Tandem breakers on a Square D QO panel

Old 01-04-04, 11:34 AM
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Tandem breakers on a Square D QO panel

I have a 100 amp Square D QO main panel on my raised ranch house built in 1969. I have already used up all the spaces in the panel and need to add another circuit for some outside lighting and receptacles.

I bought two tandem breakers to free up some space but the part that mounts on the pan rail has a hook on it instead of the tangs you see on a normal QO breaker. Looked on the square D website and it says these have to be mounted in positions on the pan rail that have a slot. Can't really tell without popping out breakers on my panel to see if the slots are there. Do panels this old have them or do I need to come up with another plan for adding this circuit?

I have one 20 amp circuit that I added into my garage for my compressor but really don't want to add it to that unless absolutely necessary.

One other question, the neutrals and grounds in my panel go to the same buss bar, will that effect the GFI breaker????
Old 01-04-04, 11:56 AM
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What is the model number of your panel?

Neutrals and grounding wires on the same bar in the panel that houses the main disconnect is fine. As long as you connect the neutral of the GFCI circuit to the GFCI breaker, the other neutrals will not interfere with the correct GFCI operation.
Old 01-04-04, 12:33 PM
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Panel is a QO 20M Series E1 Any idea if this panels pan rails have slots for mounting tandem breakers? Can't tell right now without taking some breakers out.
Old 01-04-04, 03:43 PM
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Square D uses two types of tandem breakers, the kind with the hook, like you bought, and the kind that just snaps onto the mounting rail. If I remember correctly, the kind with the hook is actually the cheaper of the two.

The hook-type tandem is for use in larger panels with 30 or 40 breaker spaces to prevent you from exceeding the code limit of 42 circuits in the panel.

My QO panel is an early 70's model and it does not have the slots in the mounting rails for the newer tandems. It only has about 20 spaces, so even if you installed tandems in all the positions, you couldn't exceed 42 circuits.

If you check the circuit listing on the inside of your panel's door, you should see some spaces are divided with a dashed line. Those are the spaces you can put the tandems in. If your panel is similar to mine, you'll need to return those "CTL" style tandems and pick up the other style without the hook.
Old 01-04-04, 04:50 PM
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That's funny, I have 20 positions on mine too but it says to USE the CTL style breakers. House will built in 1969.
Old 01-04-04, 04:51 PM
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hotarc are you using any tandems in your QO panel and if so where did you get them?
Old 01-04-04, 06:11 PM
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Yes, I've got a bunch of tandems actually. In fact the original 1974 installer used 5 tandem breakers to begin with. Too bad they didn't just put in a larger panel. I have since added a newer tandem breaker to the panel as well. It was purchased from Home Depot.

If I remember correctly the tandem for my panel, with the standard QO mounts, was about $20 and the newer style, with the hook, was like $10-12. I just looked at Home Depot's website and they appear to have two different QO tandems, one for $15, the other is $25. So I assume the one for $25 is for the older panels.

Anyway, if your panel says to use CTL style breakers, maybe you do have the slots in the mounting rails. Does the chart on the inside of the door have dashed lines dividing some of the spaces?
Old 01-04-04, 06:15 PM
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Generally 100 amp panels can have a maximum of 24 single pole pspaces. A panel with 20 spots but a capacity of 24 circuits is known as a 20/24 panel.
You should be able to install 4 twin breakers in your panel.
Look at the circuit directory. Do the bottom 4 spaces have a dotted line spearating the upper and lower half of the label for each space?

EDIT: Hotarc types faster than me
Old 01-05-04, 04:22 AM
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Nope, no dotted lines. My local Home Depot only had the ones with the hooks, will try stopping by Lowes today to see if they have any.

I don't want to shut the power down only to find out that I have the wrong breakers (hook type).
Old 01-05-04, 05:20 PM
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Back again guys. Found the QO2020CP breaker I needed at Lowes this afternoon. Put it in tonite and everything worked out fine.

Installed a GFI breaker in the open slot for the circuit I ran out to my shed. Flipped everything on a everything works fine like I wanted.

Funny thing is, I emailed square D about this panel and they said I could not add tandem breakers to it!? What's up with that? Below is the email they sent. Why wouldn't it be able to accept tandem breakers???


Dear Mark Hueffman:
Thank you for your internet inquiry!
We regret to advise you that cat. no. QO20M cannot accept any tandem circuit breakers.
Hope this helps! If you have any further questions or concerns, please do not hesitate to
contact us.
Very truly yours,
Dave Wilson
Staff Product Support Specialist
Customer Information Center
PH: 1 888 SQUARE D
[1 888 778 2733]

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