Why do we have to connect our fire panel and addressable circuits to earth?
We use the A/C mains earth from the DB board as it provides a low-impedance path to the earth to prevent hazardous voltages (high voltage spikes) from appearing on our fire panels. It keeps people safe by preventing electric shocks and helps prevent damage to our panels and devices by preventing excessive current from running through the mains circuit.
Earthing provides a low resistive conductive path directly to the earth, which carries any such fault or leakage current away from the electronics.
Earthing of our addressable detection loops is equally important as it limits the build-up of static electricity, prevents induction of noise from other circuits in close proximity and prevents stray potentials entering our detection data route by grounding these sources.
The earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level.
In electronic circuit theory, a "ground" is usually idealized as a sink for charge, which can absorb an unlimited amount of current without changing its potential.
Ground loops are a major cause of noise, hum, and interference in electronic systems therefore we do not connect both ends of our screen conductor to earth. We connect one end of the loop only (called a floating earth).
The screen conductor of the PH30 cable must be connected to earth in the panel and be contiuous throughout the entire circuit (there is a termination point on all detectors) and when returning to the fire panel the screen must be cut off.
Note: Some newer panels provide a software switch that must be programmed for the “ON” condition to ensure earth protection.
A properly earthed system provides for a safe system against electrical shock and prevents interference producing spurious conditions occurring on your panel display.