Is it permissible to land two wires on one screw (pole) of a 120/240 two pole breaker ....
I know that the 120/240 rated breaker is rated to supply line to neutral loads but am I in violation by supplying both line to line and line to neutral loads? Manufacturers get away with this all the time because a lot of appliances are listed as a single unit. ....
It is only permissible to land two wires under a single screw if the device (or connector) is listed for that. The UL White book has a catchall classification called
ELECTRICAL EQUIPMENT FOR USE IN ORDINARY LOCATIONS (AALZ) which is referenced by most other classifications (including breakers), For screw terminations it states the following:
Terminals ? Product terminals, including wire connectors and terminal screws, are acceptable for connection of only one conductor, unless there is marking or a wiring diagram indicating the number of conductors which may be connected.
AALZ has lots of good stuff in it. You should download the White Book from UL.com.
As to the question about L-L and L-N loads:
100 Utilization Equipment. Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes.
A unit outhouse may meet this definition. But most utilization equipments are things that are not designed to hold a person.
210.4 Multiwire Branch Circuits.
....
(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where the branch circuit originates.
Informational Note: See
240.15(B) for information on the use of single-pole circuit breakers as the disconnecting means.
(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1:
A multiwire branch circuit that supplies only one utilization equipment.
Exception No. 2:
Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.
240.15 Ungrounded Conductors.
....
(B) Circuit Breaker as Overcurrent Device. Circuit breakers
shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), (B)(3), and (B)(4).
(1) Multiwire Branch Circuits.
Individual single-pole circuit breakers, with identified handles tie, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve
only single-phase line-to-neutral loads.
So unless you want to apply exception no. 1, you need a breaker marked "common trip".
Using a common-trip breaker is the safest course.