Calculation of the Touch Voltage Limit

ΤΤ Earthing System, with RCD:

ΤΤ Earthing System, without RCD:

ΤN Earthing Systems:


And with:

the nominal sensitivity of the RCD

the current causing the operation of the protective device at the maximum time threshold

the external impedance

the impedance of the earthing electrode

the impedance of the phase conductor

the impedance of the protective conductor

Verification of the Touch Voltage Limit

The software, in accordance with regulation 411.5.3, verifies that the touch voltage does not surpass the allowable limit:


is the maximum touch voltage as it has been defined by the user



For TT earthing system, the software calculates this value in order to satisfy the check for touch voltage.


The value of ZA is verified that is less than 200 Ω, as recommended in the ON SITE GUIDE, Section 10.3.5.