MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
(OP)
Hello,
I am working on the panel schedule, and I noticed that some panel has MLO, and some panel has MCB.
I believe that the omission of a main breaker in many of these cases is due to cost and perhaps in some cases available panel real estate. Is there any rule for MLO or MCB?
I am not quite sure the reason why.
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
Sub panels often don't have a main breaker.
Actually, adding a main breaker is often due to cost.
If the code requires a disconnecting means or overload/over current protection, a main breaker is often cheaper that a stand-alone
disconnect/protection.
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Ohm's law
Not just a good idea;
It's the LAW!
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
Or as said above, sub panels would not have a main.
Actually, if you really looked at the curves, you may not want a main, but opt for a fuse as a main.
Also, if you use a stepdown transformer within the building, such as a 480 to 240, you may have a breaker on the high side, and you may not want a main on the low side.
In most homes the builder will install a panel with a main, as this cost's less than having that in a separate box.
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
While the transformer may not required an OCPD on the secondary side, the secondary conductors will almost always need an OCPD per 240.21(C).
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
So, if this 225 panelboard is fed from a 225A breaker in that distribution board (that might be only a few feet away, why would I put in a 225A main breaker instead of going with a 225A MLO panel? If there’s ever a fault that needs to be cleared by tripping at the 225A level isn’t one breaker enough? If there’s two in series and the fault is after the second one they’ll both trip anyway, isn’t one enough?
I’ll see your silver lining and raise you two black clouds. - Protection Operations
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
I have something like that on my well pump. A breaker in the panel, and a box with a breaker near the pump house (underground vault).
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: MLO(Main Lug Only) vs MCB(Main Circuit Breaker)
I’ll see your silver lining and raise you two black clouds. - Protection Operations