First of all for today I hope you all enjoyed the day off to celebrate the annual Labor Day holiday. You all work so hard an a day off to celebrate that hard work is deserved.
Todays news letter has to do with Arc Flash reduction, which is a requirement of the Code to help reduce an arc flash incident if one was occur when someone was working on a live “Hot” piece of switch gear. The methods described in the article would allow someone to work on a main switch or disconnect that is hot and set the breaker or by-pass switch to maintenance mode so that if an incident was to occur it would clear almost instantaneously reducing the incidents arc flash. Thereby giving the worker added protection from a possible disastrous arc flash incident.
This section first introduced in 2011 has been updated in the 2014 giving us some additional ways to reduce the hazard for workers who are working within the Arc Flash Boundary as defined NFPA 70E. Based on the 2014 guide lines for mitigating the hazards of working on energize switch gear, there are now several ways to limit the time a circuit breaker will take to shut off reducing the arc flash incident. All of these methods will require you to research the methods to find the one that works for your installation.
A few contractors have asked about ways to work around this code article, especially ones who are working on high end residential projects. Homes with 1200 ampere services or larger. One way would be to have multiple mains smaller than 1200 amperes or use fused disconnects for mains, both which are not covered by this article.
When designing and building a service this large you would have to have an engineer involved because of Florida statute 471.003 h which only allows an electrical contractor to design and build a residential services up to 600 amperes at 240 volts, and commercial services up to 800 amperes at 240 volts.. So next time you encounter a large service (1200 amperes or larger) commercial or residential maybe you can suggest a couple of smaller mains rather than going with the larger one.
See the Code section 240.87 below:
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 mitigation system
(5) An approved equivalent means
All of the ways to minimize an arc flash incident will have to be done under engineering supervision in order to meet one of the five methods required in the above Code section.
Till next time be safe work safe.
Jake
