Accurracy of Modeling Software

[rayman37]

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:

[brainfiller]

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.

[titan]

Which formula did you use for your calculations?

[geh7752]

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.

[SeaBass]

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.

[geh7752]

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 #.