Page 187 - Electrical Safety of Low Voltage Systems

170 Chapter Nine

FAQ

Q. What is the difference between IT systems and electrically separated sys-
tems?
A. In IT systems, the power source is not solidly connected to earth, but
enclosures of ECPs must be grounded. In electrically separated systems, the
power source is still not connected to earth, but ECPs must not be grounded.
As seen, in IT systems, the fault currents through the human body might
reach lethal magnitudes of tens of amperes in the absence of the grounding of
the ECPs.
In electrically separated systems, there is no need for earthing ECPs, as
the fault currents to ground are limited to harmless values by definition: the
product of the nominal voltage of the separated circuit (in volts) and its length
5
(in meters) must not exceed 10 V · m, and the length of the wiring system must
not exceed 500 m. These two conditions actually define electrically separated
systems and, thereby, dictate the number of transformers necessary to fulfill
them.

Endnote

1. Intheabsenceofaneutralpoint(e.g.,deltaconnectionofthesystem),anartificial
neutral can be created.