I'm adding some new circuits. Since I have very few slots left in the panel, I'm using 'tandem' breakers (two single-pole breakers in a 1" slot). My panel is a Murray. Home Depot sells two versions of these Murray breakers: a MP1515 and an MP1515N. The only difference between the two is that the latter is labelled "nonlimited". What does "nonlimited" mean and why would I want it? The nonlimited version costs $5 more, but cost isn't the real issue. I want to make sure I'm using the right thing.

 

If the panel schedule or circuit list shows two circuits off of one slot then you could use either one if they will fit. The non limiting label is to indicate that the unit so marked is not meant to be in a CTL or circuit limiting panel. If the panel is listed on it's label as a CTL assembly then you would use only the MP1515 breaker in that panel. If the breaker will not fit than you really are out of spaces and you need to find another solution.

If the panel is not marked as a CTL assembly then only the non limiting breaker will fit in that panel. The installation of a non limiting (non CTL) breaker in a non CTL panel is only acceptable if the panel is marked as accepting that type of breaker on the label that includes the electrical testing laboratory listing mark and then it should only be installed in a slot that is shown as having two breakers on the panel's circuit diagram.
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Tom H

 

If you look at the breakers side by side, the non limiting breaker will have a "deeper" slot were the breaker clips on the the panel bus. A non limiting breaker will work on either bus, however a limiting will only work on the limited style bus.

 

Thanks for the explanations. My panel (about 7 years old) is a CTL panel. Fortunately, the slots that accept tandem breakers are at the bottom of the bus and that (not coincidentally) is where the empty slots are. So, if I understand correctly, I should be able to buy the CTL class breakers and save myself $5 per.

Thanks again.