Tandem breakers

[Dpitch]

But if a two pole tandem is a quad and a quad is two duplex receptacles and the moon is closer than the sun. Then did the chicken come before the egg


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[jaggedben]

Ge makes a quad, it has 4 single pole breakers together just like a 2 pole has 2.
This is why you cannot use a single pole tandem for a MWBC, a double pole tandem you can actually have 2 mwbc so long as each is terminated on seperate poles.
Generically what is a 2 pole breaker? Generally we speak of a breaker that lands on 2 seperate buss tabs. What is a single pole breaker? Generally It is only landing onto one buss tab.
But I think mfg terminology also lend to some confusion. In some advertising the 2 pole tandem is also called a quad, but I have always seen the quad being like the 4 pole GE breaker below.

The way you are using pole is not consistent with how it is used for all other products in the electrical and electronics industry. Generically, a 2-pole switch or breaker or relay or contactor (etc.) opens or closes two independent electrical connections on the same handle, coil, trip mechanism or such. The manner of external connection is irrelevant. So 'generically' a 2-pole breaker can fit in any kind of space or have any connection to the bus as long as it has 2 sets of terminals on the same trip mechanism.

Examples:
-If I want a contactor to open the conductors connected to what you (not I) are calling a single pole tandem, I need a 2-pole contactor.
- GE has a skinny 2-pole breaker that can be connected to 1 or 2 busbars depending on how you place it, but it remains a 2-pole breaker regardless.
- Eaton and Sq-D make 3-pole switches that can be used for 3 conductors at 250VAC or for 1 conductor at 600VDC. In the latter case the two outside poles are used in series. But it's a 3-pole switch regardless.

'Tandem' and 'quad' are more colloquial than 'pole' but both Eaton and Siemens use 'quadplex' in their catalogs for the first picture you posted, not the second.

 

[jaggedben]

Also the Zinsco and Challenger examples tortuga mentioned above are both still examples of two single-pole breakers in one housing, even though they connect each breaker to a different busbar.