This British Standard applies to a single-pole or multi-pole indicator comprising a flag or shutter, operated electro-magnetically at a nominal voltage of 24 volts D.C., giving a visible signal appropriate to the state of the elec-trical circuit or circuits to which it is connected.
BS G 133:1951 history
0000 BS G 133:1951(2009)
1951BS G 133:1951 Specification for electro-magnetic indicators for extra low voltage aircraft systems