700.27 and 701.18: Local Amendment

[don_resqcapt19]

Charlie,
The ROP and ROC for this issue are on line at NFPA as this was a 2005 code change. Here is the original proposal.

13-135 Log #3034 NEC-P13
(700-28)
Final Action: Accept in Principle in Part
Submitter: Todd Lottmann St Louis, MO
Recommendation:
Add the following to Part VI of Article 700:
700.28 Selective Coordination.
All overcurrent protective devices in emergency systems shall be selectively coordinated to ensure proper isolation and localization of
a fault by the overcurrent devices closest to the fault condition and preventing loss of power to other unaffected parts of the emergency
system.
Substantiation:
The requirements contained in Article 700 focus on providing a reliable emergency system that will be operational when called upon
for its use as supported by the maintenance and testing requirements in 700.4. The critical nature of the dependence on emergency
systems for safety of human life, as stated in the scope, supports these requirements. This article specifically mandates that the
emergency circuits be separated from the normal circuits as shown in 700.9(B) and that the wiring be specifically located to minimize
system hazards as shown in 700.9(C), all of which reduce the probability of faults or failures to the system so it will be operational when
called upon. With the interaction of this article for emergency lighting for egress, it is imperative that the lighting system remain
operational in an emergency. Failure of one component must not result in a condition where a means of egress will be in total darkness
as shown in 700.16. In addition, the allowance to bypass the alternative source ground fault protection for equipment shows the
preference for system operation in the event of an emergency and the fact that if a fault occurs we do not want the whole system to go
down and create an unsafe situation for human life. Selectively coordinated overcurrent protective devices will provide a system that
will support all these requirements and principles. With properly selected overcurrent protective devices, a fault in the emergency
system will be localized to the overcurrent protective device nearest the fault allowing the remainder of the system to be functional as all
the previously mentioned requirements intend to do. Due to the critical nature of the emergency system uptime, selective coordination
must be mandated for emergency systems. This can be accomplished by both fuses and circuit breakers based on the system design and
the selection of the appropriate overcurrent protective devices.
Panel Meeting Action: Accept in Principle in Part
Delete 700.25 FPN and add New Section 700.28 to read as follows:
"700.28 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent
protective devices."
Panel Statement:
The panel agrees that selective coordination of emergency system overcurrent devices with the supply side overcurrent devices will
provide for a more reliable emergency system. By excepting in principle this proposal the FPN in Section 700.25 is no longer needed to
alert users about selective coordination. The part the panel accepts is selective coordination of emergency systems. The panel's wording
accomplishes the intent of the submitter without adding design aspects of selective coordination into this section.
Number Eligible to Vote: 14
Ballot Results: Affirmative: 13 Negative: 1
Explanation of Negative:
ELKINS: Perfectly selective coordination is not always possible for all fault current levels when protection is provided by common
molded case circuit breakers. This requirement will force the use of fuses which may expose workers to energized parts during
replacement or the use of more sophisticated breakers with complex settings which are more likely to be mis-set resulting in false trips.
Reliability and safety of these services are best served by the existing NEC FPN wording which alerts the user to the need for selectivity
when possible.

 

[charlie b]

The ROP and ROC for this issue are on line . . .

Thanks, Don. I printed out the six pages that had the related proposals from the 2008 cycle, and will read through them when I get a spare moment. I do see what you meant when you said (earlier) that the original proposal had no real substantiation that the change would solve a real problem.

 

[rbalex]

Since Don sent the link to the ROP/ROC page, I'd like to make another recommendation. Review the Drafts. The Drafts are supposed to reflect the revised content of the NEC if there were no other changes accepted during the Comment stage. Reviewing them will often disclose how the ?mischief? started since the Drafts include the Proposal number that initiated the revision. Unfortunately, the Comment stage often creates mischief of its own and commonly is where unintended consequences arise.

 

[steve66]

That sounds exactly like what a breaker guy said at a presentation I attended, but then the fuse guy got up and said, "gee, we don't have any problems like that with our products".

That might be true, but the fuse people have other problems that the breaker people don't. Does anyone really want to use fuse panels instead of breaker panels for all new emergency branch circuits? They are too expensive, too large, its too easy for the janitor to replace a 20A with a 30A, and if a fuse does blow in an emergency situation - who has time to go look for another one.

I think there is actually a code section in NFPA 99 that says you should give consideration during design to how fast power can be restored after an outtage. So by using fuses to comply with one code, we are breaking another code.

Steve

 

[weressl]

By requiring total coordination, you are ignoring many other aspects of electrical design, including arc flash hazzards, and possible damage to equipment and feeders.

It also ignores the fact that we are frequently adding onto existing systems, and adding into existing buildings. Many times, you just can't achieve total coordination without replacing the entire system - which is usually impossible or impractacle.

I have seem several places where other safety aspects would have to be comprimised to achieve total coordination. Is that what we really want?

Steve

There could/should be a leeway for existing systems and the upstream modification to be required. On the other hand if the coordination could have been achieved within practical limits and the lack of it resulted in a personal injury or death then the failure to do so would be ruled as negligence.

I had some difficulty with understanding the poll question, but reading the posts seem to mean that coordination under 0.1 second could be omitted.

 

[charlie b]

On the other hand if the coordination could have been achieved within practical limits and the lack of it resulted in a personal injury or death then the failure to do so would be ruled as negligence.

I can?t disagree in principle, except perhaps to suggest ?could be ruled? for ?would be ruled.?

But it is also a matter of degree of risk. If you are driving your car, and someone starts to run a red light, and they have to swerve to avoid hitting you, and instead they hit a tree and are injured, then can you not be called to answer for having taken an unwarranted risk? After all, you had to know that auto accidents kill and maim tens of thousands of people every year. Despite knowing the risks, you choose to drive to the grocery store for no better reason than to buy a carton of milk. Had you not been in the intersection, my client would not have needed to swerve, and their car would not have hit the tree.

My point is that if we decide that a postulated event is an acceptable risk, and if the event does actually happen, does that render our previous judgment invalid?

I had some difficulty with understanding the poll question, but reading the posts seem to mean that coordination under 0.1 second could be omitted.

That is the proposal that is under consideration for inclusion in the Seattle Electrical Code.

 

[weressl]

I can?t disagree in principle, except perhaps to suggest ?could be ruled? for ?would be ruled.?

You're absolutely right, I should have used 'could'.