Parallel ballasts use a single wire for connections to each end of a fluorescent tube. A shunted lampholder connects the lamp pins together. Generally instant start ballasts are wired in parallel.
2 and 3 lamp parallel ballasts use blue wires for individual connections, and red wires for common connections. Black wire is for line voltage and white wire for neutral. A parallel ballast uses a single wire which connects from the ballast to each of the lamp terminals.
2 Individual wires, 1 common wire
One 2 lamp and one 1 lamp ballast
4 Individual wires, 2 common wires
4 lamp parallel ballasts and 2 lamp series ballasts use blue and red wires for individual connections, and yellow wires for common connections.
3 Individual wires, 1 common wire
Parallel Ballast Wiring