The 3 essential rules for selectivity in earth leakage protection

admin | 9 de July de 2014

A large part of unwanted tripping in an installation is caused by a lack of selectivity coordination between the earth leakage protections. With good installation practices, we can solve a large part of the earth leakage protection tripping.

Selectivity in earth leakage protection must be both horizontal and vertical. In this article, we will deal with the 3 essential rules for vertical selectivity

3 conditions must be met in order to guarantee correct vertical selectivity:

Amperometric selectivity

 Amperometric selectivity


This condition must ensure that the sensitivity value of the earth leakage protection connected upstream (I∆1) is more than double the sensitivity of the protection connected downstream (I∆2).

For example, with an earth leakage protection with a sensitivity of 30 mA (I∆2) we might have a protection of 100 mA (I∆1) or higher upstream.

Only with amperometric selectivity would we meet one of the three conditions, so the selectivity would only be partial.

 Amperometric selectivity

Chronometric selectivity

 Chronometric selectivity


This condition must guarantee that an earth leakage protection connected upstream (t1) does not act before a protection downstream (t2) to avoid any current value.

The response times must be kept below the safety limit times.

We will achieve total selectivity along with amperometric selectivity.

 Chronometric selectivity

Type selectivity

 Type selectivity


To guarantee vertical selectivity, the type of class or earth leakage protection upstream must be the same as or higher than the protection installed downstream.

Due to the ever-larger demand in earth leakage protections in installations, more and more type A and type B protections are required, which makes it necessary to respect the vertical selectivity according to the type installed downstream.

 Type selectivity

Selectivity requirements

With CIRCUTOR's RGU-2, RGU-10, RGU-10B and CBS4 earth leakage protections, we can adapt to the selectivity requirements of any installation. We can therefore easily adapt both to the necessary parameters of sensitivity and time.

Earth leakage protection

With a single earth leakage protection, we are able to protect a single load, a sub-panel or a general supply. All of this added to their ultra-immunity and high performance (prealarm, display and communications), make CIRCUTOR earth leakage protections the ideal option for any installation.


Francesc Fornieles Castells

Responsable de Mercados - División Gestión Energética y Calidad de Red
Markets Manager - Energy Management and Power Quality Division