In article ,
Phil Allison writes:

There are two major issues with large mains rated toggles when used with less other than mains voltages.

1. The contact material ( often plain brass) tarnishes with a non conductive layer. Regular use at mains voltage usually prevents this layer building up.

2. Grease applied to the moving parts of the switch migrates to the contacts, hardens and stops conduction.

In case 2, a squirt of WD40 often restores good operation, far as being a mains switch is concerned.

There's a third issue specifically with switches used on DC circuitry,
which is that current flow is constant and unidirectional and so the
arcing that occurs as a contact is made and broken will always be in
the same direction and will not be broken by the alternation of the
current, only by the contact gap getting large enough.

--
Mike Fleming