Polarity
Polarity turns up in 2 fields: electrotechnology, fiber optics. Here is what it means to the people in each one.
Polarity in electrotechnology
The direction of an electric field or the designation of positive and negative terminals.
Polarity indicates the relative electrical potential of terminals in a circuit, defining which is positive and which is negative. In direct current systems, polarity is fixed and dictates the direction of current flow. In alternating current systems or transformers, polarity refers to the relative instantaneous phase relationship between primary and secondary windings, which is critical when paralleling equipment.
"Before you parallel those two distribution transformers, you must verify their phase polarity or you'll create a dead short."
Polarity in fiber optics
The arrangement that ensures each transmitter in a fiber link connects to the receiver at the far end.
A duplex link needs the transmit fiber at one end to arrive at the receive port at the other, so somewhere along the path the pair must cross over. In duplex cabling this is called A-to-B polarity. For MPO trunks and cassettes, cabling standards define methods A, B and C that combine trunk type, adapter key orientation and jumper type to keep every lane straight.
"Both ends show light out but nothing in, polarity's backwards, roll one of the jumpers at the switch."