each MWBC should be handle tied or on a single handle double pole breaker. this may not have been teh requirement when the work was done, but is a good idea to go ahead and do any way. all you have to do is insert a piece of ground wire thru the holes in each handle to tie them together. this keeps you from accidently getting shocked if you think the circuit is dead.

do not move any MWCB breakers unless you move BOTH and make sure that they land on opposite phases in teh new location.

If you measure 240 volts between the red and black of each cable you are OK.
In some panels it is possible to put breakers in slots beside each other and not be on opposite legs.

Thanks for the quick replies. So I need to check for voltage at 240 between the two hots. It's a 100 amp Seimens Main Panel, would anyone know if this is a panel where you can have breakers directly above eachother on seperate legs?

I'm a little confused about different legs. Does it mean that some slots in the panel get their hot from one of the incoming legs or feeds, and the other slots get it from the other incoming hot feed?

I'm assuming this only applies to multiwire circuits, meaning a regular 50 amp range breaker also has two hot legs but that double pole breaker can be located anywhere in the panel? Is this correct?

Thanks for your patience and answers
Ryan

Every breaker position is fed with one hot leg or the other. Typically they alternate so you can put a 240 breaker in so it straddles the opposing legs. However, you have to inspect the panel (or just measure the voltage as recommended) to be sure.

A 240V circuit needs both legs opened at the same time.
Under the 2008 (I believe) and earlier NEC, it's not a strict requirement that the multiwire circuit breakers open both legs when one side blows (handle tie or two-pole breaker), but it's not a bad idea. The strict requirement is only when both legs feed the same yoke (split top and bottom receptacle, for instance).

Under the 2008 (I believe) and earlier NEC, it's not a strict requirement that the multiwire circuit breakers open both legs when one side blows (handle tie or two-pole breaker), but it's not a bad idea. The strict requirement is only when both legs feed the same yoke...

I believe that if you check 210.4(B) in the 2008 NEC, you'll find that they eliminated the "same yoke" language and now require simultaneous disconnects for both legs (all legs, actually) of all MWBCs.

Thanks a lot for all the replies. I did some research on The Murray homepage and it seems like their panels have staggered legs, which would make my install correct, but I will double check visually and with a tester just to be sure.

Just out of curiosity, a true dedicated 240 double pole circuit could never have the problems of a miswired MWBC since it can only pull the amperage of the single device and the breaker will keep the neutral from overheating. Yet on a miswired MWBC you could essentially be using many devices together which could cook the neutral. Is my thinking correct? This stuff is very interesting and after doing research I was just wondering if I got it right.

Thanks again everyone
Ryan

a true dedicated 240 double pole circuit could never have the problems of a miswired MWBC since it can only pull the amperage of the single device and the breaker will keep the neutral from overheating.
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That is incorrect. A true 240v circuit only uses two hots, no neutral at all. The opposite phases cancel each other out. A 120/240v circuit requires a neutral for the 120v part but not for the 240v. The correct double pole breaker for the panel will land on both legs to produce 240v.

You are right on the part about overloading the neutral if a 120/240 circuit were to be attempted with breakers in the wrong slots. In that case you would measure 0 volts between the tow hots. A correct double-pole breaker for the model of panel will assure that the problem does not occur.

Thank you guys!