Working Knowledge by Terry Mackenzie Hoy looks at the electrical industry from an electrical engineer’s perspective and offers valuable advice to everyone in the electrical profession – including young apprentices, self-employed electrical contractors and electrical engineers. With about 40 years in the industry, Terry draws on some of his own experiences as the background to his columns and to illustrate his point. He encourages integrity and ethical business practices and, above all, safe working practices. Sometimes humorous, always honest, Terry’s columns cover topical issues in a pragmatic, no nonsense style and, when necessary, he shoots from the hip.
January 2016
Terry says that, for electrical contractors, cash flow is one of the biggest problems facing small electrical businesses and he gives some advice on how to keep the wolf from the door. Read more...
February 2016
This column discusses PILC and XLPE cables and the problems associated with ‘dendritic water trees’. If you are going to use XLPE cable, use South African made products, says Terry. Read more...
March 2016
In March, Terry looks at the ‘system’ whereby, when tendering for a contract, contractors name an amount for completing work on time, another amount for working safely and a further amount for good quality of work. If the targets are met, they are rewarded, however, if the targets are not met, they are penalised. Read more...
April 2016
This column sees Terry talk about motor control centres and he gives some interesting background to the development of motor control centres. “A well-designed MCC is a pleasure. And a badly designed one is a nightmare. An overdesigned one is silly,” he says. Read more...
May 2016
In his May column, Terry delves into motor control systems and the importance of remote starting and stopping, which, says Terry, is a matter for careful consideration. Read more...
June 2016
In his June column, Terry talks about energy contractors and gives some pointers as to what constitutes good energy saving and what doesn’t. Read more...
July 2016
In his July column, Working Knowledge, Terry relates three tales that summarise why electrical contractors should regard personal safety and the safety of all work on site is extremely important. Equally important is to remember that lawyers make money out of one party claiming from another. No matter how much time elapses or how unlikely the claim, they will claim if they can. And they will claim from you. Read more...
August 2016
In his August column, Terry Mackenzie Hoy discusses ‘the grid’. “We can comprehend the apparent scale of the National Grid when we consider that the energy consumption of South Africa is the same per capita as the combined consumption of Botswana, Namibia, Zambia and Zimbabwe.” Read more...
September 2016
In his September column, Working Knowledge, Terry Mackenzie Hoy discusses a situation he encountered with a counterfeit relay and explains the Law of Delict when it comes to installing counterfeit devices – even if this is done unknowingly. Read more...
October 2016
In his October column, Working Knowledge, Terry Mackenzie Hoy indulges in a little retrospection about some hair-raising experiences he has had during his long career, and appeals to young electricians to “observe and think” when confronted with anything that doesn’t make electrical sense. Read more...
November 2016
In his November column, Working Knowledge, Terry Mackenzie Hoy says that most municipalities have finally accepted that there are people who would like to generate their own power; and the only stable, reliable way to do it, is to connect it to the municipal grid. “Having accepted that private generation will occur (it is now called ‘embedded generation’), there are a whole lot of guidelines that have been published, which contain recommendations from NRS and various municipalities,” he writes, and adds:” This is where the paint hits the carpet.” Read more...
December 2016
In his final column of 2016 Terry Mackenzie Hoy says that many emerging contractors underestimate the enormous amount of paperwork associated with getting a contract. And, when the correct paperwork is not submitted, this can delay payment of invoices and impact the cash flow. Read more...
January 2017
In his first column for 2017, Terry Mackenzie Hoy predicts that more electrical contractors will get involved in the installation of solar PV power generation projects – something many have been reluctant to do because the technology is regarded as ‘new’ and they are unfamiliar with the technical terms. Read more...
February 2017
In his February column, Terry Mackenzie Hoy highlights a common problem in South Africa – that, although it is a requirement of the OHS Act that work on an electrical installation must be supervised by a registered installation electrician, this doesn't always happen. Read more...
March 2017
In this month’s column, Terry Mackenzie Hoy discusses two things that need to be considered when choosing a cable to supply a load: the current handling capability of the cable and the volt drop at the point of connection to the load. The current handling capability of cable is to be found in tables in SANS 10142; but all is not as simple as it sounds. Read more...
April 2017
This month, the inimitable Terry Mackenzie Hoy apologises to our readers for a mistake in a previous column, thanks Kevin Welch of UIC Automation (Pty) Ltd. for pointing out the error and then moves on to discuss electric motors, more specifically single phase motors. Read more...
May 2017
Terry Mackenzie Hoy reminds us in this issue how very important it is to follow safety procedures to the letter. Currently we use a ‘permit system’ to ensure that any work conducted in a plant is done so in a safe manner by isolating valves, electrical supplies, compressed air, et cetera. This works well if the procedure is followed ... that is until the shift changes and the operator who issued the permit is not the one who signs off. Although other systems can be put in place, they are also not fool proof. In his next column, Terry will outline what he believes is a 100% safe permit system. Read more...
June 2017
This month Terry Mackenzie Hoy tell us how to test a generator, giving detailed step-by-step guidelines for both old and modern generators – rated at 100 kVA or less as well as those rated at more than 100 kVA – while stressing the importance of applying caution at all times. Read more...
July 2017
This month Terry Mackenzie Hoy clarifies motor ratings and voltages. When a motor is labelled ‘400 V / 380 V 3 ph’, the assumption is that it is not the same as another motor with a label that reads ‘400 V 3 ph’. He assures us they are the same motor and reminds us that there is a wide tolerance for the voltage range over which a motor will continue to operate satisfactorily. In general, he emphasises, motors can operate within +/- 5% of their nominal rating (i.e., 400 V or busbar voltage rating). Read more...
August 2017
Having recently helped a colleague with a distribution board that just ‘kept tripping’, Terry Mackenzie Hoy uses this column to remind us how to approach the problem of unexpected earth leakage trips. He suggests we start with a few standard questions: Has anybody recently worked on the distribution board? Have you recently connected a new power point? How old is the distribution board? Have you recently purchase a new appliance? As always, there is other advice! Read more...
September 2017
In his training and development column, Nick Du Plessis reminds employers of the Occupational Health and Safety Act of 1985 which outlines the general duties of employers to their employees. Nick stresses the obligation employers have to ensure employees are provided with training, information, instruction and proper supervision, with specific reference to using tools correctly. Read more...
October 2017
A good maintenance person is worth paying for, says Terry Mackenzie Hoy. In his column, Terry focuses on lighting and discusses various lamps and their maintenance issues. He points out common errors made by people who don’t know enough about lighting or lights. Terry recommends that we do not ask lighting suppliers or interior designers what lights to install but, instead, ask a good lighting technician or an experienced electrician. His golden rule: make the Monday before 16 December fluorescent re-lamping day! Read more...
November 2017
To end off the year, Terry Mackenzie Hoy discusses transformers in electrical installations and reminds us that when it comes to transformers, all is not as simple as it seems. There are three broad categories of transformers, namely, power distribution transformers, voltage transformers and current transformers. Power transformers are made to SANS specification SANS 60076-1:2011 Power transformers – Part 1: General. Standard sizes are 200 kVA, 315 kVA, 500 kVA, 630 kVA, 800 kVA, 1 000 kVA, 1 250 kVA, 1 600 kVA, 2 000 kVA and 3 150 kVA and most distribution transformers have a primary voltage rating of 6 600 V, 11 000 V, 22 000 V or 33 000 V, three-phase. Terry outlines the variations in power distribution construction and provides a checklist of things to bear in mind. Read more...
February 2018
Sherlock Holmes (the fictional private detective) famously said, “When you have eliminated the impossible whatever remains, however improbable, must be the truth”. In his column, Terry Mackenzie Hoy tells us how, with a production manager and a general manager breathing down your neck, you find the fault in a control or distribution board when you do not have the drawing. Or you do, but that drawing is out of date. To start with, you ask said managers to move away. You then get a stool, good light, roll down your sleeves and start at the beginning. Read more...
March 2018
Terry Mackenzie Hoy started in engineering when he was 26-years-old and is now 62. In this time he has seen many developments in 11 000 V circuit breaker technology, and in this issue he shares some of them with our readers. Read more...
April 2018
Terry Mackenzie Hoy was recently asked a pertinent question by a contractor friend; what should their son do upon leaving school? In his column this month, Terry offers some valuable pointers for the younger generation. Read more...
May 2018
When Terry Mackenzie Hoy started work in his 20s, there was no real way of varying the speed of an ac motor. It was not too difficult to vary the speed of a dc motor – you just adjusted the field voltage or the armature voltage or both. Yet ac motor speeds were difficult to adjust. The desirability of adjusting ac motor speeds was one of cost – dc motors were more expensive and had higher maintenance costs compared to ac motors. Read more...
June 2018
This month Terry Mackenzie Hoy states that the future of cars will be in some way electric. The general style of technology for an electric car drive was a dc motor driven off lead acid batteries; the dc motor drove the wheels directly. The result was a heavy car with an awkward centre of gravity which made the suspension a challenge and there was very little protection from collision related injuries. Yet things have changes, and in this month’s column he discusses oh electric vehicles will impact on the work of the electrical contractor. Read more...
July 2018
This month Terry Mackenzie Hoy recounts a recent interaction with one of his engineers to encourage the industry to try fix the something that breaks before throwing it away. Throwing things away should be the last resort, not the first. Although, fixing things can be a time consuming exercise, it is always a good idea to see if there is an obvious problem which can be fixed. A bit of logic helps, too. If something stops working, ask, why now? Look for the basics. Read more...
August 2018
This month Terry Mackenzie Hoy implores electricians not to do electrical work which does not come through your employer or business. Apart from the legal ramifications, doing electrical work for friends, family and neighbours is a potential minefield of problems – it is a no-win situation, so don’t even try. Read more...
September 2018
This month Terry Mackenzie Hoy discusses how, in earlier years, consulting engineers loved any project that required the installation of an 11 000 V/400 V power distribution transformer because the consulting fees were a percentage of the contract value and, since power transformers were comparatively costly, a power transformer or two would increase fee income handsomely. Read more...
October 2018
This month Terry Mackenzie Hoy states that the simple bottom line is that when a consumer is connected to a power supply, it is desirable, from the point of view of the supplier, that the consumer pay for the electricity consumed. He discusses the measurement of electricity and fluctuating energy loads. Read more...
December 2018
Motor control circuits have been around for decades, much without change. Having said this, there are various people in the industry who will insist on ‘fiddling’ with established circuit design. They fit the motor control circuit with smart electronics that count the number of times the motor starts and send the value of the motor current via a telemetry link to a control room which has pretty diagrams showing how the motors in the plant are operating… all of which is unnecessary. Simple is better. Simple is reliable. Simple circuits work well. Read more...
March 2019
This month Terry Mackenzie Hoy discusses the requirements for a Certificate of Compliance (CoC) for an electrical instillation and its inherent problems; if you come across a switchboard that has been modified and you have to install a new circuit breaker, do you write out that your certificate only covers the new circuit breaker or do you tell the client that the whole board has to be wired to specification? Tricky. Read more...
April 2019
This month Terry Mackenzie Hoy discusses how, at this time of load shedding, the authorities switch off largish blocks of load and switch them on again. In general, energising and de-energising a circuit where the load is a few megawatts is no big deal, yet so-called surges and spikes on a power system, which actually occur very irregularly, become more frequent and damaging when the supply authority is switching large blocks (tens of megawatts) of load. Read more...