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Mentor or discussion forum on IET 5th EDITION code of practice

WHERE do I get LEARNING discussion topics and feedback as I would in a classroom format or from a college mentor on many QUESTIONS I have regarding 5th EDITION IET Code of Practice?? 

For example on Page 80 Table 10.6..  1.5 mm cable has a maximum current carrying capacity of 13 Amps.... YET online I am finding PAT engineers testing Industrial extension leads 1.5 mm having 16 Amps run through them and in BLACK cable with BLACK sodding 60309 connectors... EXTREMELY baffelling and not with an axe to grind and as a none electrician am taking the exam soon THINGS are NOT matching up to spec...I need clarification.. I need answers to many seemingly oddball stuff..

Another quick on:   Page 98-99  5th Edition IET..  If you want peeps to get confused this is it:  ES1 is equivalent to Class III ok... then ELV and SELV (no PELV and no FELV??) are WHAT.. class II? 

An exam Q will TRY an TRIP me up over Low Voltage and Extra Low Volts ok.. seemingly obvious YET online sources declare 0-1000 volts AC and 0-1500 volts DC as Low Volts yet another no no no its 120-1500 DC and 50-1000 AC

IF i take that second reference at FACE value on page 99 in the IET we see a table declaring ES2 at 120 volts DC 50 AC  what is that doiing sat right in the MIDDLE of that table??  and what is ES2?  its not clear and I am in mind

to class ES2 as CLASS II...... furthermore in SELV we see a sodding CP being available as basic protection in some cases?????????  Getting really strapped over this guys..

Parents
  • Well, speaking personally, some of these I can advise,  on but note I do not teach this nor do I have any input into the docs themselves so do not shoot the messenger please.
    what books are you looking at ?

    Lets hit a few,

    1) Cable ratings are not hard and fast, as it depends how the cable will be used. The rating is really the current at which the copper core gets hot enough that it may in the long term damage the plastic of the insulation. A cable coiled or in a place that is already warm like a boiler room will not be able to safely carry as much current as the same cable spread out or just in a cooler place.  You will see different ratings for the same cable published, and always look for the test conditions (BS7671 seems to liek 30 degrees ambient but ungrouped as the base case, then de-rating with hotter settings, or up-rating when it is cooler, and of course reducing the rating when grouped.  Other national standards assume similar but not identical things, and as far as I can tell the IET does not always assume the same thing in all its publications either ....)
    In the UK it is almost never 30C so the BS7671 ratings can often be pushed a bit in practice.

    2) I presume by 60309 connectors you mean the 16A ones that can under certain situations be pushed ot 20A. Nothing stopping you fitting a thinner flex if you know the load is never going to be the full 16A (is it just used for lighting perhaps) or if it is fully loaded but the load is only on for a few mins at a time so the cable has no time to heat up  - as an example your kettle at home may well be 3000watts (12 amps say) on 0.75mm2 flex - but its fine because by the time the cable is getting hot the kettle has pinged off.

    3) ES1, ES2 ES3 MS1 MS2 MS3  do  not map to the ADS types 0, 0A, 1,2 etc

    The ES series are energy limits are more useful for deciding what precautions to take when deciding how skilled folk need to be to be operating  kit wit with the lid off, MS are mechanical hazard ratings for things that are heavy or have other risks,  like entrapment or  rotating parts inside.


    The ADS types are just that  types  of ADS, of which only class 1 and class 2 are common in the UK, but sometimes you will see things that are a mixture so the rack is class 1 but the kit in it is class 2 for example.
    Class 3 is for things that run on ELV,

    Note the UK uses the IEC voltage  levels.Avoid those of other countries, yes the web  is a confusing place.

    EC voltage range     AC RMS  (V)          DC voltage (V)        Defining risk
    High voltage                  > 1 000               > 1 500                 Electrical arcing
    Low voltage            50 to 1 000               120 to 1 500         Electrical shock
    Extra-low voltage     < 50                      < 120                     Low risk
    Though folk often forget the risk of  fire from higher  currents at ELV.

    Mike.

Reply
  • Well, speaking personally, some of these I can advise,  on but note I do not teach this nor do I have any input into the docs themselves so do not shoot the messenger please.
    what books are you looking at ?

    Lets hit a few,

    1) Cable ratings are not hard and fast, as it depends how the cable will be used. The rating is really the current at which the copper core gets hot enough that it may in the long term damage the plastic of the insulation. A cable coiled or in a place that is already warm like a boiler room will not be able to safely carry as much current as the same cable spread out or just in a cooler place.  You will see different ratings for the same cable published, and always look for the test conditions (BS7671 seems to liek 30 degrees ambient but ungrouped as the base case, then de-rating with hotter settings, or up-rating when it is cooler, and of course reducing the rating when grouped.  Other national standards assume similar but not identical things, and as far as I can tell the IET does not always assume the same thing in all its publications either ....)
    In the UK it is almost never 30C so the BS7671 ratings can often be pushed a bit in practice.

    2) I presume by 60309 connectors you mean the 16A ones that can under certain situations be pushed ot 20A. Nothing stopping you fitting a thinner flex if you know the load is never going to be the full 16A (is it just used for lighting perhaps) or if it is fully loaded but the load is only on for a few mins at a time so the cable has no time to heat up  - as an example your kettle at home may well be 3000watts (12 amps say) on 0.75mm2 flex - but its fine because by the time the cable is getting hot the kettle has pinged off.

    3) ES1, ES2 ES3 MS1 MS2 MS3  do  not map to the ADS types 0, 0A, 1,2 etc

    The ES series are energy limits are more useful for deciding what precautions to take when deciding how skilled folk need to be to be operating  kit wit with the lid off, MS are mechanical hazard ratings for things that are heavy or have other risks,  like entrapment or  rotating parts inside.


    The ADS types are just that  types  of ADS, of which only class 1 and class 2 are common in the UK, but sometimes you will see things that are a mixture so the rack is class 1 but the kit in it is class 2 for example.
    Class 3 is for things that run on ELV,

    Note the UK uses the IEC voltage  levels.Avoid those of other countries, yes the web  is a confusing place.

    EC voltage range     AC RMS  (V)          DC voltage (V)        Defining risk
    High voltage                  > 1 000               > 1 500                 Electrical arcing
    Low voltage            50 to 1 000               120 to 1 500         Electrical shock
    Extra-low voltage     < 50                      < 120                     Low risk
    Though folk often forget the risk of  fire from higher  currents at ELV.

    Mike.

Children
  • Touch Currents..run at something like 0.1-0.5 mA up to 2mA according to book... is this this like a sensation on the fingers and why does ES2 have 

    5-25mA since this is Let Go range or going into it ? 

    The ES classifications are about power available so I am thinking It would be better for me to understand and easily recognize them by Watts as only new equipment will bear the labeling is there typically a range of kit like DJ or HiFi and IT that fall into ES1 and or ES2 ?

    Washing Machines, Dryers, Fridges and Freezers I am imagining will be possibly depending on size or power rating fall into the 4 categories on page 99 as SELV ELV ES1 and ES2 with ES3 being Industrial applications?

    Above all that am I worrying too much ?   

    You mentioned Racks possibly being Class 1 but the kit being Class 2 ... how come... is it Power distribution?

  • much less than half a mA most folk don't feel at 50Hz, though by around 1 mA most people can feel  a tingle and some report pain. By about 10mA it is very painful, and most of us have lost some muscle control. By 30mA, if the current path includes the chest, there is a serious risk of disrupting the heart if the current persists for more than about half a heartbeat period - hence the disconnection time curves have a kink in at about 200-500msec. The touch current for any one appliance is set at the 'irritating tingle' sort of level for most folk, and will kill no-one.

    Mike