Determination of Cable Sizes for Various Current Ratings
I was opportune to visit a site at Obe, a small community in Benin City, Edo State where I was startled at what I saw the electrician do. Firstly, I observed that there was no registered Engineer on site (Civil/Electrical) all the artisans were all carrying out their duties based on their technical knowhow without an form of design or a qualified Engineer to guide. But whom do I blame? The Workmen? No, The Professional Engineers not on site? No, The successful Businessman Client? YES…
A very learned and successful businessman who has earned his money genuinely and thought it wise to invest in a property could afford to build without the use of professionals.
To avoid digression, I will go straight to what the Electrician did, the client wanted a 3HP package unit AC in his living room (I wonder why?), to my utmost surprise, the cable size I saw him use to run the power supply was a 2.5mmsq cable (Note 2.5mmsq cable has a maximum of 23A current carrying capacity for a 3 or 4 cables, three-phase a.c) . According to him, it is a Nigerian Cable that he was using, hence should carry it.
According to IEE, Table 4E1A, the cross sectional area of the cable and their current carrying capacity was adequately stated.
Using this power formula, we can obtain the required current:
I = P/√3Vcosθ
You can get the appropriate current for the load after applying a standard diversity factor then compare with the IEE Table. For more information on this, a practicing Engineer can be contacted on www.delwit.com/contact-us
Therefore, before any electrician should be allowed to work on your building, kindly ensure an Electrical Design have been properly done by a qualified Engineer who will ensure that all cable sizes for various power and lighting points are within specification. It is always better to be electrically safe.