Re: Operator safety Motor Control Center solutions review

Home Electrical Engineering Forum General Discussion Operator safety Motor Control Center solutions review Re: Operator safety Motor Control Center solutions review


Thank you for your interest, Laurent. Our Plant is a Class 4 Wastewater/Sewage Treatment Plant, with two 27.6 kV incoming lines, and 4160 volt distribution across the plant, to 600 volt MCC’s, etc. After a Plant-wide electrical assessment was done two years ago, and an Arc Flash Study completed, we found that some of our arc flash levels were too high for any PPE to protect. So, we talked to Electroswitch, who were beginning to manufacture Close/Trip switches with built-in electronic time delay relays. They feature the usual pistol grip for immediate closing or tripping, with the addition of time-delayed closing and tripping by means of color-coded push buttons, with LED’s that flash as the timer is timing. During the last few seconds of timing, the LED will flash at twice the frequency, as an added warning that closing or tripping is about to occur. These switches also have the feature of allowing you to ‘cancel’ the timing sequence by pressing the other push button. For example, if you are timing out a Closing operation, you can cancel it during the timing by pressing the Trip button. We have a system of Main-Tie-Main breakers on our substation breakers and on our 600 volt switchgear mains, and these are the breakers that we are installing the time-delay switches on, wherever there were existing Close/Trip switches. (So we did not put them on MCC’s, for example). What this does for us is 1) It gives us immediate protection for personnel doing the switching, and 2) It buys us time to have the proper engineering done to mitigate the arc flash hazard levels.