Three-Phase Monitor Relays
Calculating the Short Circuit Current Rating for control panels requires establishing the SCCR for each of the individual, relevant power circuit components. What about the Phase Monitor Relay used to measure the circuit voltage?
Macromatic devices work on many systems. Here are the guidelines and recommended connections for Open Delta, Corner Grounded and High Leg (Red Leg, Wild Leg) Delta systems. Contact Macromatic for technical information on other systems.
Issue: Schneider Electric (Square D) has obsoleted their complete line of 8430 MPS plug-in & MPD surface-mount phase monitor relays. I see Macromatic has several products I could use to replace the Square D products. Are there any special issues to address? Solution/Resolution: The following are the steps required to replace an obsolete Square D product with one from Macromatic
Issue: I have an application where the panel control voltage is at 120V AC, but I need to have a 24V DC alarm circuit if the three-phase monitor relay trips. How can I do it without adding a relay to the circuit?
Issue: Are fuses required and what size fuse do you recommend using with your Phase Monitor Relays? Solution/Resolution: The use of fusing in-line with Macromatic phase monitor relays is not required; however, Macromatic recommends using a 2 ampere, fast acting, voltage appropriate fuses such as a KTK fuse between the Phase Monitor Relay and the three phases (see diagram below). Use of fusing in-line with loads controlled by the relay output should also be considered depending on the application. Marked safety and regulatory approvals, including UL Certifications, do not require the use of inline fuses in typical applications. Please be aware that different guidelines may apply in your specific application and/or installation.
Issue: Can Macromatic's 3 phase monitor relays be used with open delta systems?
Answer: Yes, by following a few simple guidelines.
Issue: Can I use a phase monitor for protection on a high-leg delta system? Answer: Yes, Macromatic phase monitor relays provide the same reliable protection on high-leg delta systems. A high-leg delta system (also commonly called red leg and wild leg among others) is a common configuration involving a transformer secondary having one winding center tapped
Issue: I have never connected a three-phase monitor relay. Do you have a typical wiring connection? Solution/Resolution: While each individual application may have its own requirements, this diagram showing a three-phase monitor relay and motor starter is fairly typical of most installations. When the three-phase voltage is present and all conditions are normal, the N.O.
In May 2015, Macromatic introduced the next generation of PMD Series Three-Phase Monitor Relays. Many important features were added to the new products. These improvements along with a comparison to the previous design are summarized.