Glossary
SELV, safety extra-low voltage (muy baja tensión de seguridad, MBTS)
A supply system at very low voltage, up to 50 V AC, taken from a safety source and isolated from earth. It is used in pools, baths, fountains and door entry systems because touching it carries no risk of electrocution.
What SELV is
Safety extra-low voltage, known in Spain as muy baja tensión de seguridad or MBTS, is a way of powering equipment at a voltage so low that touching it is not dangerous: up to 50 V AC, compared with the 230 V of a normal socket. It is covered by ITC-BT-36 of the REBT.
How it is obtained
Lowering the voltage is not enough: the source must be a safety source, usually an isolating transformer or equivalent, that fully separates the extra-low voltage circuit from the 230 V one. The SELV circuit is also kept apart from earth and from other circuits, so a fault on the mains can never reach the protected side.
Where it is required
- Swimming pools: in zone 0, the pool basin itself, underwater lights must run on SELV at 12 V AC, with the transformer outside the pool zones, under ITC-BT-31.
- Bathrooms: in zone 0 of baths and showers only 12 V SELV equipment is allowed, with the source outside the bathroom zones, under ITC-BT-27.
- Ornamental fountains and ponds.
- Door entry systems and doorbells, which work at extra-low voltage.
What to check in your pool or bathroom
- That the pool lights are 12 V and have an IP rating suitable for immersion.
- That the transformer is in a dry, ventilated place away from the water.
- That nobody has swapped in 230 V lights to gain brightness.
In a pool, safety is completed with an RCD, equipotential bonding and a sealed board. See swimming pool electrics in Seville, Spain.
Related services
Swimming pool electrics
We carry out swimming pool electrical installation in Seville, Spain and the Aljarafe under ITC-BT-31: a filtration pump control panel with timer and protection devices, pump connection, 12 V LED lights, weatherproof sockets and equipotential bonding, with the installation legalised. We also repair the pump that will not start and the RCD that trips when the filtration switches on.
Bathroom electrics
We install bathroom electrics in Seville, Spain following the protection zones of ITC-BT-27: earthed sockets where they are allowed, extractor fan, electric towel rail, illuminated mirror and equipotential bonding. For renovations and for bathrooms that give you small shocks or trip the power today.
Door entry systems and doorbells
We carry out door entry system repair in Seville, Spain: intercom handsets that do not ring or will not open the door, entrance panels with broken buttons, door releases that do nothing and silent doorbells, in flats and apartment buildings. We replace the handset with a compatible one, renew the panel at the street door and install access control with cards or your phone.
Need an electrician in Seville, Spain?
Call us or send a WhatsApp message with a photo of the job. You get a fixed quote before any work starts.