Inspectors Checking for Selective Coordination

[davidr43229]

I have a question here. Are any Inspectors checking for Selective Coordination, as provided in many of the NEC articles, including Elevators. I know the city of Phoenix is and sevral parts of Fla are.
Are you asking for submitals of the curves? If not, how do you deterime that a circuit is selectively coordinated?
Just curious.

 

[bphgravity]

I am.

I perform all the electrical plan review for te City of North Port here in Florida and check for the selective coordination study when required (517, 620, 700, 701) Once we the project gets to inspection, compliance with the approved plans is verified.

Generally, I look for some sort of time-trip curves and product specifications, in other cases, a signed and sealed letter by the engineer is sufficient.

 

[davidr43229]

Bryan,
Thank you for that. When you look at the time current curves, do they go below the .1 second level ie; .01 seconds?

 

[bphgravity]

At this particular time, we are not requiring coordination in the instantaneous regions for three primary reasons:

1. Bolted fault currents at those levels are highly unlikely.

2. AHCA only requires coordination in the short time and long time regions above 100ms.

3. Section A.6.5.1 of the NFPA 110 states, "It is important that the various overcurrent devices be coordinated, as far as practicable, to isolate faulted circuits and to protect against cascading operation on short circuit faults. In many systems, however, full coordination is not practicable without using equipment that could be prohibitively costly or undesirable for other reasons. Primary consideration also should be given to prevent overloading of equipment by limiting the possibilities of large inrushes due to instantaneous reestablishment of connections to heavy loads."

I check coordination to the 100ms level, anything beyond that is at the discretion of the design professional (engineer) whom is ultimately responsible for proper system operation.

 

[davidr43229]

Bryan,
Thank you for your explaination.

Section A.6.5.1 of the NFPA 110 states, "It is important that the various overcurrent devices be coordinated, as far as practicable, to isolate faulted circuits and to protect against cascading operation on short circuit faults

If you are checking above the 100ms range, which is 6 cycles or more, which is the overload region of most overcurrent protection devices, how are you checking for the protection against cascading operation on the shortcircuit section of that overcurrent protection device in "any" available fault condition?

I ask this due to some overcurrent protection devices totally clearing within the .01range in a short circuit. Isn't that important also?
Just my $.02

 

[davidr43229]

NFPA 110?s scope does not encompass the full emergency system. It encompasses from the generators to the load side terminals of the transfer switches. The NEC covers the entire system. Also, NFPA 70 (NEC) trumps NFPA 110.
Would you not agree?