The difference between wet and dry contacts is how and when the contact gets electricity flowing through it. This terminology – and the distinction between them – is a common cause of confusion, even for the experts.
Dry contacts are a volt-free contact that does not supply power from a shared source to the control. You must supply your own power since these contacts are bare, with no energy.
A wet contact uses a relay device, and when it is activated, it will supply a voltage to the device that is connected to the relay. Wet contacts have one pole that is hot (or “wet”) all the time.
You should use either wet or dry contacts for certain devices. Should you use the wrong contact, the device may not work properly or up to its full potential.