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Adding a 60amp sub panel (4breakers) on the 2nd floor for a dehumidification system and some misc. Running 100 feet of 6/3 wire. I am assuming that I can use the ground wire in the 6/3 from that sub panel ground bar to the main panel ground bar. This is not in a separate building so I don’t think NEC requires grounding rods. And if so does anyone know the limitation on the length of a ground wire if indeed a separate one is required for the panel itself. Washington country Maryland.

  • Is your 6/3 NM or SE? (It does matter a bit in terms of margin for growth -- SE can use the 75degC ampacity, while NM cannot) – ThreePhaseEel Apr 30 at 22:16
  • It’s nm but there won’t be any significant loads near 60A. Usually just a 38A startup and then 31mca down to 30a or lower in reality. The panel was just for some items I may not think of right now. I needed a 40 amp circuit 100 feet away. So I needed to run 6 and figured having a few empt slots can’t hurt so I’m gonna run 6/3 not 6/2 and have a little panel. :-). Just was concerned about the code for the ground on the sub panel. – James Apr 30 at 23:02
  • In the same building or attached building no ground rod is required just hot hot neutral ground, with ground and neutral being isolated from each other in the sub panel. – Ed Beal May 1 at 15:45
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Same building, just supply ground and neutral in appropriate sizes and separate, and be sure that ground and neutral are not bonded in the sub-panel.

6AWG copper (as a cable, which typically limits you to the 60C rating...) is maybe pushing it a bit depending how loaded that 60A panel is.

  • It’s for a specific item The MCA is only 31A on the tag (3 ton) And the short heavy load startup only needs a 40a breaker it’s for a dehumidifier. So I think I’ll be fine even st the 100 foot run? Thanks for the help. The other few slots will be for smaller misc stuff I may need on the roof at a later date. – James Apr 30 at 21:52

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