Would anyone mind to validate/assuage my concerns as marked on the image here? Even after some research I'm hesitant on #1 (maths) and #2 (best practice vs. code requirements). And of course if anything else is glaringly alarming I would love to hear it. At this point I'm mentally/fiscally prepared to run new feed lines and upgrade the first subpanel.


Edit: transcribing concerns from image (thank you Freeman):

  1. Outbuilding subpanels are fed via a 50-amp breaker and 8-gauge UF copper from the main panel. This wire is too small to be protected by that size breaker, correct?
  2. The feed lines for a 2nd subpanel are double-tapped into the 1st subpanel's lugs instead of a being supplied from a breaker; was this an unsafe shortcut?
  3. Outdoor subpanel has an NM ground wire attached to the neutral bar.
  4. Outdoor subpanels do not have a grounding rod.
  • 1
    I'm not sure about #1, but you're right to be concerned about 2-4. Also, it would be far better to put the actual concerns in text instead of an image. Some people use screen readers and your questions would come to them as "Layout".
    – FreeMan
    Dec 15, 2021 at 18:47
  • I'd agree with all the problems. My understanding is that 8 AWG copper is normally 40 (14 AWG = 15, 12 AWG = 20, 10 AWG = 30, 8 AWG = 40, 6 AWG = 50). Dec 15, 2021 at 20:00
  • In my state the inspector would hassle about using the 75 degree table for ampacity below 100a, it is actually a hidden in the masters exam if non motor and you use 75c table it’s wrong. Will #8 overheat with 50 amp? Not the wire it’s rated for 90c the connections are the question, older small panels are 65c rated. #2 double tapped, if the lug was listed for 2 wires there is no requirement for a second breaker as long as the wire is large enough. 3 gnd on the N buss is ok if built prior to 1999, they look separate, if in the same building no rod is required today, after 99 separate building
    – Ed Beal
    Dec 15, 2021 at 20:46
  • Ran out of room, it depends on the year built what was code! If you modify panel 1 panel 2 would need to be updated no grounds on the neutral bus, grounds on the ground bus like panel 1. The outer covering on the UF / or other NM type cables need to extend into the box 1/4” , I don’t think the square D lug is listed for 2 wire but check the sticker some older ones were,on the ground buss. I know there can be 2 grounds under 1 lug and possibly 3 but check the listing,( the sticker in the box on the side)
    – Ed Beal
    Dec 15, 2021 at 20:58
  • Thank you everyone for the input. It is very likely some of this work did take place 20+ years ago and meets those requirements. I am definitely looking into upgrading the feed lines and panel #1 with something bigger, so will correct those minor issues in panel #2 as well.
    – Jack
    Dec 16, 2021 at 14:22

2 Answers 2


The #8Cu UF cable is rated for only 40 amps. This is plainly stated in NEC 310.15(B)(16) - UF is clearly marked as rated only 60C thermal.

The subpanel lug is not rated for double-tapping, unless it says it is in the instructions or labeling.

You have 4-wire feeder, and that means you must separate neutral and ground in the subpanels. Completely. There needs to be a ground bar in that second one.

Outdoor subpanels need grounding rods.

These are all trivial fixes, and I would say you are code cpmpliant. Optional upgrades? The first thing I would do is replace the 2-space panel with something slightly larger, like a 30-space lol. Then you don't have to double-lug, you can just use a <=60A breaker to give you 2 more lugs. (Effectively using it as a subfeed lug kit; price both and you'll see why you'd use a breaker).

And by the way, Square D breakers do allow double-tapping up to a certain size of copper wire. (Ironically if the 2-space panel had been back-fed, it might be legal lol. Unfortunately it can't be, because you can't get tie-down kits for a 20 and a 15 breaker.)

Anyway, if you are sanguine with 40A and the feeder is installed properly, you are good to go. However, and particularly if either subpanel is near where someone might park a car, then I for one would upgrade that feeder to 2-2-2-4 aluminum. (90A). That will amply cover what you are powering now, and give about 60A of headroom for electric vehicle charging. You might not want, but your home-buyer might... and we're seeing them pay thousands extra for a house that is ready for level 2 charging.

The new gold standard for EV charging is 80-90A shared among all EVs using Charge2 technology. So if you are an EV maven, you might go bigger!

  • Thank you for all the feedback! I am definitely of the mindset of installing much more capacity than currently needed in order to keep future options open (for either myself or other owners). <br>A few follow-up questions if you don't mind...
    – Jack
    Dec 16, 2021 at 14:49
  • I'm still quite the electrical novice and have steered away from Al wire so far; I'll be doing plenty of reading too but is there anything critical that I should be aware of? I know from plumbing to keep different metals from direct contact, so I'm assuming the Al wire should be nowhere near exposed Cu. What about expansion (what I've heard most about Al is that it can wiggle itself free from connections)? Should I be routinely checking/tightening the subpanel lugs if they're handling Al wire?<br>Regarding EVs, have you seen any houses need to go to 400 amps to support it? (Currently 200 here)
    – Jack
    Dec 16, 2021 at 14:52
  • @Jack if you'll read any of Harper's answers, you'll see that modern AL wiring is 100% OK. The horror stories you've read about were from the 70s when AL wiring was used and installed incorrectly. Most modern devices are rated CuAL which means you can use either type wire in them, so long as you torque down the screws properly. Note, most feeder wire from the pole to the house is AL and all those silver bars in your panel are AL, too - AL wire is actually better in that case!
    – FreeMan
    Dec 16, 2021 at 15:22
  • That's great to know, thank you @FreeMan my brain might just be hung up on all those charred outlets when I'm just working with main lines (my locality wouldn't let me wire branches with Al anyway).
    – Jack
    Dec 16, 2021 at 16:17
  • @Jack avoid aluminum wiring for small 15-20A branch circuits. They're safe now after we learned the lessons, but home buyers don't like it. The top 2 lessons are "use terminals properly designed and labeled for AL wire" and "set screw torques with a torque wrench because they matter". (The latter was discovered with failing copper wires). With large feeder e.g. to subpanels, the lugs often are made of aluminum, because aluminum lugs play well with both wires. Dec 16, 2021 at 17:09
  1. Carrying a feed onward from one sub-panel to another isn't fundamentally wrong, as long as the wire and the second panel are adequately protected by the breaker that's feeding the whole setup.

However, this this case there is definitely the problem that those lugs are almost certainly not rated for two wires. The splicing needs to be done with appropriately listed splices, add-on lugs, feed-through lugs, etc.

Also, depending on where the two sub-panels are physically located in relation to the main panel and each other, they may constitute a violation of the "outbids must have a single local shutoff" rule.

  1. Not ideal and not legal for new installs, but may have been legal when installed. 3-wire feeds to sub panels (and combining neutrals and grounds on the same bar in the sub-panel) was legal till the mid-80s or 90s.
  • Thank you! I am pretty sure most of this panel work took place in the 90s which explains a few things. The subpanels are indeed in outbuildings, so would need those independent shutoffs and grounding rods. I'll just upgrade their size to accommodate proper chaining and avoid double lugs.
    – Jack
    Dec 16, 2021 at 14:57

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