installing cabling at extra low voltage for signalling, cabling or communication purposes (for example, telephone cabling, cabling for fire alarm or burglar alarm systems, or heating control systems)
Gosod ceblau foltedd eithriadol o isel at ddibenion anfon signalau neu gyfathrebu (er enghraifft, ceblau ffôn, ceblau ar gyfer system larwm tân neu larwm lladron neu system rheoli gwres).