Issue
How many devices can be connected to between D333A (Ground Fault Isolator)?
Solution
Style 7 Configuration
According to NFPA 72, a Class A style 7 circuit must be able to detect alarms with a wire to wire short (any single short on the wiring shall not prevent any device from operation). A true Class A style 7 Circuit would require a D333A Circuit Fault Isolator on either side of each device on the polling circuit. A maximum of 127 D333A modules can be connected to a polling circuit, thus allowing a maximum of 63 other devices to the polling circuit.
Modified Style 7 Configuration
For a modified style 7 wiring, the D333A Short Circuit Isolator should be located between any devices on the analog communication loop. In the event of a short on the loop, two adjacent D333A Isolators (closest isolators to the left and right of the shorted section) activate and their respective LED indicator turns on. This prevents entire loop failure. Upon removal of the short condition, the D333A automatically restores the entire loop to the normal operating state.
Modified Style 4
Do not connect more than 25 devices between any two D333A Short Circuit Isolators where the total line impedance between these two isolators is greater than 12 Ohm, or length between two isolators is more than 4000ft. using #14AWG wire or 2000ft. using #16AWG.
Part numbers D10024A, D10024, D9024, D8024, D333A
