER cable so I have the separate grounding leg.
  • I’ll have 2” PVC conduit to sheath the SER where it runs out of the disconnect (MAIN) until it passes through concrete foundation.


  • Can I run the 4/0 SER on a running board installed on the flat, attached to the underside of the joists? Clearance to the vapor barrier below ranges 13” to 18”.


  • Can I attach the SER to the inside of the 2”x8” floor joists (which run in parallel with the SER path)?


  • Should I install a running board on the vertical, parallel-to but below the joists, so that the SER can be seen from above?
  • You said disconnect is there a main breaker prior to entering the home? We used to run from the meter to a central location in conduit for some builds but the service had to be in conduit until a fuse or circuit breaker once it entered the building envelope.
    – Ed Beal
    May 5, 2021 at 13:50
  • 1
    The main breaker will be located on the side of the home, upstream of where this SER cable will be run. Therefore as a feeder, I was sure conduit wasn’t necessary. I’m looking for information on how to correctly run/protect the 4/0 SER through the encapsulated crawl space. Thanks again. May 5, 2021 at 16:42
  • You can't run unfused wires over such a distance through the home, so a main breaker will be required at the meter. Fortunately, due to NEC 2020 requirements, standalone 200A main breakers and "meter-mains" are popular and low cost. Note that this turns the large panel into a subpanel, with the ground rods still back at the meter. May 5, 2021 at 21:30
  • Harper thanks for your reply; there will be a main 200 A breaker on the side of the house prior to the SER entering the building envelope (at the meter). A grounding rod there at the meter too. Is it required by the NEC 2020 to have a second grounding rod at the panel (now a sub panel with unbonded grounding/grounded terminals)? I didn’t think so due to the separate green leg within the SER cable but I want to double-check. Thanks again. May 6, 2021 at 13:17

2 Answers 2


I would simply run it attached to the side of the joist

I would simply attach your run to the side of the joist so that it's set back upwards of 1¼" from the joist edge (to avoid the need for a nailplate). Attaching it to the joist can be done with straps or staples designed for 4/0 SER cable (note that SEU cable staples/straps are not usable for SER cable as the two are shaped differently).


Ok with the overprotection protection prior to entering the home envelope you can run the cable without conduit.

With that size cable a perpendicular run no running board is needed according to the NEC 334.15.c this is exposed work in basements and crawl spaces for NM #6 and larger do not need a running board.

Since you are running parallel: If you run it on the side of the joist it shall be 1-1/4” away from either edge of the joist.

  • Thanks for the replies. Can someone direct me to chapter/verse in the 2020NEC that governs rules for running feeders such as this? Or what’s the max. length between staples/support? Also how does one determine the turning radius of 4/0 SER? Jun 30, 2021 at 16:27

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