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I've been reading posts but am still a little confused on this as each situation is slightly different and I am not familiar with the terminology.

Main breaker has two larger wires coming into it. The second one feeds a panel in the garage, which was an addition. Panel has 3 circuit breakers in it.

Here is picture. My home inspector mentioned it as a problem. Do I need to deal with this? enter image description here

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    What is your question? All you've done is show a picture. – Chenmunka Feb 26 '18 at 16:26
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    It's not enough. There are many potential questions, and the OP needs to pick one. Get well soon. Hope you found all the goo. – isherwood Feb 26 '18 at 16:47
  • A sub-panel should be fed from a breaker and not tied into the main lugs, but you know that because the home inspector told you, right? – JPhi1618 Feb 26 '18 at 16:48
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    @isherwood while I'm all in favor of using this as a teaching moment to teach OP how to use SE, I say we pick because one of them is much more urgent than the others. Regardless, he did pick - note words 3-4 of the title. – Harper Feb 26 '18 at 17:16
  • no, you do not need to deal with it. just call the home inspector and tell him/her that s/he is wrong .... what do you think? – jsotola Feb 26 '18 at 19:42
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My bet is your panel is full and someone wanted to add the shed subpanel anyways so they simply fed it into the utility connection to the panel. There's several problems here

  1. They're mixing aluminum and copper. This is dangerous because the wires can corrode like this. Corroded aluminum is a fire hazard
  2. There's no way to cut the subpanel off. I'm sure someone can quote the relevant NEC, but there's a few reasons you connect wires in the panel to a circuit breaker, and one of them is you want to be able to cut the power to that wire
  3. Even if the subpanel has a breaker, there's a risk that the wires double-tapped can exceed their design limits (which is the other major function of a breaker). If they do, the insulation can melt and now you have unrestricted current flowing straight from the utility, likely meaning fire.

If your panel is full, you'll want a subpanel by the main panel to hook this to. That likely means you'll need an electrician. It's a mess, but I wouldn't leave this as-is.

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    A sub would not require a breaker at the main panel if the wire size was the same as the main feeder, but cu /al under the same lug big no no even if listed for 2 wires. They make double lugs for this. – Ed Beal Feb 26 '18 at 19:07
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Other than everything @Machavity has said. It is illegal to tap more than one conductor to a lug unless that lug is designed to accept more than one conductor. Looking at your picture, I can tell you that that particular lug is not designed to accept more than one conductor.

Even if you replaced that lug, see everything else @Machavity has said.Meaning you still have many more problems that need to be corrected.

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The wire to the subpanel is too small

This is the biggest gotcha here.

Presumably there is a main breaker upstream of this point e.g. Outside. Breakers protect wires. It is sized to protect the fat aluminum wires coming to this panel. The wires to the sub are much smaller and the main breaker cannot protect them. This sort of daisy-chaining panels is legal but all the wires must be sized for the protecting breaker (or vice versa).

There is an even worse possiblility: that this is a split-bus "Rule of Six" panel, designed to h ave 6 main breakers in its top 12 spaces and those are the only breakers. In that case, the wires to the subpanel would have no protection whatsoever. Daisy-chaining like this should not be done on a Rule of Six panel.

Other problems

As you observe, the lugs are double-tapped. You can't do that. There are double lugs made for that purpose which provide 2 voids and 2 setscrews. That lets you set torque correctly for each wire type independently.

All the wires are white. You can't do that with wire 6 AWG or smaller. If the wire is larger than 6 AWG (doesn't look that way), you still have to mark the hots with black brown red orange yellow pink blue or violet tape or shrinkwrap. That won't matter because you have to pull the wires and replace them with correct wires.

The good news

The main wiring method is metal conduit, hence the notable lack of ground wires. The conduit is the ground. That makes it a lot easier to replace wrong wires. Generally main feeders like the one to the subpanel are aluminum, but depending on the size of the conduit, you may need to use copper wires to get wires small enough to be fill-table legal in the existing conduit.

To fix it

Start by making sure our assumptions about grounds are correct.

Next figure out where your main breaker is. If it's outside the house, we can entertain the idea of continuing the double-lugging concept:

  • look at the conduit for the subpanel wires and compare that with the conduit fill table. Given that conduit, what's the largest size of wire that will fit 3 in that conduit?

  • Look up that size on the wire ampacity table, and working out of the 60C columns, search for a "happy match" amongst your main breaker size, ampacity of wires that will fit in that conduit, and cost.

  • If can find a happy match, then replace that cable, and replace the lugs with double lugs. If you cannot, then daisy-chaining won't work.

If daisy-chaining can't work, then you need to move the subpanel wires to a 2-pole breaker actually in this panel, which means making space in this panel.

  • You do that by setting a new subpanel right next to this panel, and moving at least 4 spaces' worth of breakers over to the new near-subpanel. (If it's a split-bus Rule of Six panel, you need to free up these spaces in the top Rule of Six area). Then install the two 2-pole breakers, one for the near subpanel, one for the existing subpanel. Get a nice big subpanel so you never have this problem again.

If you haven't replaced the 3 white wires yet, now it's time to do that - 2 must be replaced with colored wires. Black-black or black-red will do, as will any legal "hot" color.

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