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 Post subject: Accurracy of Modeling Software
PostPosted: Tue May 25, 2010 4:11 am 

Joined: Thu Apr 02, 2009 4:33 pm
Posts: 29
Location: OH
Is SKM, ETAP, and Easypower accurrate? I tried out all 3 softwares and Easypower more closely matches my hand calcs for short current. Etap and SKM are within a few hundred amps of each other. When modeling in ETAP, when you pick the wire in the easypick window, using non magnetic, the choices are limited to rubber 2 NEC. SKM lets you pick non-magnetic THHN etc. Does this really make a difference in the calculations? :confused:


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PostPosted: Tue May 25, 2010 7:42 am 
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It is good that you are taking them all for a "test drive" and compare them. The conductor data can make a difference.

The insulation has more to do with the thickness which can affect the X value of the impedance. The conduit being Steel (Magnetic), Aluminim (non-magnetic), or non metal also makes a difference.

The Magnetic vs. Non-Magnetic affects the X value and the non metallic (not to be confused with non-magnetic) affects the R value (think skin effect).

In the end, the more accurate the better. However the bottom line is you probably have a PPE level in mind and if your calculations put you well below the level of PPE you are using, accuracy is likely not going to get you into as much trouble. If however, you are close to the rating of the PPE and are off a little bit in the wrong direction - that could be a problem.

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PostPosted: Tue May 25, 2010 11:41 am 

Joined: Thu Apr 29, 2010 10:49 am
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Which formula did you use for your calculations?


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PostPosted: Wed May 26, 2010 4:55 pm 
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I use etap 7.1 and have complained to them about their confusing cable library that quite frankly, sucks, and as far as I can tell doesn't agree with any NEC table I can find. It seems to be a mix master of cable manufacture's cut sheet ratings. Something I found disappointing in a high end analysis program. They claim it is being rewritten for the upcoming Etap release sometime late summer. Etap does allow you to create a user cable library. So I build one based on the NEC tables. I did test drive EasyPower and found their device and cable library's well documented, user friendly and accurate. Although EasyPower lacks some of the advanced customizing features of Etap, especially with arc flash reporting.


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PostPosted: Thu Aug 26, 2010 3:55 pm 

Joined: Thu Aug 26, 2010 3:49 pm
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With respect to accuracy, all major programs (EDSA, SKM, ETAP, ESA) are or should be ISO certified. I can only speak for EDSA as that is the one I use.


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PostPosted: Mon Aug 30, 2010 9:28 am 
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Etap is ISO certified. After test driving Easypower, Etap, SKM and doing the IEEE 1584 calculation long hand I found none of the calculation matched exactly. Much has to do how each program looks at cable impedances (using mfgs spec sheets or NEC), conduit type (mag or non mag), protection device clearing time and fault currents. All of which can change the incident energy numbers. I found using none of the programs changed the IE numbers for a given case enough to jump to a new Cat #.


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PostPosted: Fri Sep 17, 2010 10:37 am 

Joined: Wed Sep 15, 2010 9:56 am
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Modeling Software Accuracy

I actually have used all 3. I like ETAP much more than the others for all aspects of the software except cable library interface. They do have a lot of cables in there, but you have to select the different ratings to see them. They did tell me they were working on that too but I guess we shall see when it comes. In terms of accuracy, they are all ISO certified but that is just because of documentation. ISO shouldn't be the only guide to accuracy. Accuracy should be the number one factor in terms of arc flash calculations, so I would suggest you to do research on that. That is what the Nuclear industry uses to decide which software they go with. That is their main factor.


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