Electrical safety monitoring system utilizing a heartbeat signal indicative of voltage present on line inputs

An electrical safety monitoring system comprising:

• a housing;
• an analog circuit disposed within the housing and having line inputs for hardwiring a first line (L1), a second line (L2), a third line (L3), and a ground (GND), wherein each of the line inputs is a three-phase connection, wherein the analog circuit is configured to monitor if voltage exists between any two of the line inputs and further configured to visually indicate presence or absence of voltage on each of the line inputs;
• a heartbeat circuit electrically connected to the analog circuit to provide a heartbeat signal indicative of voltage present on any of the line inputs, the heartbeat signal encoding state information for the line inputs;
• an isolated voltage source electrically connected to the heartbeat circuit to power the heartbeat circuit with a VDC+ and a VDC−;
• a logic circuit in operative communication with the heartbeat circuit for monitoring input from the heartbeat circuit and decoding the input from the heartbeat circuit to determine state information for the line inputs;
• wherein the heartbeat signal is set to the VDC+ for a first portion of a cycle and to the VDC− for a second portion of the cycle if there is voltage detected at any of the line inputs according to a first ratio which represents a ratio of the first portion to the second portion;
• wherein the heartbeat signal is set to the VDC+ for the first portion of the cycle and to the VDC− for the second portion of the cycle if there is no voltage detected at any of the line inputs according to a second ratio which also represents a ratio of the first portion to the second portion, the second ratio different from the first ratio.