Page 267 - Electrical Safety of Low Voltage Systems

250 Chapter Fifteen

FIGURE 15.7 Connection of ECPs at the running rails.

In fault conditions, the diode is directly polarized, becomes a short
circuit, and links the ECPs to the rails.

15.5 Electrical Safety in Swimming Pools
Swimming pools may contain submersed electrical items (e.g., light
fixtures), which may break down. The underwater faulted equipment
can be modeled as a spherical electrode radially leaking current to-
ward the source both in the water and in TT systems, in the surround-
ing earth. Thus, a current field is generated and is characterized by a
current density vector J, defined as the current passing through the
unit area of the conductive medium (e.g., the water). Thus, through
the swimmer, which can be thought of as a submersed conductive
cylinder of radius k, a dangerous current I s may circulate. To calculate
this current, let us assume that the equivalent cross-sectional area of
the swimmer/cylinder S k is oriented perpendicularly to J (Fig. 15.9)
and that the swimmer is at a distance r from the faulty item.
In the above conditions, the current I s flowing through the swim-
mer is a scalar quantity given by Eq. (15.1):

I 2 Ik 2
I s = JS k = k = (15.1)
4 r 2 4r 2