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Dr. Johannes Auret is a director and explosion prevention specialist at Explolabs and Certex. He has a PhD in engineering, and worked for the CSIR and SABS before joining Explolabs in 2001. He is active in industry standards development and has convened various working groups. Dr. Auret has published numerous technical articles and is a regular speaker and author. Tel: 011 316-4601, johannesa@explolabs.co.za. He answers questions on explosion protection… (more)

Advice on, among others, load calculations for chillers; extractor fans in toilets; double-pole switching for equipment; back-up for theatre curtains and calculating total load on lighting circuits… (more)

Q: I am installing lightning protection at a cellphone site. How do I calculate the number of rods required to achieve a meter reading of 10 ohms? The ground is very damp. A: Lightning protection is a highly specialised field. The design installation of lightning protection must be done according to SANS 10313, the South African standard for protection against lightning, “Physical damage to structures and life hazard”… (more)

Q: What is ESD? A: Electrostatic discharge (ESD) is the sudden flow of electricity between two objects caused by contact. One of the causes for ESD is static electricity. Familiar examples of ESD include the shock we receive when we walk across a carpet and touch a metal doorknob, and the static electricity we feel in winter from certain clothing. The threat of ESD looms everywhere in electronic work areas – floors, chairs, work surfaces, packaging materials, plastics and papers, these all give rise to static electricity… (more)

Michael Garnham has a BEng in electrical engineering and a BSc in information technology and is the manager of the South African Profibus and Profinet Training and Competence Centre. Feedback is welcome: michaelg@idx.co.za. Q: I don’t have Profibus, but how can I make use of its fortes? A: It’s not uncommon for users of other fieldbuses to want to implement devices specific to Profibus… (more)

Question: Would it be OK to replace the fuse board in an existing domestic installation with a distribution board with a 60 A / 30 mA earth leakage main switch? Answer: Ideally, all fuse boards should be replaced with DBs. However, despite fuses not being permitted in new domestic installations, they may be used in existing installations, provided that this is not contrary to reasonable safety. This would provide the required overcurrent protection and correct labelling… (more)

This begins a series of Q&A on a variety of topics of interest to our readers, starting with automation. Gerhard Greeff, Manufacturing Enterprise Solutions Association (MESA) Southern Africa answers the following questions. Q: With the emergence of M2M technologies, do you think the manufacturing industry is ready for a true cloud-resident MES?… (more)

Question 1: I must replace a 240 V domestic fan in a bathroom. The existing fan was installed some 15 years ago and no supplementary bonding exists… (more)

Question: When installing an all-steel cable management structure (tray, baskets and supports) in an all-steel container for telecoms cabling (48 V DC and signal cables) with AC power and lighting – all contained in separate PVC trunking and conduit, is cross bonding required between all component parts of the DC cable management?… (more)

Question: We must install lightning protection services (LPSs) at a mobile phone site. How do I calculate the number of rods required to achieve a meter reading of 10 Ohms?… (more)

Our experts solve readers’ technical problems — Electrical contracting often presents problems which, when solved by experts and shared in a forum, can be turned into learning opportunities. Working in co-operation with the ECA(SA) and other experts, Vector now provides such a forum. Our expert for this issue is Cecil Lancaster… (more)

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