No! Certainly not 'commercial', don't know where you would get that idea from?

You have a main switchboard, then you have secondary ones, and (usually) finally 'tertiary' ones — though we wouldn't usually call them that in EN.

Depending on the exact set-up, the main and secondary ones might or might not be LV; but the tertiary one almost always will be.

There are plenty of other ways they might be described, depending on the configuration of the specific installation; but this would be a general-purpose solution that could hardly be wrong in any situation, even though there could be better solutions in certain instances.

Do note that in this context, 'low voltage (almost invariably abbreviated as 'LV') normally means 'conventional mains voltage' (220 V, etc.)


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Note added at 4 jours (2016-07-20 08:40:17 GMT) Post-grading
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'panel' is another possibility advocated by at least two peer commenters below; my personal preference is to reserve that for translating 'tableau', but it is certainly technically plausible — as so often, there is a choice of possible terms, and only knowledge of the actual form it takes makes it possible to unequivocally choose between them.

On a ship, I'd be inclined to think that this is indeed likely to be some kind of 'panel' located in a 'cupboard' — those have been very common on the ships I've worked on, but obviously other possibilities exist.