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Who Uses Selective Coordination?Author: Chris B Posted Date: 3/15/2010 4:29:10 PM
What this all boils down to, a lot of you would ask, is this - who does this even affect? Here's a simple list with four specific people that need to follow selective coordination guidelines.
1. Designers: Those who are making the plans for any structure obviously need to account for the essentials in electrical systems - branch circuits, feeders, and sub-feeders. They need to be planning effective selective coordination for every single thing.
2. Plan Review/Inspectors: Those who review the original design plan have a critical job. Inspectors need to look at power systems, determine whether they are compliant or not, and correct any problems according to this.
3. Engineers: These are the ones who will have to stamp any documents detailing the design, providing that they are designs that actually achieve proper selective coordination.
4. Contrators: Their role here would be installing the electrical system as it was designed. Optimally, again, the system was designed originally with good selective coordination in mind.
All of these types of people are affected by the NEC in that they play a huge role in compliance issues. The 2008 NEC has a purpose, like I mentioned in the beginning, to improve safety conditions and avoid panic-inducing blackouts. Comments (0) | Leave Comments |  Permalink selective coordination, nec 2008, designers, inspectors, engineers, contractors, electrical systems, safety, blackouts, power
Effective Selective Coordination Set-ups - Pt. 2Author: Chris B Posted Date: 3/12/2010 7:49:38 AM
As I mentioned in my last entry about SC, there are a couple of methods that are most common for figuring out proper selective coordination. With any of these, the results should be interpreted correctly by a qualified individual.
1. Short-circuit current calculation study: This method is appropriate if circuit breakers are being used. It involves plotting time-current characteristic curves and then interpreting that data properly. An engineer can look at this information and determine whether or not selective coordination has been achieved.
2. Adhering to selectivity ratios: You'll go this route if fuses are being used. Just use fuse types and ampere ratings that adhere to the particular manufacturer's selectivity ratios. This is the easier method of the two.
Cooper Bussmann, however, makes it even easier to design and install systems with proper selective coordination. They publish Fuse Selectivity Ratio Tables for people to refer to. All that's required is that you make sure all fuse types and ampere rating ratios for the mains, feeders and branch circuits meet or exceed these listed selectivity ratios. You then can leave fuses where they are or adjust things accordingly. There's nothing else to analyze, and no other settings to tweak with!
If you'd like to get an even better grasp on Bussmann's method for meeting SC, you can read more detailed information here:
Comments (0) | Leave Comments | Permalink cooper bussmann, fuses, circuit breakers, selective corrdination, calculation, selectivity ratios, electrical distribution, quality, power, blackouts, faults, nec 2008
Effective Selective Coordination Set-ups - Pt. 1Author: Chris B Posted Date: 3/11/2010 10:19:06 AM
It doesn't matter much what kind of building you're talking about; an office building, plant, high-rise apartment complex, hospital, or a theater. You need a quality electrical distribution system in all of these. There's nothing more effective than a power failure in stirring up anxiety, wreaking havoc, and causing overall panic because of its unexpectedness. It's exactly why the NEC has called for Selective Coordination for such a long time.
Without properly isolated faulted circuit from all of the other components in an electrical system, you're setting yourself up for many guaranteed power blackouts. Here's a pretty clear illustration of what effective selective coordination is able to do:
The system on the right is obviously 100% more desirable. You have only one circuit (the one with the fault) being affected. The rest of the power system isn't even touched - nothing, nada, zip. There's absolutely no interruption in the rest of the system. And that, in turn, means no unneeded risk of a blackout.
Next time, I'm going to cover some of the popular methods used in determining selective coordination quality in an existing system. Stick around for that because I'll be giving some thoughts on what's really the best way. Comments (0) | Leave Comments | Permalink buldings, selective corrdination, electrical distribution, quality, power, blackouts, faults, nec 2008
Fuses and NEC 2008 ChangesAuthor: Chris B Posted Date: 3/9/2010 5:09:56 PM
Recent catastrophic events like hurricane Katrina and 9/11 have made a lot of people take notice, especially those behind the National Electric Code. As part of a huge shift in focus toward life safety (like new AFCI/GFCI and tamper-resistant receptacle requirements), there have been a number of changes in regard to power devices. The events I mention above were monumental in drawing attention to the need for system load reliability. Whenever part of a building is damaged or failing, a key objective is clearly maintaining power to the "vitals" as long as possible.
This is where "selective coordination" comes into play. Selective coordination is the act of isolating a faulted circuit from the rest of an electrical system, which is the best way to eliminate unnecessary power outages. You do this by using overcurrent protective devices that have ratings and settings just like a particular overcurrent condition.
For your own reference, here's a quick list of applications where selective coordination is required per the NEC:
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Healthcare facilities, which have essential electrical systems like critical branches and life safety branches. (Article 517.26)
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Certain types of elevators (Article 620.62)
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Emergency systems in places where people frequently assemble, such as hotels, theaters, sports arenas, health care facilities, etc. (Article 700.27)
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Legally required standby systems, like those that serve loads in heating and refrigeration, smoke systems, communication systems, ventilation systems, sewage disposal, and other processes where any interruption would be hazardous. (Article 701.18)
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Critical Operations Power Systems with loads for communication and data centers. (Article 708.54)
I'll pick up next time with more detail on what selective coordination is, and what compliance means in light of NEC. Comments (1) | Leave Comments | Permalink bussmann, fuses, selective coordination, applications, nec 2008, national electric code, power, safety
9/6/2010 7:29:24 PM
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