Published: 5 June 2014
Category: Q&A
James asks this question, which is about instantaneous water heaters and whether they should be wired on their own circuit, or with two or three on the same radial circuit. It has been answered by the NICEIC (Theme – Electrical Heating, Ventilation and Control):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: Should instantaneous water heaters be wired on their own circuit, or is it acceptable to wire two or three of them on the same radial circuit?
Answer: Ideally these pieces of heating equipment should be on their own circuit because of the nature of the loading and the high current that is likely to be taken. This is mentioned in the ‘On Site Guide’ to the Wiring Regulations – see Appendix H5, page177 and the BS 7671:2008 Section 554.1, page 175 'electrode water heaters and boilers'.
However, if this is an existing arrangement, then consideration must be made to the effects of overload and inconvenience on the circuit.
Regulation 314.1 mentions division of installation and the requirement for safe inspection and testing and maintenance.
All of these factors must be considered when designing the circuit arrangement.
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