This week’s question is a continuation of last week. Recall the significant change made to the following:

240.87 Arc Energy Reduction. Where the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted is 1200 A or higher, 240.87(A) and (B) shall apply.

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

(B) Method to Reduce Clearing Time. 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
(4) Energy-reducing active arc flash mitigating system
(5) An approved equivalent means

Let’s play “what if�.
What if you were faced with complying with this new code requirement? (Some of you are doing this right now) Which of the options would you use?

• ·Zone-selective interlocking
• ·Differential relaying
• ·Energy-reducing maintenance switch
• ·Energy-reducing active arc flash mitigating system
• ·An approved equivalent means
• ·Depends on the situation

OK, I have read this section over and over but now have to speak up.

Let me get this straight. A device like an energy reduction switch basically acts like an instantaneous trip device. The 2014 text of 240.87 states if the breaker is 1200 A or larger, it has to have something like an energy reduction device (instantaneous). 240.87 says nothing about what if the breaker is already equipped with an instantaneous like most are.

Did I miss something - if I have a breaker 1200A or larger and it DOES have an instantaneous, according to article 240.87, I still need something else for high speed tripping???

Did they really mean this??? If a breaker already has an instantaneous that can be be lowered for high speed tripping, this additional requirement makes no sense.

To me, this seems like a serious error and an exception is needed immediately for cases where the device already has an instantaneous.

Is the intention of 240.87 to be a provision for a failure of the 1200+A breaker (including the instantaneous trip)?

Would not the instantaneous trip of the 1200+A breaker be considered an approved equivalent means?
Would the instantaneous trip of an upstream breaker be considered an approved equivalent means?

I have to agree, that without any numbers given in 240.87, it's hard to judge whether one is within compliance or not. In theory I could have one breaker with a low set instantaneous trip setting be more safe than another breaker with a maintenance switch engaged.

I took a quick inventory and according to the way I read this I presently have 16 breakers in service that are 1200 A or higher. They all have instantaneous trip settings, but they are electromechanical relays and do not have any listed methods to reduce clearing time, leading me to believe that in order to meet the letter of the code I have to upgrade these relays.

I've work for a utility company and have been directly involved in arc flash analysis and reduction. Our breakers operate are on relays that have long time trips or inverse time. 51 ac time overcurrent are normally set high to protect the equipment and ARs automatic reclosures that will reset the circuit and reenergize it 3 times before it locks out. So... our maintenance switches lower the current ratio from the inverse time curve tripping the equpiment quickly at a much less time resulting in less Bolt fault current. Less overcurrent and quicker times resulting in a less exposure from 1584 calculation. ARs are place in manual. This makes our systems less sensitive but much safer for maintenance. Our systems are design to clear faults, such as branches coming across the lines so breaker settings are high. I have taught electrical safety for years, we have also split circuits to lower the hazard. it will be interesting to see this in the NESC chapter 4 or osha 269.

jdsmith and I were discussing this at the IEEE Electrical Safety Workshop this week. I then was able to discuss this with one of the code panel members in a lot of detail. It seems this was one of those “best of intentions� types of articles that might have gone awry. A few points brought out:

One of the acceptable methods is to use Zone Selective Interlocking (ZSI). Well ZSI is not much more than a method to have a signal to cause an instantaneous trip on a device such as the main. If the breaker already has a functioning instantaneous - what’s the point?

A maintenance switch will not help if the arc flash occurs on the main lugs of the main.

No one can give a straight answer if an existing instantaneous can be used as an “approved equivalent means�

The bottom line, is it seems what appears to be a big confusing “oops� was not intentional and is just part of the evolution of new code articles. It sounds like this language will continue to evolve - hopefully for the better.

Using 1200 amps was a compromise and traces back to NEC 230.95 It gives some heartburn because if 1600 A frame breakers are used with the LTP set less than 1200A, this rule still applies. Some may then consider using a smaller frame size but this defeats using all one frame size.

I would encourage our readers and members to consider submitting a proposal (public input) regarding this language for the 2017 Edition of the NEC.

I spoke to someone at NFPA and was told that an instantaneous trip can be considered to be "(5) An approved equivalent means" as long as the AHJ approves of the trip settings.
He told me that the section was previously called "Noninstantaneous trip" which would in prior editions have implied that it excluded instantaneous trips.

There's the rub. The AHJ's in general are not experts in short circuit analysis and coordination studies so making it subject to approval by the AHJ puts a huge burden on them that is kind of unrealistic. Best they can do is ask for an engineering opinion so that some PE can get paid $10K ($500 for engineer's time, $9500 for his/her insurance company).

As a power systems consultant I suppose I should prepare a quotation for $10,000 and a form letter addressing this topic

As several of you have pointed out, the way the vast majority of installations will comply with 240.87 is by employing option (5) with their "approved equivalent means" consisting of an instantaneous trip element set on the affected breaker. The net effect is that for the inspection community the code making panel has:

a) removed the uncertainty around whether a particular breaker is equipped with an instantaneous element
b) created new uncertainty about whether an instantaneous element should constitute "approved equivalent means"
c) if we get approval that an instantaneous DOES constitute "approved equivalent means" now we have to show that we are actually employing an instantaneous element.....oh wait.....