If you have no idea how electrical circuits work, or what people mean then they talk about volts and amps, hopefully I can shed a bit light.  I’m intending this post to be a simple introduction to electrical circuits for anyone who doesn’t know, but is interested.

I have been thinking recently that there appears to be less professional integrity around than when I first started my career in electrical engineering. Recently the IET has also had a discussion around if engineers should sign an engineering equivalent of the Hippocratic Oath. While I’m not necessarily in favour of swearing oaths, it does illustrate that I’m not the only one thinking about integrity and ethics.

One of the requirements to ensuring that everything works is to have equipment selected, manufactured and verified [tested] to IEC standards. Not all equipment out there meets this requirements. It is the responsibility of the engineers in the procurement and construction process to ensure that only equipment meeting these requirements is used.

If your involved in this activity you most likely already know what to do and have your own methods for approaching this issue. If your new to this or have just been tasked with verifying equipment meets requirements, hopefully this post will get you started.

Ensuring compliance is not complicated, but there are a couple of things you aware of.

Anyone specifying or using electric motors should have a basic understanding how the insulation is related to temperature. Three classes of insulation are in common use (with 'F' being the most common). The image (which is form an ABB catalogue for their low voltage performance motors), shows how the installation is used in practice.

Came across the following site of Siemens technical notes for the first time the other day:

Tech Topics/Application Notes - Siemens

There are a lot of interesting two page type notes on various medium voltage topics – switchgear, circuit breakers, bus systems etc.  It is on the Siemens US site, so many of he note are IEEE/ANSI based. Each topic discusses the standards, application and gives some advice on how to do thing.

I’ve also added a link on the Steven’s Technical Links page, under MV switchgear.

Depending where in the world you work, you are likely following one of two standards

• International Electrotechnical Commission (IEC)
• National Electrical Code/Canadian Electrical Code (NEC/CEC)

The different nature of the two systems make a direct comparison almost impossible. If you do need to work with both systems or transition from one to the other, hopefully the following will make this easier.

The (relatively new) switchgear and control gear standard, IEC 61439 'Low-voltage switchgear and controlgear assemblies' has three methods which can be used to verify the characteristics of an assembly will meet the standard. These are verification by test, verification by calculation and verification by the use of design rules.

The following table (table D.1 from Annex D of the standard)summarizes each characteristic and the allowable options for verification:

Lead acid batteries are cost effect and reliable, making them suitable for many applications. Once serious drawback compared to some other batteries (NiCad for example), is that lead acid batteries are affected by temperature. Lead acid batteries should only be used where they are installed in conditioned environments not subject to excessive temperatures.