The best things in life are free. This is what I felt when I am doing this exercise, comparing results from InterPSS with ETAP.

To verify on how an open source software match up to an expensive commercial software like ETAP, I tried comparing the results side by side. I used ETAP 5.5.6 and InterPSS 1.4.04 in my comparison.

In any project, doing a simple short circuit verification and load flow analysis will save the electrical engineer headaches during testing, commissioning and system reliability testing of the project.

I know some electrical engineers who don't even bother doing a manual calculation because they assume that what they have experienced in their past projects will be the same as their current. This is totally wrong. Every project, despite having similarities have different electrical parameters. Making assumptions and not verifying it mathematically is totally unacceptable.

Short circuit calculation plays a very important role in determining the ratings of electrical equipment. Using software has the advantages, however, to ensure that the software results are correct, hand calculation could be done as a check. Depending on the complexity of the system, hand calculation may be very tedious and impractical.

To demonstrate a simple hand calculation, see the following tutorial at download section.

As the final article on voltage drop and cable selection series, I am now providing a complete worksheet for cable selection based on the IEC standards 60228 and 60364-5-54. I created the worksheet in such a way that it could be printed with your company name, logo, your project, your name, cable number, load description and many more.

Electrical design requires selecting the cable with the correct temperature rating. Designers tend to select the cable with the highest temperature rating, this is not acceptable as the first cost of the project will be affected considerably.

A cable temperature rating is based on the type of material used for its insulation. In this article, we shall be discussing how to correctly select the cable temperature rating for certain installation requirements based on the environmental condition.

In our example in Voltage Calculation - Part 2, we have only considered a single cable and checked only the voltage drop at starting. In actual practice, we shall be comparing several cable sizes, selecting the cable that provides optimum design consideration.

In this example, we shall be using several cables from 35 mm2 up to 120 mm2. Likewise, we shall be considering, not only the starting condition but the running condition of the motor as well. You might be asking, why we selected a motor in our example. The reason, a motor is a dynamic load. A motor circuit load varies from the starting to the normal running condition, thus there will be multiple considerations when selecting the cable for a motor circuit.

We shall be presenting an IEC standard equipment in our sample calculation.

A 120 mm2 3core XLPE insulated cable 120m in length supplies a 110 kW induction motor that has a starting current of 6 times the full-load current of 180 amps. The starting power factor is 0.25 lagging.

Cable selection is an important part of electrical installation design. Selecting the correct size of cable could lower initial cost, lower operating cost, better voltage regulation notwithstanding the safety factor.

The primary objective of earthing (or grounding as referred to in North American standards) is safety, to reduce risks to both human life and installations. The principles of electrical earthing are agreed upon internationally, though in practice, there are differences as to how these principles are best achieved.

Electrical systems were not always earthed. The first systems were unearthed ones with no earth reference at all. Even though such systems still exist in specific areas, they are the exceptions rather than the rule and by and large, some form of earthing is adopted for all power systems.

IEC 60079-0 specifies the general requirements for construction, testing and marking of electrical apparatus and Ex components intended for use in explosive gas atmospheres.

Unless modified by one of the parts in the IEC 60079 series, electrical apparatus complying with this standard is intended for use in hazardous areas in which explosive gas atmospheres, caused by mixtures of air and gases, vapours or mists, exist under normal atmospheric conditions of

• temperature –20 °C to +60 °C;
• pressure 80 kPa (0,8 bar) to 110 kPa (1,1 bar); and
• air with normal oxygen content, typically 21 % v/v.

The requirements for Electrical apparatus for explosive gas atmospheres have been detailed in the IEC 60079 series.

This article, an extract from IEC 60079-10, will be the first of a series of articles discussing the requirements for explosive gas atmosphere electrical installations. To understand better the requirements for hazardous areas installations, IEC 60079-10 provides the classification of explosive atmospheres.

The objective of IEC 60079-10, Classification of hazardous areas, is to set out the essential criteria against which the risk of ignition can be assessed, and to give guidance on the design and control parameters which can be used in order to reduce this risk.

The IEC 60364 (Electrical Installations of Buildings) and the ANSI/NFPA 70 (NEC) are the bases for most national wiring rules throughout the world.

The NEC evolved along with the growth of electrical systems in North America more than 100 years ago to establish a uniform level of safety, while the development of IEC 60364 documents ensued in 1969 for reasons of harmonization of electrical installation rules to facilitate trade among European countries.

IP Rating Chart

IEC 50529 applies to the classification of protection provided by enclosures for electrical equipment with a rated voltage not exceeding 72.5kV.While this system is suitable for use with most type sof electrical equipment, the manufacturer of the equipment should still be consulted to determine the degree of protection available and the parts of equipment to which the stated degree of protection applies.