High-immunity RCD (diferencial superinmunizado, super-immunised RCD)

What a high-immunity RCD is

It is an RCD with the same 30 mA sensitivity required in Spanish homes, but with filtering electronics that make it far more resistant to disturbances. Manufacturers mark it with letters such as SI or HPI, and Spanish electricians call it superinmunizado (super-immunised). It is usually type A, which means it also detects pulsating DC leaks.

Why an ordinary RCD trips for no reason

Many modern appliances have electronic power supplies that create tiny leakage currents and distort the waveform (harmonics). Added together, or combined with network spikes during a storm, they can trip a standard RCD with no real fault. It is typical in homes with:

• Lots of LED lighting or dimmers.
• Computers, TVs and network equipment left on all the time.
• Inverter air conditioning, an induction hob or an aerothermal heat pump.

When to fit one

If your RCD trips at night or on stormy days and no real leak turns up, a high-immunity RCD usually ends the problem. A genuine earth leak must be ruled out first, because swapping the device does not fix a damaged cable. Installations with a lot of electronics may also use type F or type B RCDs, depending on the equipment. The difference from a standard type A is immunity, not the kind of leak it detects.

Rough price

Replacing a standard RCD with a high-immunity one costs, as a guide, 90 to 250 euros fitted, plus VAT, depending on the brand and the number of poles. See high-immunity RCD and RCD keeps tripping in Seville, Spain.