Electric Water Heaters continue…

Off-peak Operation

Where the white meter tariff is in operation it can be an advantage to heat the full contents of a tank overnight when the cheaper rate for electricity is in force and switch on the short element wizen additional hot water is needed.

This normally requires two circuits for the immersion heater installation. One circuit is used for the night rate supply, when time controlled in conjunction with night storage heaters, this supplying the long element of a dual immersion heater or the lower immersion heater of a two- immersion heater arrangement. The other circuit is from the unrestricted supply and, as it will be only for intermittent use, the circuit can be a spur of a ring circuit. For two immersion heaters, each is controlled separately but for a dual immersion heater a twin double-pole isolating switch is needed.

Automatic Control

An immersion heater can be switchea on and off automatically by means of a time- switch. A timeswitch (e.g. the ‘I merset’) has been designed especially for this purpose and gives a choice of two switch-on and switch-off periods each 24 hours. These can be programmed to suit the family’s requirements but a common arrangement is to switch off the heater late at night, on early in the morning, off after breakfast as the family leaves for work, and on again just before the first member of the family returns home. Other manufacturers also have available similar timeswitches which are equally suitable. The purpose of the timeswitch is to save electricity by not keeping a tank of water hot when none is being drawn off.

Some timeswitches have an over-ride switch to enable current to be provided to the immersion heater out of programmed hours, such as over weekends. If the time- switch has no over-ride switch a 20 A double-pole switch can be fitted and connected to the timeswitch to bridge the open switch contacts of the timeswitch to obtain hot water out of hours.

The live pole of the double-pole switch bridges the single-pole contacts of the timeswitch and also supplies current to the neon indicator. The neutral pole merely supplies the neon indicator which needs both live and neutral poles to energise the neon.

The use of a timeswitch to cut off the current to an immersion heater overnight, and at other times, does not eliminate the need for lagging the tank. The lagging, which should be at least 100 mm (4 in) thick, reduces heat losses and conserves the hot water whether the heater is ‘On’ or ‘Off’.

Instantaneous Water Heaters

Washbasins

Instantaneous water heaters having loadings of 3 kW fitted over the washbasin for hand washing can be supplied from a ring circuit spur. The connection at the water heater should be either a 13 A fused plug and socket-outlet or, as in a bathroom, a switched fused connection unit with the switch out of reach of a person using the bath.

Shower units

Instantaneous water heaters used as shower units have electrical loadings of 5 kW and 6 kW. These need separate 30 A circuits from 30 A fuseways in consumer units, the circuits being wired in 4 mm² 2-core and earth PVC sheathed cable. An isolating switch is needed with these water heater units and should be fixed within reach of the heater unit.

Where the shower unit is installed in the bathroom, there is usually difficulty in siting the switch out of reach of the fixed bath and out of reach of the person using the shower. To meet this situation a 30 A double-pole cord-operated switch has been introduced. The circuit cable, therefore, runs from the fuseway in the consumer unit to the ceiling switch and from this to the water heater unit.

Sink water heaters

For the sink, a 5 kW version of the shower instantaneous water heater is available. The circuit is the same as for a shower unit but need be only of 20 A current rating using 2.5 mm² cable and a 20 A double- pole switch fitted near the water heater.

One version of this heater, having a loading of 7 kW can be used to supply two outlets — the shower and the sink or the shower and a washbasin — a special 2-way faucet tap being fitted for the purpose, since each outlet must be of the open type.

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