This week’s question is a bit long and detailed but very important. I had quite an intense conversation with a good friend over the weekend and we began discussing some of the changes to the 2017 NEC regarding 240.87 Arc Energy Reduction. (yes, perhaps I need a hobby)

240.87 requires that if the highest continuous current trip setting for which the actual overcurrent device installed in circuit breaker is rated or can be adjusted 1200 A or higher 240.87 (A) and (B) shall apply.

240.87 (A) Documentation requires that: Documentation shall be available to those authorized to design, install, operate or inspect the installation as to the location of the circuit breaker(s).

240.87 (B) Method to Reduce Clearing Time. A list of methods is provided for reducing the overcurrent device’s clearing time (to reduce the incident energy from an arc flash). The 2017 Edition of the National Electrical Code (NEC) now includes the use of the instantaneous trip/override of a circuit breaker. This was not included in the 2014 Edition. New items on this list include:

• An instantaneous trip setting less than the available arcing current
• Instantaneous override that is less than the available arcing current
• Approved equivalent means

There are also new informational notes. Informational Note (2) discusses that if the arcing current is above the instantaneous trip, the device trips with no intentional delay. Of course, this also means that if there is not sufficient arcing current, the device would not trip instantaneously resulting in a longer clearing time - increasing the incident energy from an arc flash. Another new Informational Note (3) references IEEE 1584 as an available method for calculating the arcing current.

The focus of the new additions is to verify that there would be sufficient arcing short circuit current so the instantaneous would trip. (subject to good condition of maintenance, arcing current calculation accuracy etc. and all of those legal disclaimers)

So, with all of that, here is what this week’s question is about.

Who enforces the documentation requirement regarding the instantaneous and arcing current?

• AHJ – want to see calculations/documentation
• AHJ - just wants to know it was done
• No One - AHJ never asks
• N/A No new installations
• Many locations - Depends on Jurisdiction **

** If you selected - Many Locations, do/did any jurisdictions require documentation?

Of course, AHJ is the Authority Having Jurisdiction and could be a government official (city, county, state etc.)

This is not an easy question to provide multiple choice answers – there are many issues here so feel free to clarify your thoughts and tell us what you think!