Feedback - your letters

Covers for mains sockets has received a twined prong reaction from you; both positive and negative, colour coding medication and the half full half empty debate has an interesting twist. Of course this is just a sample so read on to receive maximum benefit.

When the wind doesn't blow

Recent issues of E&T have included some excellent letters about renewable power, some from engineers with first-hand experience of directing energy to fulfill the vagaries of UK demand. I can understand the frustration caused by the intermittent supplies from wind power sources. The logistics of providing a constant level of power from installations using, say, 100 turbines of 2MW rated capacity each, where the power generated is anywhere between maximum and zero over a quite indefinable period, must be horrendous. Obviously, quick reaction backup power must be available.

Understanding the power generated from this source is obscured by the terms used. The wind turbine industry quotes "installed capacity" as one of its yardsticks. A typical turbine might be rated at '2MW from a 25m/s wind (50 knots)'. This is the top-end of the UK wind scale and approaches cut-off point when the turbine has to be shut down. Winds of 10m/s (20 knots) are more common.

This is crucially important as wind turbines generate power proportional to wind speed cubed. A 10m/s wind will generate 130kW of power, nowhere near the 'installed capacity' figure. Winds below 5m/s are insignificant and, while the turbine blades may be windmilling and look good, create no significant power.

The installation itself needs considerable power to operate its blade configuration and other services. Winds can vary over a three to one speed range very readily, and in that scenario the produced power will vary in the ratio of 27 to one. This highlights the reason why backup supplies are an essential part of the supply chain.

In order to alleviate the problem, would it not be a good idea if wind power generator suppliers provide a supply chain producing a steady and controlled power level? With the advent of very high capacity batteries or supercapacitors with fast charge capability, these sources of power might direct their varying quota into a battery storage pack. Constant power levels could then be delivered to the grid from the battery according to the average power fed into the battery system. A better measure of the useful power delivery from wind turbines might then emerge.

One might visualise a stack of thousands of batteries - storage as big as a conventional power station - fitted with suitable fail-safe properties, which would be power suppliers of the future. Indeed, if batteries were used as a main distributor of power, every source could direct its power into storage. We could then see generators of any variety operating at optimum efficient output day and night.

G D Cutler MIET, by email

Flawed or not?

Your report on the 'Fatally Flawed' campaign to ban the use of safety covers for electrical sockets (Analysis, Vol 4, #5) was interesting. While the idea of a specification for anything designed to fit in a 240V socket seems a good idea, I do not agree that covers should be outlawed completely.

Once again engineers seem to be spending time looking for the perfect solution. This device has been proven to protect children from risk; I know families who use them with children who have an unusual fascination for sockets and leads, and it stops the behaviour.

It's true the device can be used in an unsafe manner, but so can the plugs on the end of any cable. What we must remember is that very few novel and practical ideas can guarantee total safety, but certainly can prevent some, if not many, accidents.

Improve the specification but don't ban something that the general public tells us is a good idea.

As an engineer, my first question for an issue like this would be: "how many people has this safety device saved and has it introduced a new safety risk that wasn't there before?"

Mark Ward CEng MIET, Norwich

Many years ago, a well known manufacturer of electrical accessories brought out a BS 1363 socket outlet with an interlocking system that required equal pressure to be inserted on each pin simultaneously to cause the shutters to open, preventing deliberate overriding of the shutter mechanism. These sockets, in effect, do away with the need for any other protective measure.

The real issue here is that specifiers should not be selecting 'normal' BS 1363 socket outlets, and that as part of their 'designers' duties' should be carrying out a risk assessment of not only where the sockets are to be installed, but, perhaps more importantly, who is likely to have access to them. It follows that in the domestic environment and in public buildings such as schools there is a significant risk of unauthorised interference justifying any decision to specify accessories by manufacturer and product reference.

One possible problem is that - as far as I am aware - the idea is patented. Public procurement rules can be perceived by some as an obstacle preventing specifiers from selecting products by manufacturer or by product reference but this can be solved by specifying the product generically. Master specification systems such as NBS Engineering Services have facilitated this for a number of years.

W Clark MIET, by email

For some years before retirement I served on IEC sub-committee SC23C, one of whose tasks was to produce a standard for a 16A, 250V AC worldwide plug and socket outlet. We considered the operation method for shutters to live sockets but concluded that shutters to live sockets should be opened by the simultaneous insertion of both live plug pins.

I see no need for the use of plastic covers for socket outlets that are fitted with shutters protecting both socket outlets. At the time of which I speak, the relevant department of the appropriate ministry carried out a historic analysis of injuries due to the misuse of 13A plugs. The majority were due to people standing on plugs which had been left on the floor.

JE Toms FIET, Chester

The purpose of these plug covers is to enhance safety, provided that they are used correctly. Misuse could expose the live terminals and thus create a hazardous situation, but a very similar dangerous condition can arise if an ordinary plug is also misused in a similar manner.

I consider that such covers do enhance safety, because they cover small openings on walls that tempt small children to insert objects in them. They are not easy to remove by small children and it should be the responsibility of the adults in a household environment to store and use these covers correctly.

The campaign's suggestion that "any device intended to plug into a BS1363 socket without the intention of making electrical contact" should be banned from sale should be considered carefully. Such a change may make plugs, adaptors and other pluggable devices in sockets that have a plastic earth connector non-compliant with the standard.

Andreas Kyrou MIET, Epping, Essex

More dangerous than socket covers are some extension flex multiway sockets. One I own has the top of the earth aperture closer to the edge of the box than the space between earth and live apertures, so a plug can be inverted with the earth pin fully inserted leaving the phase pins hanging over the edge.

Christopher Penfold CEng MIET, Salisbury, Wiltshire

Nice little earner

I must disagree with Steve Beeching's viewpoint when he supports the validity of describing television aerials as "digital aerials". In contrast, I support Trading Standards who requested that the word "digital" be removed from his friend's advertising (Letters, Vol 4, #5).

While I am not suggesting that this applies to the case mentioned by Steve, far too many aerial contractors and salespeople exploit the general public's technical ignorance by suggesting that, when upgrading to a digital TV, they automatically need to replace their aerial with a "digital" aerial. In many cases the existing aerial will work perfectly adequately.

It is true that there are instances where what might be adequate for analogue terrestrial TV reception might not prove sufficient for digital TV reception, perhaps where the newly introduced digital service has initially to radiate at a reduced power to minimise interference with contiguous analogue channels until the latter are closed down.

Each installation and location should be assessed on its merits. It is too easy to suggest that "now you've bought your digital TV you need a digital aerial"; albeit a nice little earner for some!

Lynda Lavelle CEng FIET, Goffs Oak, Herts

Colour coordination

A much simpler idea for avoiding patient problems and cutting NHS bills than those proposed in Inventors' Inbox (Vol 4, #5) is to use a colour coding scheme for pills similar to that used on electronic components.

Currently, all pharmaceutical manufacturers use their own colour coding schemes which causes unnecessary confusion for patients, especially those who have to take a 'cocktail' of pills each day. It would not be a problem if patients received pills from the same manufacturer continually, but this is not the case. It is very confusing for many people on the receiving end of this chaos.

Surely it would be possible to agree international standards for pill colouring just as the engineering bodies have achieved with components?

Adrian Wagstaff CEng MIET, St Neots, Cambs

It depends what you're doing

The interview with Prof Richard Wiseman in your 'Happiness Issue' (Vol 4 , # 4) mentions the old chestnut of the glass half full or half empty in respect of positive thinking. I would have thought that, as engineers, we had moved on from this hackneyed riposte of the psychologists and realised that it depends whether you are involved with filling or emptying.

If your control system was designed to effect the rapid evacuation of the pressure vessel, and after the design time had elapsed it was still half full, then one would not very happy, but you could tell the client not to worry because, at least, it was half empty.

Dr Nigel Bennett MIET, Marple Bridge, Cheshire

Rail enquiries

You report (Vol 4, #3) that on the 2 February this year, due to heavy snowfalls, the UK National Rail Enquiries website received 16 times its normal demand but "continued to function, though not all users could get access".

Is that a redefinition of "function"?

Alistair Fox CEng MIET, Expertek, Warwick


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What they're talking about on the Internet

A user of the IET website forums is considering a career change: I've been an electrician for four years and need a change. I'm interested in the electricity distribution network and cable jointing. How would I retrain as a LV cable jointer? How long would it take to become a qualified live jointer? I've seen courses for £6,000 but I don't want to pay all that and not be able to get a job because I don't have experience.

From my experiences in the USA, you need to get a job either with the company who train you or one of their approved contractors. After time in the field they send you to their training centre, then you become certified. We have courses through NECA-approved agencies which only cost about $1,000. Get some on-the-job training before attemping that. Google your local power company, it should list employment opportunities.

The jointers I've spoken to have started with DNOs as trainees and moved up through LV then to MV/HV. With previous electrical experience it may be possible to skip the jointer's mate stage. Your best bet might be to contact local DNOs and see what they have to say; most have training programmes. I wouldn't suggest going on a course then applying for work as I suspect you're right about your lack of experience. 

Contact specialist companies like Prysmian, a major cable manufacturer and service company offering HV cable jointing services. The larger electrical contractors also frequently have their own jointers up to 33kV. With modern XLPE-type cables, the training required is much shorter than with paper/lead-type cables, and this is potentially a growth area with the number of wind farms we're going to need to install in the very near future, with most (if not all) using XLPE cables, at 11kV and (mostly) 33kV.

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