Electrical Coordination: Don’t Be Trippin’

Posted by Nick Bloom on Tuesday, January 31, 2023

nightime city illustration with one building out of power

It’s 10pm on Saturday. A notification pops on screen that your facility just experienced a power loss. Instead of finishing your movie and heading to bed, you drive over to investigate. On the way, you call the power company to report an outage, but the power company doesn’t have any indication of an outage on their system. As you get closer, all the buildings around still have power. When you get inside, you find the main breaker tripped. After further investigation, you find the breaker for one of your larger motor drives has also tripped. Once you get an after-hours electrician on-site to troubleshoot, it is determined the drive had an internal fault, but the fault tripped the main breaker as well. This motor powers a redundant pump, and the control system could have simply activated the other pump had the main breaker not tripped. Several hours later after troubleshooting, you reset the main breaker and everything comes back to life. Relieved but exhausted, you go home to bed.

This story is an example of miscoordination. Adjusting protective device settings or proactively replacing certain protective devices could have ensured only the breaker feeding the faulted pump drive tripped instead of taking the main breaker with it. How does this happen, you ask? Enter the electrical coordination study!

What is an Electrical Coordination Study?

A coordination study compares the time-current curves of the various levels of protective devices—circuit breakers, fuses, relays—in your facility, and recommends changes to ensure that faults are contained within the smallest possible zone, preserving your popcorn and movie night! These recommendations must balance coordination improvements with reducing arc flash hazards, as the two design goals are in tension. A coordination study as well as a short circuit study and equipment duty evaluation are done as part of every arc flash study. Learn more about power system studies.

Electrical Coordination Benefits

Improved protective device coordination can prevent costly outages, violation of permits, and inconvenience to those who depend on your facility’s availability. For example, a facility-wide outage due to miscoordination at a wastewater treatment plant could result in a permit violation and clean-up effort. In a manufacturing facility, it could result in the costly scrapping of all in-process product. In a hotel, you might be dealing with angry guests as well as lost revenue from on-site dining. In some cases, code requirements dictate selective coordination, particularly for emergency systems. No matter what type of facility you are responsible for, unplanned and unnecessary power outages are something you want to avoid.

The impetus is on facility managers to protect the health and safety of their employees from known hazards. At the same time, facility managers are working to ensure their facilities operate reliably to deliver vital services for those who depend on them. If you need help or have questions, reach out!

Nick Bloom, PE Photo

Nick Bloom, PE

electrical engineer

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Categories: Buildings & Campus  |  Industrial & Manufacturing  |  Municipal Infrastructure

Tagged: Electrical  |  Engineering

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