Switch­ing

Model Rail (UK) - - Workbench -

‘Po­lar­ity’ is one of those jar­gon words that may con­fuse the elec­tri­cally unini­ti­ated. In its loos­est sense, po­lar­ity means the di­rec­tion in which the elec­tric­ity flows. Your point blades may be point­ing to one par­tic­u­lar track, which would al­low a train to take that route. But elec­tric­ity doesn’t care about which way the point blades are go­ing. If the frog is live, elec­tric­ity will flow across it and out down both di­verg­ing tracks. It doesn’t take much imag­i­na­tion to think about the chaos that this could cause. There needs to be a way to en­sure that the power flows out only along the cor­rect track. You can rely on the point blade mak­ing con­tact with the stock rail to trans­fer power through the point. But if you’ve painted and bal­lasted the track then dirt can get in there, or the point’s spring mech­a­nism can fail. To en­sure re­li­able op­er­a­tion and to get over the is­sue of po­lar­ity, you can add a phys­i­cal switch to the point’s po­lar­ity.

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