Immersion heater supplied from a socket-outlet

A 3 kW immersion heater connected to a socket-outlet of a ring or radial final circuit may lead to an overload on the circuit.

Solution

BS 7671 does not require an immersion heater to be supplied through a dedicated circuit. There are two reasons however, why an immerision heater should be supplied from a dedicated circuit:

1. Possibility of overload
2. Compliance with Regulation 314.1

Possibility of overload

Although an immersion heater is not liable to overload there is a risk of an overload on a circuit supplying both the water heater and other items of current-using equipment supplied from the same circuit.

A 3 kW immersion heater will cause approximately 13 A of current to flow. When a tank of water is to be heated the 13 A current flow will remain for a significant period of time, during which there is a potential for overload should any other load be added to the same circuit.

Compliance with Regulation 314.1

Regulation 314.1, amongst other things, requires that every installation is divided into circuits to avoid hazards and minimise inconvenience in the event of a fault. Where an immersion heater is supplied from the same circuit as, for example, socket-outlets (thereby forming part of a ring or radial final circuit), the automatic disconnection of the circuit would lead to a loss of supply to both the socket-outlets and the immersion heater, possibly causing inconvenience.

In addition to the above requirements, Topic S225-17 of the Electrical Safety Council Technical Manual suggests that a water heater fitted to storage vessels having a capacity in excess of 15 litres should be supplied through its own circuit and connected through a 13 A fused-connection unit with cord-outlet complying with BS 1363-4 or a double-pole switch with cord-outlet complying with BS EN 60669-1 or BS EN 60669-2-4.

Where during periodic inspection, an inspector finds an immersion heater supplied from a socket-outlet on a ring or radial final circuit a Recommendation Code 2 should be recorded.

Regulation 314.1(part)

Every installation shall be dived into circuits, as necessary, to:

1. Avoid hazards and minimize inconvenience in the event of a fault