Since rail signal circuits must be highly reliable, special techniques are used to detect and prevent failures in the relay system. To protect against false feeds, double switching relay contacts are often used on both the positive and negative side of a circuit, so that two false feeds are needed to cause a false signal. Not all relay circuits can be proved so there is reliance on construction features such as carbon to silver contacts to resist lightning induced contact welding and to provide AC immunity.
Since rail signal circuits must be highly reliable, special techniques are used to detect and prevent failures in the relay system. To protect a.gainst false feeds, double swit,ching r!elay contact,s are often used on both the positive and negative side of a circuit so that two false feeds are needed to cause a false signal Not all relay circuits can be proved so there is reliance on construction features .such as carbon to silver contacts to resist lightning induced contact weldin:g and to pr:ovide AC immunity