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  1. #46
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    Quote Originally Posted by Chas View Post
    Could you please provide a reference for this oft-quoted statement? My copy of AS/NZ 3018-2001 'Electrical Installations - Domestic Installations' has on p62 a Table 6-1 "Guidance on the number of points per final subcircuit" which clearly sets out the circuit conditions for one, two, or three 15A socket outlets per circuit. For a common 2.5mm2 wired circuit protected by a 20A circuit breaker, two 15A outlets are allowed except when the wiring is completely surrounded by thermal insulation -Item(I). Three 15A outlets are permitted on a 25A circuit with the wire gauge dependant on the installation method used.

    Chas.
    When I access the SAI global website I find that AS/NZS 3018:2001 has in fact been withdrawn and according to its history tab I find

    Obsolescent 2009-09-14
    Amendment 1 see DR 02592 CP First published as AS/NZS 3018:1997.
    Second edition 2001

    The intent of this product was to distill out of AS/NZS 3000 all that was needed to do domestic wiring with it being obsolete I suppose it is back to finding your way through the 611 pages of AS/NZS 3000:2018.

    If you look at table C9 p483 of AZ/NZS 3000:2018 You can see that the contribution of a 15A socket outlet is 12A when a 2.5mm^2 wired circuit is protected by a 20A breaker and since 2 x 12A = 24A is greater than 20A you cannot have two 15A outlets on that circuit.

  2. #47
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    Quote Originally Posted by lamestllama View Post
    The NZ argument is certainly not a straw man and I am surprised with your interest in electrical safety you are not already aware of the meticulous statistics kept by the Electrical Regulatory Authorities Council?

    You can find the latest at http://www.erac.gov.au/images/downlo...02017-2018.pdf

    For the last few years NZ has certainly had less deaths people per capita by reason of electrocution see Graphs 1.2 and 1.6 of the above document. To say "it's a safer proposition to have it within the scope of a professional" is clearly difficult to justify when the data collected by the regulatory authorities indicates otherwise. Perhaps if we had more decisions based on evidence we might see even better outcomes?
    Very interesting insight, thanks for sharing. Particularly graph 1.6 showing the AUS/NZ breakdown per capita. The results for the past few years are supportive, however we can also view the results prior to that (2003-2009) where the results were opposite to your observation, notwithstanding the outlier in 2005). NZ does have a steeper regression line in the reducing number of deaths than Australia, so there is merit that something there is working.
    One note in favor of neither side of the discussion is that overall, the sample size is not huge... so the swings and roundabouts of a death here or there can markedly change the figures. You can actually see how the NZ outlier of 1.0 deaths per million people in the 2005 sample brought about the crossover point in the line of regression.


    As they say, there are lies, damn lies, and statistics, so here is what I'm picking out of it, which does challenge your analysis, but you are welcome to read it as you may, and your mileage may vary.


    Some points of interest that I found:

    The overview of electrical deaths in AUS and NZ combined:
    40% of electrical deaths occurred in the workplace, compared to 60% in a non workplace setting. (Graph 1.8). Over this same sample period (2017-2018, graph 1.7), 20% were electrical workers (those licensed to do electrical work), 20% were workers, who were not licensed (ie on the job at the time of death), and the majority, 60%, were the general public.
    Ie the majority of deaths were people not licensed, and not in a workplace at the time of death. Were they doing their own electrical work at the time? Were they renovating and put the sawz-all thru the mains cable? I guess the next level of data may shed some further light on this. Lack of education or knowledge increases the risk of death.
    Looking more broadly, the same trend is seen in the combines AUS/NZ data set in graph 1.9, where the general public and non electrical worker deaths constitute greater than 50% of deaths from 2000-2017, so the trend is valid over the years.

    In plain English, the risks are higher when you are not trained. Is this the call to action for better education? Maybe. Is it worth putting the multi-billion dollar training investment through schools? Is it worth the losses (read decimation) of a whole industry of tradespeople, sacrificed for the 20 or so deaths that we see per year?
    ...I'm no economist, but there is some morbid bastard out there who is crunching the data and knows the cost of these 20 lives, and sadly, it is less than the roll-out of an alternative.


    The data- narrowed to Consumer installations (In the home):
    Section 3 of the report shows fatalities involving consumer installations and equipment.
    "Consumer installation" as per the document, is defined as the installation past the point of supply on the consumer side. ie what the home gamers may be working on- home wiring, changing GPO's, putting circular saws thru conductors etc.
    Of this consumer installation, generally speaking, 'general public' deaths outnumber those of electrical professionals 2:1. (Refer graph 3.1). Is this indicative of the ignorance of the dangers in the home setting?
    Within the consumer installation sub-set, once again (see graph 3.2), 2/3 (67%) of deaths are of a non-workplace nature. The remaining 1/3 would include electrical workers working on consumer installations (ie, fitting a new circuit, excavating on site, renovating etc). Once again, still a greater risk as a layman / general public member. There is the argument that consumer installations have a higher presence on non-workers - ie it's a home, not a workplace- but I think that goes without saying.
    The most interesting part of it, for me at least, is Graph 3.3- showing that 67% of deaths occur as a result of misuse or interfering with equipment or wiring- as an example the thread title of 'modifying a power plug' on a welder for example.

  3. #48
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    Quote Originally Posted by Commander_Keen View Post
    Of this consumer installation, generally speaking, 'general public' deaths outnumber those of electrical professionals 2:1. (Refer graph 3.1). Is this indicative of the ignorance of the dangers in the home setting?
    I doubt it. It more likely reflects the fact that there are many times more ‘general public’ than electrical professionals.
    Chris

  4. #49
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by jack620 View Post
    I doubt it. It more likely reflects the fact that there are many times more ‘general public’ than electrical professionals.
    OHS authorities don't usually look at things this way.
    They look at total deaths because that's what hits the news.

    The other thing that should be taken into account is "exposure hours to task".
    A good example of this is the somewhat blinkered focus on total motor vehicle deaths per annum, eg for a State, versus a more real statistic of "motor vehicle deaths per km drive" which has fallen dramatically due mainly to the improvements in motor vehicles.

    The average DIY electrical exposure is going to be in the hours per year category compared to an electrical pro who might be on say 20 hours per week (1000 hours/yr) of direct exposure. If they had the same "exposure hours to task" as pros the numbers of DIY electrocutions would rise dramatically.

    Studies of pro V DIY accident rates are very interesting.
    In most machinery and tool related injuries there's not a lot of difference in accident rates per head per hour of exposure for even as something as simple as a chisel injury. There is a reduction is accident rates with age (as complete idiots will remove themselves from the cohort) but not as much as we might expect.

    My take on this goes something like this.

    The average DIY operator is guided by a mixture of ignorance (ie lack of training and experience), over hesitancy due to under confidence, and non-OHS DIY worplace ie fewer restrictions on how they can do things. The younger they they are the more bullet proof they believe themselves to be so tend to have less hesitancy offset to some degree by quicker reflexes. As DIYers age their hesitancy increases but so does over confidence and reflex time, while ignorance may not change.

    The average pro should be trained (although sometimes I do wonder about this) have a suitable level of confidence, and operates in a OHS workplace restricted space. The older pros get one would assume they should approach a near zero accident rate but unfortunately they can also get too overconfident and more casual, and of course have slower reflexes. This is why even experienced pro operators still injure themselves and have accident rates that are higher than might be expected.

    All this goes to show that, whether you are a DIY or a PRO you can never be too careful.

  5. #50
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    Quote Originally Posted by BobL View Post
    The average DIY electrical exposure is going to be in the hours per year category compared to an electrical pro who might be on say 20 hours per week (1000 hours/yr) of direct exposure. If they had the same "exposure hours to task" as pros the numbers of DIY electrocutions would rise dramatically.

    Studies of pro V DIY accident rates are very interesting.
    In most machinery and tool related injuries there's not a lot of difference in accident rates per head per hour of exposure for even as something as simple as a chisel injury. There is a reduction is accident rates with age (as complete idiots will remove themselves from the cohort) but not as much as we might expect.
    You are attributing all of the "general public" deaths to the "DIY electrician" category which I believe is a totally incorrect interpretation of the results.

    These are just non-electricians (members of the general public) who get electrocuted - the definition of how and why they got electrocuted is unknown, but I would guess the bulk of the deaths would NOT be attributed to "DIY electrical work".

    The hours of exposure is pretty irrelevant, as you can get electrocuted pretty much anywhere - we are constantly surrounded by electrical appliances, electrical wiring, overhead power lines, etc.
    Cheers.

    Vernon.
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  6. #51
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Vernonv View Post
    You are attributing all of the "general public" deaths to the "DIY electrician" category which I believe is a totally incorrect interpretation of the results.
    These are just non-electricians (members of the general public) who get electrocuted - the definition of how and why they got electrocuted is unknown, but I would guess the bulk of the deaths would NOT be attributed to "DIY electrical work".
    I never mentioned general public deaths I only was referring to DIYers who die directly while doing electrical work - these are know quantities. General public deaths arising from DIY electrical work or indirectly from things like house fires resulting from DIY electrical work is less well known but just makes the numbers worse

    The hours of exposure is pretty irrelevant, as you can get electrocuted pretty much anywhere - we are constantly surrounded by electrical appliances, electrical wiring, overhead power lines, etc.
    By hours of exposure I am referring only to hours spent working on electrical work.
    If we let the average DIYer perform 40 hours a week of electrical work for a year how long do you think they would last compared to a qualified sparky.

  7. #52
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    Quote Originally Posted by BobL View Post
    I never mentioned general public deaths I only was referring to DIYers who die directly while doing electrical work - these are know quantities.
    Where? From the stats linked in this thread??? ... I must have missed them.

    Also you were replying to a quote regarding "general public" deaths.
    Cheers.

    Vernon.
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  8. #53
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    Default Maybe, maybe not

    Quote Originally Posted by [FONT=Lato
    [/FONT]If you look at table C9 p483 of AZ/NZS 3000:2018 You can see that the contribution of a 15A socket outlet is 12A when a 2.5mm^2 wired circuit is protected by a 20A breaker and since 2 x 12A = 24A is greater than 20A you cannot have two 15A outlets on that circuit.
    So this could be correct. It could be incorrect. I don't have a copy of the AS3000 in front of me. In many cases maximum demand calculations also come into play. Basically maximum demand allows for the fact that it is unlikely that all equipment on a circuit will be turned on and running and the same time. Thus while the first 15A GPO is rated at 12A, the second 15A GPO might only be rated at 6A for a total of 18 Amps. While a maximum emand calculation is all well and good a sparky on his game should also be asking the property owner if the two appliances connected to the two 15A GPOs are going to be run at the same time, and wire the circuit appropriately.

    Having had a few days to gather my thoughts (that's a slow process!) on the original topic I think that a look at some history might be revealing.

    Once upon a time there were only fuses for protecting electrical circuits. The fact that they have been phased out in favour of circuit breakers for domestic use tells you that maybe they only did a so so job. Two obvious problems with fuses.

    1. Can't tell an earth fault from a phase to neutral short circuit and thus have to be rated for full circuit load.

    2. Often able to hold current well beyond their rating for long periods of time.

    Neither of these characteristics make them particularly safe. As an example of point 2. I witnessed a ground mount substation go up in flames because a 400 amp fuse was later found to be holding 495 amps of load for several hours a day. The heat generated was enough to cause the 400 amp rated switchpanel to go up in flames. A rather unplanned for event in a CBD carpark!

    Now referring that back to our 10A vs 15A plugsand sockets

    Flexible cables traditionally came in three ratings 7.5 Amps, 10 Amps & 15 Amps. Historically the cost of materials was a very major part of the installation cost as compared to today. I can offer the post above where a 50kW supply has been run to a shed (Way to go my man, high fives there etc.). 40 years ago that would not have happenned because the cost of the cables would have been such a large part of the total. It still would be expensive today however the labour costs are a much higher percentage of the overall job. This, back in the day, meant that circuits were usually only wired in the minimum sized cable required to do the job, a 10 amp rated cable for a 10 amp rated circuit. The consequences of plugging in a 15 amp rated appliance to such a circuit might be quite unpleasant given it was protected by fuses with the two issues listed above and given that the fuse wire could be upgraded by any layman to prevent "nuisance blowing" to say a lump of number 8 fencing wire! What could possibly go wrong???

    The simplist way to to prevent someone plugging in a 15 amp rated appliance to a 10 amp rated socket would be to make it physically impossible to fit them together i.e. a larger earth pin. Today we would call that an "engineering" control measure.

    Fast forward to the present day, cable insulation has a higher temperature rating, we understand a bit more about what happens if you run cables through thermal insulation or bunch them together or run them in conduit or in parallel. We use circuit breakers with built in RCDs, so the question really becomes, is it ok to bypass an engineering control that may have outlived it's usefulness?

    I'm going to say no. For two reasons.

    Firstly, still plenty of 10 amp circuits run in unknown conductors protected by fuses loaded, supposedly, with 10 amp wire.

    Secondly, there is a risk, more likely with untrained laymen, of getting the polarity wrong and then failing to adequately test it afterwards. If the active and neutral are reversed then any earthed metal on an appliance may be at 240v. Plug such an appliance into a circuit protected by fuses and you have a death waiting to happen. I also would not guarantee an RCD to protect you, they fail and due to a lack on inspection it often goes unnoticed.

    Interesting that in all the replies to this thread, this point has not been made as it is a far greater risk than starting a fire.


    To sum up, If you don't have an inspection routine for your RCDs, if you don't know about polarity and how to use a megger for continuity testing, if you don't have the specific equipment required for adequate testing, then probably you should leave your 15 amp plug tops alone.


    Disclaimer I'm a sparky. Sometimes I'm not on my game, sometimes I have three left feet all made of clay, the above is my opinion and constitues general advice only, do not rely on it, your life and the lives of your loved ones may be at risk, no reponsibilty accepted.


    Cheers

    The Beryl Bloke
    Equipment er.... Projects I own

    Lathes - Sherline 4410 CNC
    Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.

  9. #54
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    Quote Originally Posted by Theberylbloke View Post
    If the active and neutral are reversed then any earthed metal on an appliance may be at 240v.
    I don't quite understand this - there is no N-E connection inside earthed appliances. If there was, the RCD would always trip.

    Or do you mean swapping active and earth?

  10. #55
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    Quote Originally Posted by Theberylbloke View Post
    So this could be correct. It could be incorrect. I don't have a copy of the AS3000 in front of me.
    Well I do have a copy of AS3000:2018 in front of me and what I wrote is a correct report on the contents of table C9 of AS/NZS 3000:2018 and applies when the outlets are intended for general use . For instances where it could be more or less restrictive all you need do is look at note 9 to table C9.

    IMG_20190120_205021.jpg


    You said you had a few days to gather your thoughts. Why not check the only source that actually matters AS/NZS 3000:2018 in that time?

  11. #56
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    Quote Originally Posted by Commander_Keen View Post
    Very interesting insight, thanks for sharing..
    You analysis is flawed on the basis of the definition of what an electrical worker is. In NZ a person who is not an electrician but is doing electrical work he is legally allowed to do is an electrical worker.

    As always definitions are important in anything to do with statistics.

  12. #57
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by RustyArc View Post
    I don't quite understand this - there is no N-E connection inside earthed appliances. If there was, the RCD would always trip.

    Or do you mean swapping active and earth?
    Yep - I've seen a few.
    One was beside bakelite GPO in a bedroom that probably only ever had been used to power a couple of bedside lamps and when the new homeowner plugged a small AC unit into it .......
    Another was a DIY effort in a lean to laundry. Someone had brought power from a lighting circuit in the house roof cavity to the laundry and wired a single bakelite 3 pin socket and a separate switch to it. No earth wire installed either.
    Seen a few home made extension cords with the A-N swapped and E-N swapped as well.
    A recent fave was an HD expander board I found during rubbish pickup - probably fell off a truck. Someone had replaced the 3 pin with a 2 pin plug AND connected the A-N the wrong way around.
    I haven't seen many since the newer white plastic electrical fittings with colour coded dots on the terminals have been around.

  13. #58
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    Quote Originally Posted by Theberylbloke View Post
    I can offer the post above where a 50kW supply has been run to a shed (Way to go my man, high fives there etc.).
    That was me and I detect some sarcasm, although I'm not offended. Actually I think my super-sizing is sensible.... it cost maybe $1000 to upsize the cable (50m of cable was about $2k) and now my options are open. The house has a 63kVA supply. The shed is quite big too (the previous owner used to keep 3 school buses in it). If I see an ex-industrial machine with a 20kW motor or a 50kW induction furnace then it would only cost me a few hundred to connect them, and I'd likely get them cheap because few others in the hobby would have the power supply. Better than re-digging a 40+ metre trench!

    I no longer let electricians make sizing decisions because in my experience they aren't good at it. By that I mean they tend to aim for the minimum required and not allow for later upgrades. An example was a few years ago I put in a swimming pool heat pump and the electrical work was around $4500. The heater worked OK although needed to run through the night in winter. Two years later I put in a 10kW solar system and it made sense to upsize the heater so it could do the job in daylight hours while the electricity was essentially free. The electrician returns and tells me the cable is not large enough, and that he is unable to pull a bigger one through the conduit so it would be a totally new trench etc at X thousand (I don't recall the amount). And I was thinking wouldn't it have been sensible to have oversized the original cable... isn't it obvious?

  14. #59
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    Quote Originally Posted by Pumpkinate View Post
    And I was thinking wouldn't it have been sensible to have oversized the original cable... isn't it obvious?
    I guess in the never ending race to win jobs by quoting cheaper than the opposition it isn't always obvious.

  15. #60
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    When I built my house, I opted for 3 phase supply, (only $200 extra because somebody stuffed the quote up I think), initially a 25kVa transformer was installed, but then they saw some of the gear I had and upsized it to a 50kVa. Now I wish I had more as I acquired a 100CFM screw compressor that could draw 63Aof 3 phase!
    Anyway, when the house was wired in by a qualified sparkie, he had to ring his mate as he had no idea how the set up the 3 phase bore pump and pressure switch. I really do wonder how good many sparkies are given the big mistakes I've seen over a period of time. It really seems that core knowledge is lacking and complacency is rife.

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