Choosing the relay type will depend on your application requirements, such as speed of switching, lifespan of the relay, and maximum voltage to switch. Solid state relays are chosen for their long life as well as their fast actuation time. Solid state relays can have actuation times as fast as 100microseconds, making them perfect for applications that require high-speed switching. Their primary drawback is their off-state leakage current, which can leave a device continually turned on in a high impedance digital circuit, or can cause significant errors in analog circuits. Mechanical relays are chosen for their versatility. Normally-open and normally-closed contacts, as well as multi-pole configurations and dry circuit contacts, are available. Mechanical relays have no off-state leakage current. Their drawbacks are slower switching times, shorter life span, and, in some instances, electrical noise in both the coil and contact circuits.