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I need to add a 90A double-pole breaker to the service panel on my house to feed a subpanel in a detached garage. It is a GE that uses Q-line breakers. Looking at the current layout, I'm not sure it can be done. I've had a few electricians say it is possible to make room, whereas others have indicated a subpanel is needed next to this one.

service panel

It looks like there is a half-space available under the heat pump breakers. I was considering replacing the dishwasher and microwave breakers with a 15A tandem breaker, but this would only free up 1.5 slots total. The full size breakers in the upper left portion are AFCI. I don't think I can replace these with tandem breakers and still remain in code even if I replace the receptacles with the AFCI type.

Is there any way to accomplish this without needing to add a subpanel?

  • What edition of the NEC is your jurisdiction on? (I ask because AFCI requirements vary, which will impact the future life of this loadcenter) – ThreePhaseEel May 18 '18 at 0:07
  • OP can still off-beat-double-stuff 3 more 2-pole breakers, liberating 3 more whole spaces. And most 120V circuits are already xFCI. So OP has a little breathing room. Still, not a good place to be. @threephaseeel – Harper May 18 '18 at 1:05
  • @Harper -- yeah, he has exactly enough effective spaces free but not enough actual free space under 2017 code (because THQP, and the last remaining slot getting split across two 1/2" spaces) – ThreePhaseEel May 18 '18 at 2:11
  • @ThreePhaseEel -- We're on NEC 2014 currently, but NEC 2017 effective June 12. I take it I need to get this installed and inspected before then? – Volcano May 18 '18 at 21:06
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Ah, the tricky GE Qline.

  1. Convert the dishwasher to a 1-pole double-stuff breaker set low in the space.
  2. Pop off the cover above it. Now you have 1 space but it's a half space off-beat.
  3. Get a unique Qline double-stuff 2-pole 30A breaker, that is 1" wide and made to go in off -beat spaces. (And they require the off-beat, they can only work there).
  4. Move the water heater to that breaker.
  5. Voila, 2 full spaces freed. Use that for your 90.
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Getting this panel up to current Code

While Harper's solution gets you the free slots you need right now, your AHJ may insist that this panel be brought up to the current Code (at the moment, 2014) in your jurisdiction since you're touching it -- provided you are installed/inspected before the adoption date of the 2017 NEC in your jurisdiction, the 2014 NEC will apply.

What this means for you is that several of your breakers will have to be shuffled around, as the kitchen and laundry (washer) need AFCI protection now under the 2014 NEC. In particular, instead of what Harper suggests:

  • The current well pump breaker needs to be replaced with a pair of THQP115s that go in the outer half-slots there and are handle-tied with a THT2 handle tie.
  • The range breaker gets moved from its current slot to between the two halves of the new well pump breaker
  • The current dryer breaker is replaced with a THQP230 in the inner pair of half-slots in its current location
  • The current water heater breaker is replaced with a pair of THQP130s in the outer half-slots of the current dryer breaker's location, handle-tied with a THT2 again
  • The current kitchen and washer breakers get replaced with THQL1120AF2s
  • The current dishwasher and microwave breakers get replaced with THQL1115AF2s
  • And the THQL2190 goes where the water heater breaker was.

When 2017 NEC hits...

The 2017 NEC extended AFCI protection to all dwelling unit outlets -- for you, this means that beyond the kitchen outlets (countertop/SABC, microwave, dishwasher) and the laundry circuit requiring AFCI protection, the bathroom receptacles circuit also requires AFCI protection, which stretches your panel just past the limits if your AHJ insists that the panel be brought up to the 2017 NEC standards.

What I'd do in this case is get a decent sized NEMA 3R main lug subpanel with a ground bar -- a TLM2412RCU with a TGK24 ground bar will do if you want to stay in GE Q-line, although I prefer Siemens or Eaton BR instead -- and remove the existing bathroom breaker, replace the existing heat pump breaker with two THQP135s handle tied with yet another THT2 (presuming that the heat pump is a 240V-only load, as most are) in the slots around the current heat pump breaker, re-use the now-former heat pump breaker for the feeder to the subpanel, and then feed the subpanel with some #8 THHNs (hot/hot/neutral) in a fat metal conduit (such as 2").

The existing bathroom homerun then gets rerouted (it can pass through the existing panel to reach the new subpanel, as 312.8 permits splicing in electrical panels) to a 20A 1-pole AFCI that matches the panel's type (THQL1120AF2 if you went GE for the sub) in the new subpanel.

A third option -- nested subpanels

The third and final option would be to fatten up the feeder breaker Harper suggests somewhat, probably to 125A, and then install a subpanel next to your existing panel, fed off that 125A breaker, with a 90A breaker in the subpanel that feeds the garage. Again, running the feeder between the two house panels in fat conduit is a wise idea, and you're again not restricted to GE for the subpanel here. This would then let you move some of the house circuits into the new subpanel, where they'd have enough room for full-sized breakers.

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