A system for measuring wiring impedance in an emergency notification circuit, the system comprising: an end-of-line capacitor; a plurality of notification devices (14a- 14n) connected in parallel with the capacitor; a first reference resistor; a second reference resistor through which the capacitor may discharge; and a controller configured to open first and second switches (20a-20b) arranged between a voltage source and the controller and to charge the capacitor by current from the voltage source, through a resistor, through the wiring impedance, through the capacitor, through a further resistor and through the first reference resistor; to determine, during charge-up of the capacitor, the capacitance of capacitor by monitoring the voltage across the first reference resistor, by determining the time constant of the capacitor, the resistor, the further resistor, the first reference resistor, and the wiring impedance, with the resistors (24a-24c) being known, and the value of the wiring impedance being small compared to that of the resistors (24a-24c); to determine an RC time constant of a discharge circuit including a system diode, the capacitor, the wiring impedance, and the second reference resistor based upon the monitored voltage across the second reference resistor during discharge of the capacitor, with the second switch being closed and the first switch remaining open, in order to discharge the capacitor, where R is a sum of resistance of the second reference resistor and the wiring impedance, and C is capacitance of the capacitor; and to determine the wiring impedance of the emergency notification circuit in response to the RC time constant, with values for the system diode, the capacitor, and the second reference resistor being known. an end-of-line capacitor; a plurality of notification devices (14a- 14n) connected in parallel with the capacitor; a first reference resistor; a second reference resistor through which the capacitor may discharge; and a controller configured to open first and second switches (20a-20b) arranged between a voltage source and the controller and to charge the capacitor by current from the voltage source, through a resistor, through the wiring impedance, through the capacitor, through a further resistor and through the first reference resistor; to determine, during charge-up of the capacitor, the capacitance of capacitor by monitoring the voltage across the first reference resistor, by determining the time constant of the capacitor, the resistor, the further resistor, the first reference resistor, and the wiring impedance, with the resistors (24a-24c) being known, and the value of the wiring impedance being small compared to that of the resistors (24a-24c); to determine an RC time constant of a discharge circuit including a system diode, the capacitor, the wiring impedance, and the second reference resistor based upon the monitored voltage across the second reference resistor during discharge of the capacitor, with the second switch being closed and the first switch remaining open, in order to discharge the capacitor, where R is a sum of resistance of the second reference resistor and the wiring impedance, and C is capacitance of the capacitor; and to determine the wiring impedance of the emergency notification circuit in response to the RC time constant, with values for the system diode, the capacitor, and the second reference resistor being known. to open first and second switches (20a-20b) arranged between a voltage source and the controller and to charge the capacitor by current from the voltage source, through a resistor, through the wiring impedance, through the capacitor, through a further resistor and through the first reference resistor; to determine, during charge-up of the capacitor, the capacitance of capacitor by monitoring the voltage across the first reference resistor, by determining the time constant of the capacitor, the resistor, the further resistor, the first reference resistor, and the wiring impedance, with the resistors (24a-24c) being known, and the value of the wiring impedance being small compared to that of the resistors (24a-24c); to determine an RC time constant of a discharge circuit including a system diode, the capacitor, the wiring impedance, and the second reference resistor based upon the monitored voltage across the second reference resistor during discharge of the capacitor, with the second switch being closed and the first switch remaining open, in order to discharge the capacitor, where R is a sum of resistance of the second reference resistor and the wiring impedance, and C is capacitance of the capacitor; and to determine the wiring impedance of the emergency notification circuit in response to the RC time constant, with values for the system diode, the capacitor, and the second reference resistor being known.