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I am installing a 60 AMP sub-panel (GE TLM2412CCUP) and want to confirm the wiring and set-up before I set everything up. The pictures show the main panel (currently 60AMP as well but will be updated next year 100AMP or 125AMP), the sub-panel and all the planed wires (hand drawn). The wires are THHN and go through 3/4’’ EMT and FMC over about 40'. A couple of questions:

  • Main panel: location of neutral and ground wires for sub-panel is correct, right? They go to the same neutral/ground bar because they are connected on the main.
  • Sub-panel: No bounding screw, I installed a separate ground bar (GE TGK32CP), converted to main breaker panel (with GE TQMH000). All looks good? I don't like that there is not a lot of space around the ground bar. I guess, an alternative might be to use the right and left neutral bar for neutral and ground by disconnecting them but that creates problems with pigtails of afci breakers.
  • Ground wire: Currently, I have 8 AWG but I am thinking using 10 AWG instead. Any reason to stick with 8 AWG? The ground wire will support the 60 AMP panel plus two separate 15AMP circuits in the same conduit (or one 20AMP circuit instead).

Thanks!

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Your main panel

I gather your breaker in the upper left corner of the main panel, yes? Your breaker is back-fed, and is 60A. Since your main is the same rating as your subpanel feeder, you don't actually need a feed breaker in the main panel. You can just grab the subfeed lugs at the top of the panel. That will free up 2 spaces.

You will need the 2 spaces if you upsize the main panel's main breaker to 125A, but then, you'll also need a 60A feed breaker at that point. At that point you will hit stab limits on the stabs that the main breaker is clamped to; i.e. You won't be able to have any breakers across from the main breaker because the stabs can only carry 125A, and the main will absorb it all. However, those forbidden spaces can be used for a generator interlock, if you had any thoughts to that.

Three of your breakers look like Siemens, Murray or ITE. Those are alien breakers in this panel, and they must go, presuming this is a GE panel. They will not fit the bus properly. The only non-GE breaker I am aware of that can fit that panel is Eaton CL. If you need shunt-trip or remote on/off capability, Eaton CL has that.

Grounds

They make smaller ground bars that may fit in the ample wire bending space at the top and bottom. All neutrals should be brought to their breaker for AFCI/GFCI reasons. All wires should be cut long enough to reach any location in the panel.

If you can run the conduit entirely in EMT, you don't need a ground wire. However if you have one, think future and go #8. You might upsize the wire in the future, and why buy the ground wire twice?

Your subpanel does not need a main breaker if it's in the same building. If it is in an outbuilding, you need a disconnect switch, and the breaker will suffice but its size doen't matter. So there is no earthly reason to change out that subpanel main breaker.

Getting the most out of conduit

Conduit fill: you can get more than 60A out of #6 in conduit.

  • You can run THHN at the 75C column (65A rounding up to 70A breaker) if terminations at both ends are rated for 75C, which breakers are.
  • However you are capped off at 80% of its 90C rating (75A) giving 60A, because you have other circuits in the pipe.

If you can find a way to get those other two circuits out of that pipe, you can use a 70A breaker on the feed.

I would also consider larger than 3/4" sized conduit, to empower a switch to aluminum wire and future upsize. At 60A+ copper is a waste of money. Aluminum's bad reputation is inapplicable to these large sizes; and an AA-1350 feeder would be perfectly fine. That's outlawed today; now you get AA-8000.

  • Thanks! There is a main breaker on the main panel because it's a condo with 200AMP service in the house. 1) I rather stick with the two breakers for the new sub. On the main, I plan to add a main breaker mounting base (GE TQMH000) when we upgrade to 100/125AMP. That is going to free up two spaces. I like the breaker on the sub because it's on the 3rd floor. Any problems with this setup compared to your suggested changes? 2) I will get rid of the alien breakers. They are from the prev owner. 3) I will just run sub panel through the conduit (no extra circuits). 8 or 10AWG ground? – user2503795 Nov 17 '19 at 23:38
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    @user2503795 Right, you want the breaker on the sub because you think it'll preferentially trip locally and save you a stair climb. It will not. First, it won't be a problem; if you're not already getting regular main-breaker trips, you're not likely to start. Second, no way. Main breakers tend to have a bit more forgiving trip curve than branch circuit breakers, so it'll trip downstairs. Everytime. To great annoyance if it ever happened, which it won't. Ground: #8 for future expansion, or skip it if you have all-EMT. – Harper - Reinstate Monica Nov 18 '19 at 0:55
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    Thanks. Will do 8AWG ground. The reason for the breaker on the sub is more that I can shut down the power when I add circuits to the sub-panel etc.without going down... – user2503795 Nov 18 '19 at 1:00
  • @user2503795 -- understandable on the local shutoff – ThreePhaseEel Nov 18 '19 at 2:02
  • Thanks again for the hint about the alien breakers. I think it looks like ALL except the 4 recently changed afci breakers are alien. 3 are Murray and 7 are Square D. – user2503795 Nov 18 '19 at 14:19

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