Calculation scope
Use the arithmetic tools only within the model and units stated on each page. Results depend on your input values and are rounded for display. Example values are illustrative. These tools do not establish installation safety, equipment suitability or compliance with BS 7671.
Reference material
The guides introduce the information a design or testing assessment needs. They do not replace the applicable standards, manufacturer instructions or the assessment of the person responsible for the work. The site makes no claim of professional electrical certification or independent sign-off.
Directory records
Business details can change. A listing does not establish present trading status, authorised distributor status or product availability. Confirm the relevant details directly with the supplier.
Errors and changes
If you suspect an error, stop using that result and send an issue report. Page updated 4 September 2026.