Safety switches are sensitive to control tones

I am writing this letter of warning to your publication since any approach to bureaucratic "black holes" would be a waste of time. The best way is to alert people to such problems. This may not be a problem in towns but it is certainly related to rural areas.

As a person from the milliamp side of the electrical/elec­tronic disciplines I have considered the compulsory installation of Safety Switches (core balance relays) as not unreasonable but over the years I have heard rumblings about their nuisance value. There was always reference to some appliances, such as refrigera­tors, causing nuisance tripping. However, people need to take heed of my problem that started about two years ago.

As regular as clockwork, 6:30am in winter and 7:30pm in summer (I live in a daylight saving area), about three weekday mornings every week, the breaker would trip out. Switch back on and no problems. I had no timers set in my house. It did occur on other occasions but the worst time was going away for several days knowing most likely that my freezer would become a hot box. I thought that it might have been a large pump starting in the district but a check of neighbours turned up no similar problems.

I did contact electricians but the general response was that it was an intermittent fault and they were not really interested in spending an inordinate time trying to tie down the fault in a narrow window.

I tried all the usual fault-finding methods. First, check appliances for earth leakage both by direct check of resistance and a high impedance check for capacitive loading by looking for a time constant rise. Then I had the tedious effort of isolating one distribution circuit before isolating individual loads over time, bearing in mind the 2-5 minute window to observe the ef­fect. Just when I thought I was getting somewhere, the other circuit goes off. It did cross my mind that the problem was possibly the breaker itself. No, these are made to Australian Standards and therefore they work or they die. How wrong I was.

A chance meeting with a rural-based electrician, a chance comment and the gist of his response was "It’s your Safety Switch. Replace it. I have had several go that way. Even some new replacements have had the problem. It is a problem related to off-peak control tones. I know of several cases in the surround­ing district".

A new Safety Switch (not Clipsal) solved the problem. This suggests that there is either a deficiency in the Standard, failure to maintain standards or a design fault. How widespread this problem is I am not sure but it is a situation that is less than satisfactory.

Perhaps the sensing circuit has some unwanted capacitance that, coupled with the sensing coil inductance, creates a paral­lel tuned circuit at or near the control tone’s frequency that pushes the sense output over the trip limit.

A simple addition to the Standard, if it does not include such a requirement, would require the sensing circuit to be positively desensitised to the tones used for off-peak power control. If this requirement exists then the Standard is not being achieved. Either the Standard needs revision to include such a requirement or the standard needs to be enforced.

Being cynical, at almost $100 a pop there is no incentive for manufacturers to strictly comply since the consumer has to get a replacement. The only problem with this attitude is it creates an attitude to safety devices that they are treated with scorn and derision by being just a nuisance.

Brendan Falvey,
Gundaroo. NSW.

What about a valve amplifier?

As a regular reader who has not missed reading one of your magazines I would like to comment as follows. I buy your magazine for enjoyment and interest. The two articles I always enjoy reading are the Serviceman and Vintage Radio.

Yes, I have built some of your transistorised projects but I also like working with valve equipment, even if it is old tech­nology. No different to collecting and working on vintage cars; people do it for enjoyment. What’s wrong with restoring old radios and bringing them back to life, especially in today’s throwaway society?

I remember the first time I read your statement that SILI­CON CHIP would not publish a valve amplifier design. To me the statement had a sense of arrogance. In other words, if people weren’t interested in the latest technology then don’t read SILICON CHIP.

But what about the people who simply enjoy valve technology? I would be interested to know how many people would be interested in building a high quality valve amplifier just for fun and enjoyment.

Michael Justin,
via email.

Help wanted on army receiver

I am seeking details on a piece of disposals equipment. It is a 5-band WWV receiver made by Beckman, model No 905WWW. It was used by the Australian Army with a DSN number of 6625-66-012-7046. I suspect the vintage to be 1963. The device is rack-mounting and has miniature tubes with crystal-locking for each channel. Any help would be appreciated.

Craig Cook,
Melbourne, Vic.
(03) 9890 2117 (AH)
email: craigc@melbpc.org.au

AM Stereo is still alive in Australia

I was surprised to recently learn of one of Australia’s closely guarded secrets, that many commercial AM radio stations and probably one ABC station (4QR) broadcast in stereo. Those in Melbourne are Magic 693, Sport 927 (3UZ), 3AW 1278, 3MP 1377 (temporarily in mono) and 3AK 1116. There are undoubtedly others in the other states.

The stations themselves do not publicise this fact, possi­bly because stereo AM receivers are not normally available (although decoders may be added to some existing radios). This is also strange because the additional cost of incorporating AM stereo features into an AM/FM stereo radio at the time of manu­facture would be minimal, one would expect.

www.amstereoradio.com will provide information to anyone interested in following up this matter. There is also an active discussion/lobby group on http://www.egroups.com/group/iaaas-amstereo.

Alex Brown,
via email.

Comment: we published an AM Stereo radio in September, October & November 1989. We had the impression that AM Stereo was dead, despite the fact the stations may still be using the gear.

More on New Zealand’s electrical regulations

Further to my previous letters, I spent almost the whole of March in New Zealand and I had a very informative and productive meeting with a senior official of the Energy Safety Service within the Ministry of Economic Development. Here is a brief summary of some of the things I discovered.

(1). In a comparative study of international annual electrical fatality statistics done by the New Zealand Energy Safety Serv­ice, Queensland consistently had the highest levels of electrical fatalities in Australia. Much more interestingly, Australia had higher levels of electrical fatalities than any other country studied, with the exception of Northern Ireland.

This New Zealand study confirmed the results of a similar study done by the German government, so the results are corrobo­rated. The country with the lowest electrical fatalities (by a huge margin, varying from year to year between 0.5 and less than 0.1 deaths per million of population), is The Netherlands, and this is one of the many countries that allow householder DIY wiring). Australia has the second highest levels of annual elec­trical fatalities (varying between 2.5 and 4 deaths per million of population).

Now Northern Ireland is an extremely turbulent society. Yet by the German and New Zealand comparative studies, Northern Ireland is the only country with higher levels of electrical fatalities than Australia! The Australian statistics reflect the gross irresponsibility of the great Aussie tradition of allowing powerful vested interest groups to "regulate" themselves.

(2). Prior to 1992, it was illegal for any electrician in New Zealand to explain any technical aspect of electrical wiring to anyone who was not a trainee electrician, or not otherwise li­censed to do "electrical work". This prohibition was seen as a serious impediment to the new electrical safety regime and was eliminated in the 1992 changes to the NZ electrical safety re­gime. (It appears there is no similar prohibition in the current Queensland legislation).

(3). Anyone can assist an electrician to do electrical work in New Zealand, without the electrician having to look over that person’s shoulder. So for instance, after an electrician has agreed to supervise your work, you could bolt up the control panel and connect the house cables to it on your own and the electrician would just do a quick check on your work when it is finished.

(4). Only completely new work and extensions, etc, are required to be inspected in New Zealand. You can replace and relocate wiring, power points, switches, etc, without notifying the au­thorities as long as cable lengths are not altered. The exception is wiring in metal conduit. New Zealanders are not allowed to work on systems run through the old metal conduit systems. Howev­er, they can remove all the metal conduit and then rewire the house with modern cable and components.

(5). Interestingly, the overwhelming majority of additions to houses in New Zealand are done on an owner-builder basis, there­fore much of New Zealand DIY electrical work is the wiring asso­ciated with such additions. Of course, entire houses are built by owner-builders in New Zealand and in these cases almost all the wiring is done by the owner.

(6). Specially certified "inspectors" do all required inspec­tions, not ordinary electricians. The "inspectors" are liable for the quality of the inspection but not for the quality of the work. If and when the work appears to be particularly shoddy or unsafe the inspector can refuse to do the inspection.

New Zealanders are advised by their Energy Safety Service to secure the services of an "inspector" before they begin their DIY electrical installation work. These "inspectors" are private operators, not government employees, and of course, the homeowner has to pay for the inspection service. These inspectors advise the homeowner on the technical aspects of the installation if they feel such advice is needed.

(7). The senior NZ Energy Safety Service official I spoke to made it clear to me that homeowner DIY wiring will not change in New Zealand as a result of all the ongoing reviews, which are now largely concerned with the health and safety of electrical work­ers in industry. The attitude of the New Zealand authorities is that there is no danger whatsoever when DIY electrical work is done according to law.

(8). The New Zealand Energy Safety Service has the attitude that old cables, switches, power points and other fittings need to be able to be replaced at low cost. They believe the sorts of dan­gerous situations where people continue to use cable and fittings of questionable serviceability are dramatically reduced by allow­ing householders to replace these items themselves.

(9). Before 1992, electrical engineers and associate engineers in NZ were authorized to do all "electrical work". This has now changed for new graduates though all licenses current in 1992 continue. Recently graduated engineers and associate engineers can apply for electrical contractor licenses after fulfilling appropriate (minimal) training.

In Australia, there is no way to avoid the four-year ap­prenticeship. Let’s face it, which electrical contracting busi­ness would take on an adult trainee on adult wages when they can get a teenage apprentice at slave labour rates?

So effectively, there is no practical path to an electrical contractor’s license for engineers and associate engineers in Australia.

(10). When New Zealand decided to reassess its electrical safety regime they sent an official overseas to study the electrical safety regimes in other countries, including the United Kingdom and USA systems. In the National Competition Policy review of electrical safety in Australia, there is no requirement whatsoev­er to even look at "world’s best practice".

(11). In the United Kingdom, electrical licensing is relatively weak and electrical standards compliance is primarily enforced through insurance. The UK, which has long had householder DIY wiring, has annual electrical fatality levels below 1.0 per million of population. Compare that to the Australian figures!

My extensive interactions with New Zealanders were such that I can wholeheartedly confirm the comments of I. Morrison in the January 2001 Mailbag. New Zealand really is a much kinder, fairer society that is much more protective of civil liberties than we are in Australia. So please, wake up Australia!

Otto S. Hoolhorst,
Brisbane, Queensland.

Solar power not bogged in bureaucracy

I write in response to the letter entitled ‘Solar power bogged in bureaucracy’ on page 33 of the December 2000 issue. The Sustainable Energy Industry Association (Aust) Ltd - SEIA (Aust) is working hard to improve the quality, safety and reliability of renewable energy systems designed and installed as grid-connected and standalone power supply systems. In doing so, the Associa­tion works closely with Standards Australia and with the Austra­lian Greenhouse Office (and state Energy Departments).

Under the rebate scheme alluded to in the ‘Solar power bogged’ letter, applicants can receive a rebate ($5 per watt) off the cost of the photovoltaic modules in the system. This is approximately half the cost of the modules and they can save thousands of dollars on the overall cost of their system. It would be folly of any state energy department distributing these amounts of money not to ascertain the bona fides of the system; ie, they must make sure that the number of panels claimed has actually been installed.

This, unfortunately has already lead to rorts of the rebate system – owners have been claiming rebates for panels which were not supplied or, if supplied, had been taken away after the event. They also need to have some confidence that the system will work – hence the requirement for a load analysis. If the system has been poorly designed and there is no match between the design load and the size of the battery bank, the PV array and the other balance of system components, the reputation of solar as a viable energy source may be harmed.

The system must also be safe! Many people seem to think that extra low voltage DC systems are inherently safe. They are – to the extent that the current and voltage in the cable from the array to the battery bank and from the battery bank to the load will probably not kill anyone. However, incorrect cable sizing can lead to the cable overheating with the result of a possible fire started in the roof space of a house. The ‘dead short’ current of a battery will be in the order of thousands of amperes – shifters vapourise at these currents.

There are significant safety issues and installation to the appropriate Australian Standards should give greater confidence that the system presents no danger. One wonders whether the author of the letter understands AS 4086.2, AS 4509 parts 1, 2 & 3, AS 3000, AS 2676.2, AS 1170.2, AS 2676 parts 1 & 2 and even AS 1768.

The issue of earthing is also raised. Consider a perfectly legitimate MEN earthing system on the AC side of the inverter and an earth on the battery negative. If an earth fault occurs on the AC side, there may be a 240V potential difference between the two earth stakes. A person standing between the two earth stakes could receive a fatal shock! Clearly with only one earth stake the system is inherently safer from this point of view.

Earthing is not a simple issue – in some conditions it may be better to earth and in others it may be better not to. The installers of the AC and DC systems must liaise to determine the most appropriate earthing scheme for the overall system.

Consequently, it is in the interests of consumers, the state energy departments and the industry, to impose the perceived ‘bureaucratic’ requirements.

The ‘invasion of privacy’ is only to the extent that the state energy authority needs to ascertain the design and in­stallation characteristics. The choice is simple – accept the rebate and the associated perception of an invasion of privacy or don’t accept the rebate. Thousands of home owners around the country are quite prepared to have their system audited so that they may receive this generous assistance.

The writer may not be aware that there are considerable losses from a solar system. The specifications of a photovoltaic module stipulate the current, voltage and power ratings under standard test conditions (STC) – one of which is an internal cell temperature of 25°C. The output power of a cell is de-rated at 0.5 % per degree above 25°C. If the ambient temperature is 35°C, the internal cell temperature will be approximately 55°C. This means that the output power is reduced by 15%. On top of this, there are system losses – 85% typical inverter efficiency, 90% typical battery efficiency and up to 5% cable losses. This gives a total loss of 45% – which is quite realistic in many circumstances. The figure mentioned (50%) may be slightly conservative – but not by much.

In any case, the outcome of under-sizing the photovoltaic array will most probably be no lights and no power to run the computer. Any trained system designer will consider all of these losses and work from the load backwards to determine the capacity of the battery bank and photovoltaic array, specifying cable size, balance of system components and array tilt and orientation angles to optimise the performance of the system.

The writer clearly has a system which he is happy with. Others have taken advantage of the rebate scheme to obtain the same satisfaction. If any readers wish to take advantage of the rebate program they should contact their state energy department or the national office of SEIA (Aust) on (02) 6230 1562.

Ray Prowse, Executive Officer,
Standards, Training & Accreditation.
email: Ray.Prowse@seia.com.au