Pittway Notifier AFP1010, Руководство по устранению неисправностей, Страница: 6 / 48

AM2020/AFP1010 Troubleshooting Guide 50432 Revision A 8/13/97
6
Note: The square wave is detected at
an improper amplitude so a ground
fault is indicated.
In a similar manner, a ground fault will be detected when a voltage carrying
conductor (such as: +5 or +24 VDC) is faulted to earth ground. A representation
of a positive ground fault is shown below.
Figure 2-3: Schematic representation of a positive ground fault
The Affect of Multiple Impedances to Earth Ground
It is important to realize that these paths to ground need not be dead shorts. In
the very common case shown below, multiple seemingly-minor ground faults
combine to exceed the ground fault threshold of the power supply.
The main power supply is shown with it's reference to earth ground (Point "a").
The SLC loop is shown with multiple high impedance paths to ground (Z1, Z2,
Z3, Z4, and Z5) these may result from any number of problems, such as a nick in
the insulation of an SLC loop wire, moisture or water in a backbox or conduit.
Figure 2-4: Schematic representation of a typical ground fault
condition caused by combined impedance
www.PDF-Zoo.com
firealarmresources.com