Thank you, and...
Thank you, and...
3: Those slash rated breakers meed the code requirement in the situation you describe as long as they connect only to the A and C phase buses. That way they can serve either an MWBC, single 120V loads or a simple line-to-line 240V load which is no more than 120V to ground on either end.
Are they safe? Sure, except to the extent that they serve as a bad example for somebody who later connects to the B phase for any reason.
The most safe and understandable design would run only A and C and the neutral to a single-phase 120/240 3-wire panel for all 120V and 240V single phase loads and run A, B and C to a separate three phase panel for three phase loads only and using only full rated breakers.
Thank for the quick and informative replies. My understanding was correct but I needed confirmation.
I agree that the best installation would call for a single phase sub with A, C & Neutral for the 120 & 240v loads -That way there is no chance of somebody coming along later and running a new 120v branch circuit using the high leg!
But - If we are talking about a substantial load (mostly 240v lighting) wouldn't balancing the system be an issue?
I'm thinking of installing all of the 240v loads in a 3ph panel (using ALL straight 240v breakers rather than a few slash-rated on the A to C loads)
and a small sub for the 120s because I do like the idea of keeping any neutral-connected load out of the panel.
One more thing: I had asked about the safety of slash rated breakers when misused by installing on the "B" leg. Other than setting a bad example, and that the installation would not be compliant, I'm curious as to the consequences. Or maybe a better question is, "what is the difference between slash rated and straight 240v breakers?
Maybe the insulation rating is different.
It seems to me that everything inside the breaker would be of the same spec's: The thermal and magnetic tripping properties would be exactly the same so there's really nothing left but the insulation and heat dissipation which might cost another 2 cents worth of plastic!
Nothing logical warrants the huge difference in price between a slash and straight rated breaker.
If anyone has any theory or knowledge about the actual difference in the breaker I'd be interested to hear.
Thanks again for all who replied. DX