Wiring diagram for scissors crossing, The traction current feeds to the `out of the box' Peco code 55 scissors crossing must be switched to avoid shorting when vehicle wheels pass over the integral diamond crossing. This is best achieved with a 4 pole double throw switch. This applies to electrofrog (all metal) crossings only, insulfrog (insulated plastic crossing rails) do not require switching as the platic insulated crossing sections are long enough to ensure shorting does not occur..