8

Question

I'm scratching my head trying to understand why my Sub Panel was set up using the tandem breaker configuration described (with picture) below.

There are 3 tandem breakers, with the top two on the top breaker slot and the 3rd breaker on the next slot down. You can also see a cover where another tandem breaker for the second slot might normally be. There's also what I believe is a "cheater bar" across the bottom two breakers tying them together.

Why are the bottom two tandem breakers tied together across two slots like this? And, possibly worse, why is there another non-joined tandem breaker sharing the top slot. Best case this is some complicated scenario I just don't understand. Worst case this is a problem and I need to re-wire my subpanel (which I might do anyways for sanity).

Background

I understand tandem breakers allow you to use the same breaker slot for multiple circuits (with caveats). I also understand that you can tie multiple breaker slots together to control phasing or create a 220v circuit.

However I can't quite make sense of what's happening here. There aren't any 220v circuits that I'm aware of and that'd be a problem anyways as these are 15A breakers, wouldn't it? I can see 4-5 separate circuits in my garage attic which are all tied to these two breakers. Note the circuits aren't under heavy load: a few lights, 1 outlet and the garage door opener. I haven't looked yet to see if all of these circuits go directly to the breaker or if there's a junction box hidden somewhere in my house.

Maybe I'll pull off my panel cover and discover some weirdness on my panel itself leading to this setup, but this configuration seems suspicious. And there's so much room on this panel. I don't understand why tandem breakers were even necessary.

It's also possible that the cheater bar is there purely to turn off all power to the garage if either breaker is tripped, maybe as a safety feature.

Any thoughts?

Thanks!

Tandem Breakers

2
  • 3
    The three breakers are not "tandem breakers". They are plain vanilla single-pole breakers. The second and third breakers are tied together with a tie-bar, effectively creating a single tandem breaker. This arrangement takes advantage of the fact that, on your typical 220v panel, the slots alternate from one pole to the other, so that any two adjacent full-sized breakers will be on opposite poles. – Hot Licks Apr 19 at 1:35
  • 9
    Aside - if something goes out in the garage and you're running machinery, having the lights go out as well is suboptimal. The inertia of the tool will generally keep it moving, and you can't see that in the dark. I have seen workshops set up with emergency lights that come on as soon as mains power goes off. You don't want to tough the sharp spinamathingy of extreme mangling in the dark by accident. If its just a car park, that's a different matter. – Criggie Apr 19 at 1:42
9

A pic of the innards of the panel would help, but it's mostly likely a MWBC (Multi Wire Branch circuit) for your garage lights. If so, it's required that the breakers feeding it are handle tied like in your picture. Seems like over-kill for a lighting circuit unless there were lots of high wattage incandescent lamps in the original installation.

7
  • Thanks! After doing some more research this looks like it's probably the right answer. Going to mark as such for now. I'll follow up once I've taken the panel off and can see what's happening underneath. The light fixtures were originally incandescent, this certainly could be the reason. – Aaron Apr 18 at 16:15
  • The 1st tandem breaker sharing the top slot is still concerning though. I suppose this means that the neutral for the top slot must be connected to the 1st tandem breaker ("OUT GFI") and the 2nd two breakers are sharing the neutral for the 2nd slot ("GARAGE LIGHTS"). Otherwise this configuration defeats the purpose of the breaker tie for a MWBC circuit, which is to ensure that all power to the circuits sharing the neutral is cut when the joined breaker is flipped to off. I think? I'll have to take the panel off to confirm. Thanks! – Aaron Apr 18 at 16:31
  • 1
    @Aaron -- don't worry about the neutrals – ThreePhaseEel Apr 18 at 16:59
  • 1
    Yes, I'd like to see some pics of the panel with the cover off. I often worry about MWBC because if they aren't done correctly, or somebody fiddled with it and the 2 breakers are on the same phase (leg) you can severely overload the neutral. If you have a meter and are confident in doing this, measure the voltage across the handle tied breakers, it should be roughly 240v. If zero (or close), they are on the same leg and that's a problem. When you post additional pics, please EDIT your question to include the pics....don't post a separate question. – George Anderson Apr 18 at 18:49
  • 2
    @Aaron Neutrals don't connect to breakers, they connect to neutral bars. Note this is a GE panel, where the breakable cover plate represent a space, and with these half-height breakers it's 2 breakers per space. Each space is on the opposite phase. Space 1 is the single and half the double. Space 2 is half the double and the blank cover. – Harper - Reinstate Monica Apr 18 at 21:00
15

GE does things differently

Since it appears you have a GE panel with GE breakers in it, your situation is a bit different than most folks. What you see there aren't "tandem" breakers at all, but half-width "double-stuff" breakers (THQP) instead, with the top breaker independent and the bottom two breakers handle-tied to feed a multi-wire branch circuit. A filler plate was then used to keep stray fingers out of the remaining half-space.

This means that the MWBC has a neutral wire landing on one neutral screw in the panel, and the outdoor lights circuit then has its own neutral wire landing on a different neutral screw in the panel. As to why it was done this way? It was probably done this way simply because the installer had THQPs handy instead of THQLs; there's not really much to be concerned with about that, although occasionally a THQP will wind up losing its grip on the bus a bit and becoming wobbly as a result, which can be fixed simply by replacing the breaker.

4

Sometimes the NEC uses the term "lighting" in a broad manner that includes receptacle outlets, it is possible that the ran multiple circuits as a MWBC (two hots sharing a neutral).

The use of tandems does seem unnecessary, it could be a case of planning for the future, or just a case of smoking-what-you-brought rather than buying different parts to accomplish the same thing. For instance when adding a sub-panel to a crowded main panel I typically use the existing brand so I can move the existing breakers to the new panel if needed.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.