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Situation:

  • 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.

QUESTION:

  • 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”.

Or

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

Or

  • Should I install a running board on the vertical, parallel-to but below the joists, so that the SER can be seen from above?
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  • 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 '21 at 13:50
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    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 '21 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 '21 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 '21 at 13:17
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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).

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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.

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  • 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 '21 at 16:27

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