Learning terminology

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Old 07-15-13, 04:56 AM
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Learning terminology

I've learned so much from this site and no one has put me down or used a condescending tone when answering my questions regardless of how stupid they sound.

So I have question regarding the terminology of breakers. I understand SPST (Single pole, single throw) breakers as well as DPST (Double or 2 Pole, Single Throw) breakers. However, I've read posts where people have run out of room in their service panels so they installed a "tandem breaker". Now, when I hear the word tandem, I vision a happy couple riding a tandem bike where one person is in front of the other. Or, I see big rigs pulling tandem trailers; one trailer in front of the other. How does this work in service panel? There isn't any room to put one behind the other. Plus, wouldn't this be dangerous? Please, clarify this for me. Thanks Roger
 
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Old 07-15-13, 05:16 AM
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Basically skinny little breaker switches squeezed into a single-width breaker for two circuits.

QOT1520 Tandem Plug-On Circuit Breaker | Square D | SuperBreakers.net

 
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Old 07-15-13, 05:21 AM
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Plus, wouldn't this be dangerous?
The only time it can be dangerous is when they are installed in a panel that is not rated to use tandem breakers. It is also a code violation.
 
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Old 07-15-13, 05:30 AM
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Tow_Guy; So, tandem doesn't mean end to end, it's side by side but sharing one "conventional" breaker slot. That makes sense. That link you provided helped me see it. Thanks for the lesson. Roger
 
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Old 07-15-13, 05:34 AM
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How would I know if they are/are not allowed in certain panels? Would that be stamped or identified somewhere on the panel?
 
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Old 07-15-13, 06:35 AM
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There should be a label on the inside of the door of the panel. However, sometimes the label is inside of the cabinet part of the panel. The label will show either a diagram that shows tandems are OK, or you need to research the part number.

For example a Siemens S3040B1200P is a single phase 30 space, 40 circuit 200 amp panel.
 
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Old 07-15-13, 07:51 AM
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So, tandem doesn't mean end to end, it's side by side but sharing one "conventional" breaker slot. That makes sense. That link you provided helped me see it.
Tandem can mean "end-to-end" or it can mean side-by-side". The picture at the link provided was a more recent Square D QO series tandem design. The older design of that same series breaker is slightly different. I suspect the design was changed to reduce cost in manufacturing.

Square D Type QO 20A 20 Amp Twin Tandem Circuit Breaker GUARANTEED!! QO2020 os on eBay!
 
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