Need to install a sub-panel off a 200amp service main panel that will be situated next to each other via 1" pvc conduit from bottom of each. The sub-panel is being installed to accommodate/supply a new hot tub with the manufacturer's recommended 50amp feed. And yes, there is a shut-off box (w/50amp GFCI breaker) being installed 6 foot away from hot tub and completely in line of sight. And yes, I know not to bond the sub.

A couple of questions: 1) Since main is full, I need to remove 2 (probably) breakers currently in the main panel to be relocated to the sub-panel to allow a 70amp breaker as feed for (and shut-off for) the new sub-panel. Is #6 THHN large enough, or would #4 be preferred, figuring the four wires needed, i.e. red, black, white and green?

2) Also, since the removal of the 2 breakers from the main (allowing space for the "feed" breaker) will reside in the sub-panel, am I allowed (with code and safety in mind), to add more same gauge wire length to the wires via wire nuts to reach the new location in the sub-panel?

3) I'm under the impression that the new sub-panel will not need its own ground rod due to its location to the main. I'm also under the impression that the hot tub shut-off box should probably have a ground rod of its own. This area, up on the side of a mountain is notorious and horrific, at best, for any kind of digging or attempting to drive an 8 foot stick in the very rocky ground. Is there anything else that can be done to duplicate what a ground rod would do that is considered acceptable?

Thanks for any and all responses!

  • Use EMT conduit. It's not any harder to install, and it's a legal ground path, so one less wire. Jun 14, 2017 at 0:04
  • Ok code geeks, if he has 2-3? relocated 20A circuits also traveling in the the 1" conduit, will he have to derate the #4 supply cable? Jun 14, 2017 at 0:08
  • 1
    @Harper -- nope! 310.15(B)(3)(a) point 2 excepts raceways shorter than 24" from the need to derate due to conductor fill Jun 14, 2017 at 22:47

2 Answers 2

  1. Number 6 AWG can be protected at 70 amps if the equipment at both ends is rated for 75°C yes to your wire colors.
  2. Yes
  3. If the new sub is attached to the main or right next to it, it does not need a ground rod. The NEC requires a grounding electrode at a separate building or structure containing more than one branch circuit. The single circuit to the hot tub does not require a ground rod. The equipment goundung conductor with the circuit is sufficient.

Nipples between panels of 24" or less do not require you to derate the wire ampacity.

When attaching a sub-panel I would not limit myself to 1" conduit. I would use a 1 1\2" or 2" nipple to allow more wire to pass between the panels. Just a personal preference though.

Good luck and stay safe!

  • is spot on. The only thing I would like to add is you don't have to Use the 1" nipple for additional branch circuits you could just use NM. Unless you live in an area that requires a conduit system in a residential dwelling. Jun 14, 2017 at 12:38

Dealing with your questions in turn here:

  1. You'll need 6AWG for the hots and neutral here -- that can carry 65A at 75°C, but you're permitted to round up to 70A by NEC 240.4 as 65A breakers don't exist. The ground should be 8AWG bare copper though as the feeder breaker is a 70A unit -- this is permitted by Table 250.122 and also saves you some valuable conduit space. (Put in the biggest conduit you can, by the way -- makes your life easier down the road.)

  2. Splicing in panels is A-OK if you have the space, which you very likely do. See NEC 312.8 for details.

  3. You are correct that the new sub won't need a ground rod as it's in/on the same structure as the main panel. As to the hot tub shutoff box -- it doesn't need a ground rod either as even if the hot tub is considered a "building or structure" for the purposes of 250.32, it falls under the Exception to that passage as there's only a single branch circuit feeding it.

  • #6 is rated for 65 amps but can be protected at the next higher standard rating which is 70 amps. As long as the calculated load does not exceed 65 amps.
    – ArchonOSX
    Jun 15, 2017 at 8:49
  • NEC reference is 240.4(B)
    – ArchonOSX
    Jun 15, 2017 at 8:55

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