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I want to install a sub panel to my GE split bus panel. The diagram indicates that I could replace the two full sized 2-pole breakers (2 inch wide each) on the upper left with three compact 2-pole breakers (1 inch wide each). The diagram indicates that this is not an option on the top right.

I would use 30 A and two 40 A compact 2-pole breakers for the dryer, a/c condensing unit, and the range. I would use the existing 50 A breaker on the top right for the sub panel, unless I should go larger.GE split bus panel cropped pic of sticker

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EDIT On the right from top the 120 V branch circuits are: 15 A -- bdrm 2,3,4 E. wall receptacles, 2 closets single bulbs, 20 A (switched off) for dishwasher but not installed, 20 A garage receptacle, lights, door opener, 20 A ceiling fans, lights, 20 A GFCI kitchen counter, 20 A clothes washer, 20 A refrigerator and 1 kitchen receptacle not near sink

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  • Is there a main disconnecting means upstream of this panel already?
    – ThreePhaseEel
    Jul 7, 2018 at 21:18
  • Also, what size is your range? (in kW)
    – ThreePhaseEel
    Jul 7, 2018 at 21:22
  • The installation instructions for our 30 inch GE range with one oven specify a 40 A breaker. Sticker states 13.3 kw at 240 V. Doesn't seem to match?! The Vent-a-Hood is on a separate circuit. The original range had two ovens and exhaust hood all on one 50 A breaker. It didn't occur to me to change the breaker when I installed the new oven 25 years ago.
    – Jim Stewart
    Jul 7, 2018 at 21:38
  • There is no disconnecting means upstream of this panel, at least that is accessible to me, that I know of. The panel is inside the garage on an exterior wall.
    – Jim Stewart
    Jul 7, 2018 at 21:45
  • the NEC 220.55 demand factor rules explain why the kilowattage on the range doesn't match the breaker size specified by the manufacturer. As to the panel -- I'll have to get back to you on Monday about it, as there are several issues here that I'll need GE tech support's input for.
    – ThreePhaseEel
    Jul 7, 2018 at 21:51

3 Answers 3

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No one has posted an answer for this question, so I thought I would take a stab at it and remember some of it is more about code intent rather than written law.

First, you have a split bus panel. This panel was developed because of a loophole in the early code that stated you could have 6 means of disconnect to disconnect totally from a service (the 6 disconnect rule). So manufacturers decided that instead of paying for an expensive(?) main breaker, they would instead create a panel with six means of disconnects, diversifying the load and using lower priced smaller breaker for disconnecting purposes. Like I said it was a loophole, which was caught by the NEC and then immediately corrected. That is why there is a very small time line where these panels were used, because they are now illegal.

Now that you have a brief history let's get to your question. You panel was installed when it was legal to do so, and it can stay that way under the grandfather clause. Since it was a generic panel, the installer could have used all of its capacity (6 disconnects) but didn't. You now want to upgrade your panel to its full capacity by adding breakers.

Now here is where the intent of the code affects the answer. When you remove and add breakers to this panel, you are modifying a panel. When you modify a panel you must bring it up to the updated code and if you can't do that with the existing panel, you should replace it. In other words the panel was installed during a time where it was legal to do so, but you can't "grandfather" in an upgrade.

Now I know this could be a big discussion and a lot of it depends on each persons interpretation of the NEC. I will say it really doesn't matter what any ones opinion is, including mine. The only one who's opinion and interpretation counts is the AHJ. That is what they are there for, and that is what they do. Most people hesitate to go the the AHJ because they fear they will rule without considering cost or other installation problems, and they will probably want to inspect the work after it is done. Then again that'is what they are paid to do.

Hope this helps and good luck.

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  • I appreciate your opinion and I will check with my AHJ before I do anything. The house was originally wired in aluminum (don't know alloy) except for the cable to the a/c condensing unit which is solid copper #8. The dryer and range are multi-stranded Al. The 15 A circuits are in #12 and the 20 A in #10. When I pig-tailed the receptacles and switches 38 years ago I got a permit and had the job inspected. Later I added two new 20 A circuits in #12 copper, but didn't get a permit because at the time I thought one wasn't required.
    – Jim Stewart
    Jul 9, 2018 at 17:34
  • Seems like you have won the trifecta of electrical wiring. Now all you have to do is declare the house was also wired in BX.
    – Retired Master Electrician
    Jul 9, 2018 at 21:56
  • How do I tell whether my service drop wires are large enough to sustain an upgrade from 150 A to 200 A service?
    – Jim Stewart
    Jul 10, 2018 at 0:39
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    @JimStewart that's a whole another can of worms, probably worth a separate question as there are multiple pieces to it.
    – ThreePhaseEel
    Jul 10, 2018 at 1:07
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While you technically could do what you describe

While what you describe is possible with suitable THQP2xx breakers and a couple of half-width filler plates...

this panel's just a pain in the rump and probably should be replaced

split-bus panels are a pain in the rump, as they can't be brought up to modern standards. Yours likely does not support the THQLRK or TQDLRK required for conversion to a backfed main breaker configuration (I finally spoke with a human being at GEIS/ABB about this, and they couldn't say definitively, but were skeptical of the panel accepting a backfed main retainer), and you are two slots short of the space required to wrangle a TQDL21150 into your panel without bumping a circuit off to the subpanel, even with tapping the feeder to the sub off using the main lugs of the panel.

Replacing it with a modern panel would be the best move should you desire more from your electrical service -- make sure you don't short yourself on breaker spaces ever again, though! (A 54 or 60 space panel is by no means out of place here.)

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  • Thanks for your research effort. I am going to check with City of Dallas electrical Inspection to see what they will let me do. If they would let me put in a sub-panel to this GE split bus panel, I can definitely do this myself, I would hope without having the meter pulled. In my experience in my neighborhood when houses are sold the buyers are factoring in that they will be doing a lot of electrical upgrading. I can live with the current set-up right now, as is, and if we would get an EV it would not be one that requires a high current charging station.
    – Jim Stewart
    Jul 11, 2018 at 0:02
  • How would I tap the feeder to the sub from the main lugs? I assumed I would use a 2-pole breaker in one pair the top slots. Would this be called tapping the main lugs?
    – Jim Stewart
    Jul 12, 2018 at 0:01
  • @JimStewart -- a main lug or split bus panel that has been fitted with a backfed main breaker has nothing hooked up to the main lugs normally, but nothing stops you from connecting a feeder to the lugs at that point as they're on the load side of the main breaker. It's not a "double tap" because there'd be only one wire in the lug at that point, although it may be a feeder tap if the feeder wires are smaller than the main breaker, and those have a whole bunch of special Code rules surrounding them.
    – ThreePhaseEel
    Jul 12, 2018 at 0:06
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The Code does not address using a split bus load center to feed another panel board. The 2017 NEC is silent on this application.

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  • It is generally silent on that front, yes, but there are specific issues with the OP's hardware that make subpanel installation difficult for them.
    – ThreePhaseEel
    Aug 19, 2019 at 22:53

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