Waterproof couplings generally refer to wall penetration couplings. Wall penetration couplings are also known as wall penetration pipes, waterproof couplings, and pre-buried wall pipes. Waterproof couplings are divided into rigid waterproof couplings and flexible waterproof couplings. In electrical applications for conductivity, they are called alternating current wall penetration couplings. They can be categorized by material into dry-type capacitor-type alternating current wall penetration couplings and porcelain-insulated alternating current wall penetration couplings, respectively abbreviated as silicone rubber couplings and porcelain sleeves.