The 2011 NEC has added more language regarding arc flash and electrical safety. Many of us are aware that using circuit breakers without an instantaneous can provide perfect selective coordination with downstream devices however when it comes to arc flash, the additional time delay can be very dangerous. Without and instantaneous the device can time delay up to 30 cycles based on its short time delay. Assuming a typical power breaker has a 5 cycle instantaneous, going to 30 cycles means there would be 6 times the incident energy.

The 2011 Edition of the NEC now contains the language:

240.87 Noninstantaneous Trip Where a circuit breaker is used without an instantaneous trip, documentation shall be available to those authorized to design, install, operate or inspect the installations as to the location of the circuit breaker(s)

Where a circuit breaker is utilized without an instantaneous trip, one of the following or approved equivalent means shall be provided:
(1) Zone-selective interlocking
(2) Differential Relaying
(3) Energy-reducing maintenance switching with local status indicator.

Jim,
Thank you for the heads up!! I have my new book but haven't opened it yet....

So what is this article requiring? Adding one of those 3 options to every breaker that does not have INST?

It's looking that way. I have used this design alot over the years with data centers, federal installations etc. Very reliable and you don't want to give up reliability.

These methods allow continued coordination under normal conditions but require some form of "Plan B" in case there is live work/arc flash hazard and the non-instantaneous breaker is the only protection to limit the arc flash.

Rather than relying on the study results to make recommendations, the NEC just made solutions an automatic requirement for new design.

Interesting, arc flash reduction switches seem to be the obvious choice, ZSI is expensive and complex.

One OEM (I have been sworn to secrecy) is launching a line of MCCB's with built in arc flash maintenence switches this year. I bet someone from that company had input here.

So this is for new installations only right? Not existing?

Glad you said it, I was only thinking it.

I assume it is for new installations since the code is not retro-active.

I just stumbled on the requirement when reading the January edition of Electrical Contractor magazine, in an article by Jim.
It looks like a good intention, but it puts that much more emphasis on doing a good job on a Power Study - Fault, Coordination and Arc-Flash analysis to assure that the Instantaneous setting isn't too high to detect an arcing fault.
And with arcing faults being 40% of the magnitude of a bolted fault on 480 volt systems, there may not be an instantaneous setting that allows typical load inrush, but still trips for arcing faults.
Nonetheless, it's good to see the NEC putting emphasis on it.
John M

We are doing a coordination and arc hazard study at a facility that was built and protection set before the 2011 NEC requirements. In your opinion, does the new 240.87 apply to our study? Do we have to either forego selectivity and use instantaneous on all breakers or recommend ZSI, differential, or maintenance switches? What if we can maintain IE within the limits of normal plant PPE (8 cal) without instantaneous trip?

The primary side of this protector will be protected by an instantaneous trip.
But the 480 customer side will only be protected by a fuse link on a time curve that is very high amperage. We work all of this energized. Or did. As a utility, we had previoulsly been exempt from NFPA. The proposed regulation changes are going to be a burden for our customers.

hurricane harry:

What proposed regulation changes are you referring to?

Thanks,
Alan

In my opinion, you don't need to comply with NEC 2011 for a couple reasons:
1) The jurisdiction you're in has most likely not accepted the 2011 edition yet, &
2) Even if they were using the 2011 edition, it's not a retroactive requirement.

But the engineering Code of Ethics (for DE) states THE ENGINEER SHALL HOLD PARAMOUNT SAFEGUARDING LIFE, HEALTH AND PROSPERITY AND PROMOTING THE PUBLIC WELFARE IN THE PERFORMANCE OF HIS PROFESSIONAL DUTIES.

... hmmmm!

Personally, if I could get the incident energy to a level of 8 calories, I'd be comfortable with that.

John M

It is my understanding that utilities are not required to comply with NFPA 70e at this time. OSHA will adopt these inside wireman regulations soon, rather than do an independant analysis of utility needs.

SquareD white Paper

SquareD white Paper is attached.

Thanks for the link. It's interesting that Square-D considers that having an instantaneous function available, even if it is set to OFF would mean you don't have to meet the new instantaneous requirement.

But Eaton, in their article on the subject http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=347878 says it would.

The Square-D interpretation only makes sense if you allow changing the instantaneous setting from OFF to some value for maintenance, instead of using a maintenance switch.

Do clarifications of comments on proposed NEC changes have any authority? Can anyone find a link to the CMP 10 comment referenced?

I think you are correct. Thanks. Unless we recommend installing new protective equipment, 2011 would not apply. Also, this is in Virginia which still uses NEC-2008.

I believe that all UL489 breakers must always include some amount of instantaneous tripping even when the INST function is dialed Off. UL489 devices are not rated for 30 cycle withstand, like ANSI C37/UL 1066 devices are.

IAEI Article



An article in the March/April edition of the International Association of Electrical Inspector's magazine also references the CMP-10 statement on comment 10-41. The articles says the new requirement pertains to the absence of an instantaneous trip function, not the absence of an instantaneous trip setting and therefore a circuit breaker with the adjustable instantaneous trip function set to OFF would not require one of the means specified in 240.87.

There is also an article on this code revision in April's necplus newsbrief.

http://www.necplus.org/Features/Pages/Newinthe2011NationalElectricalCode24087NoninstantaneousTrip.aspx?sso=0