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Old 01-25-2008, 09:43 PM   #1
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using twin/half breakers

I have a cutler hammer box with 30 slots 200amp main I cannot determine max circuits. Since it is a CTL box if the circut max is 30 then the 1/2 breakers should not fit on a slot. Is my logic correct in assuming this?


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Old 01-25-2008, 10:44 PM   #2
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Hi Don

Lighting and Appliance Panelboards (load centers) have been marked "Class CTL Panelboard" (CTL = circuit total limiting) since the late 1960's. Some of these CTL load centers will accept a breaker called a tandem. GE panelboards use two 1/2" breakers instead of a single molded case tandem. These breakers have varying means to limit the number of them that can be installed in the load center. Cutler hammer CH has a hooked foot on the tail end of the tandem breaker that must mate up with a slot in the load center-mounting rail and has a rejection feature in the nose of the breaker that must have a notch in the bus stab in order to connect it. Others use a rejection feature in the breaker that must mount up with a fork or L - slot in the busbar to be installed.

When you hear somebody talk about a 30-40 load center . It has 30 spaces for full size breakers and 10 of those spaces have slots to that allow the installation of tandems or two 1/2 size breakers. This 30-40 load center can contain 30 full size breakers and no tandem breakers, or it can contain 20 full size breakers with 10 tandems breakers for a total of 40 circuits.

These tandem or 1/2 size breakers cannot be installed in a panelboard that that does not contain a "slot" in the mounting rail or a fork or L-slot or tabs the busbar, or some other means to allow their connection to the bus and rail.. So the CTL panelboard has a physical means in the panel configuration to prevent the installation of more overcurrent devices than that number for which the panelboard was listed. A panel board for instance that states 3030 or just 30 in the model number will not accept tandems. However if you don't know your panel model # you need to look at a tandem for your panel and then the panel to see if the rejection feature is present to prevent the tandem from being installed

Below is a cutler hammer ch tandem....

The second image is a cutler hammer tandem BR circuit breaker showing notched bus stab and rejection feature in the breaker

The third image is the CH load center with both a full size and a tandem installed notice the hooked foot goes over and under the rail and the rejection feature is on the nose of the breaker.

The last image shows the differences between ch and br cutler hammer breakers and how they install in their appropriate center.

You can click on the black and white thumbnails to enlarge the image

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using twin/half breakers-tandem-breaker-rejection-feature.jpg  
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Last edited by Stubbie; 01-26-2008 at 12:46 AM. Reason: fix my spellin
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