Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used when more than two current carrying conductors, high currents and/or protection from environmental hazards are required. In many countries sockets are available that completely enclose a normal plug and have seals around the cable to exclude water. These reduce the need for special plugs and sockets but are often only suitable for fixed sockets due to their bulk, shape, and cable entry arrangements. Sockets on domestic extension leads are usually either not covered at all or covered with small covers that don't enclose an inserted plug. Some connectors exist that are neither industrial nor multiphase but have higher voltage or current ratings than the normal plugs and sockets. These are listed in the AC power plugs and sockets article grouped with the normal plugs and sockets of which they are variants. Almost all three-phase power plugs have an earth connection, but may not have a neutral, because large equipment tend to be delta connected. Such plugs have only four prongs.

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