32V:
Here in the US, residential electric hot water heaters are hard-wired using a 30 amp, 240 volt circuit. There is no plug/cord connection required. It's just two wires (one from each end of the transformer to derive 240 volts) and a ground (or earth) wire. In some juridictions, a disconnect switch might be required within sight of the water heater. Commercial installations can vary greatly, but are usually three-phase services.
Electric furnaces may require multiple circuits or simply use just one large circuit. These too are wired directly, though there may be a requirement for a disconnect switch to be located within sight if the circuit breaker(s) feeding the unit are not within sight. We do have some exceptions where padlock attachments for these breakers are considered an alternative to a separate disconnect at the furnace. In my home, the furnace is fed by a single 80 amp, 240 volt breaker with a padlock attachment in the main panel.
Outdoor air condintioning compressor units or heat pumps always require a disconnect switch within sight, but like water heaters, usually only require a 2-wire 240 volt circuit that is hard-wired. These can range from 20 to 60 amp loads, depending upon the size of the units.
Electric stoves that incorporate the cook top and oven in one appliance, (referred to as ranges in the US) utilize a NEMA 14-50 receptacle, or "socket".
When a separate electric cook top and oven are installed, they are generally hard-wired with no plug/socket connection. Some local codes may require these installations to be done differently.
Electric clothes dryers, the current requirement is for a NEMA 14-30 receptacle (socket) and matching cord. Dryers are always required to be plug (socket) and cord connected since they are portable appliances.
There was a time when the "earth" or "ground" wire and the "neutral" were permitted to use the same wire, resulting in just a three-wire connection for these appliances. This lasted for at least 50 years and I really don't know why it was deemed to be dangerous all of a sudden.
Electric ranges and dryers have certain components, like clocks, lights and motors that operate on 120 volts. For this reason, the new standards require that an insulated neutral wire be provided to these appliances.
Sharing the ground (earth) and neutral for minor 120 volt requirements is no longer permitted.
