Macromatic’s three phase monitor relays are used to prevent phase or voltage errors from causing equipment shut downs. They are available with either plug-in style or DIN-Rail mount housings. The plug-in type connects to an 8-pin octal socket while the DIN-Rail mount type features units with slim, space-saving housings or with Modbus TCP communication capability. A few models also have universal voltage (190-500V). The difference between single phase and three phase is that single phase has two wires for phase and neutral, while three phase has three wires for three currents besides the neutral wire. Because of this, three phase systems can handle the larger loads found in industrial applications. Some examples of common uses include pumps & motors, elevators, and process equipment.

The types of errors detected by these phase monitor relays, also called phase protection or phase control relays, include phase loss, phase reversal, phase unbalance, undervoltage and overvoltage. Phase loss occurs when at least one of the three phases goes down. This can cause damage to equipment if undetected and can be caused by blown fuses or broken wires. When a phase reversal happens it causes a motor to run in the other direction, becoming a danger to itself as well as anyone who may come in contact with it. Unbalanced phases are caused when the load is not evenly carried between the 3 phases, which might create overheating. Under or overvoltage errors happen when the voltage in all three phases rises or drops at the same time. Many of these relays are also designed to still show a fault even if a phase is lost.

A few units only check for one type of phase error, but most will check for multiple types of errors. All of the phase monitor relays check for phase reversal. The PCP series is the only one that checks for one type of error. The PLP series monitors phase reversal and phase loss while the PAP and PBDU series also check for undervoltage conditions. All of the other series can monitor for or indicate for all five types of phase and voltage errors. The relays that check for voltage errors feature true RMS measurement for more accurate sensing.

All of the Macromatic three phase monitor relays carry a cULus listing. For the plug-in models, they have that approval only once they are plugged in to the corresponding socket. Except for the PC Modbus communication relay, all of them also carry CE approval. Sockets and other accessories such as hold down springs are sold separately.