Draft for Public Comment - IET Open combined protective and neutral (PEN) conductor detection devices (OPDDs)

The IET's new Standard (IET 01) includes definitions, requirements and tests for open PEN detection devices (OPDDs) and is now open for public comment, find out more here https://electrical.theiet.org/get-involved/consultations/iet-open-combined-protective-and-neutral-pen-conductor-detection-devices-opdds

Deadline for comments: Friday 2 February 2024.

  • I've been perusing this draft - there are a few things which puzzle me - just wondering if it was considered appropriate to discuss the details here (so I could refine/correct my comments before submission - saving the committee having the trawl through some of my dross) or whether the technical details need to remain out of the (unregistered) public domain?

      - Andy.

  • That's difficult without knowing the context of the queries ... PM me and I'll see if I can help.

  • Thanks Graham - you've got mail!

  • Thanks Graham - you've got mail!

    You too !

  • Cheers Graham. That certainly helped!

       - Andy.

  • Note that this is a draft for public comment. and anyone can download it here by leaving a name and email address.  You do not need to be an IET member, or logged in to do so. The Email can be a burner if you are paranoid.

    However the copy so downloaded is only yours, and may not be further reproduced, except fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988

    So, as with many similar documents, providing we are reviewing it or criticizing it.but not reproducing great chunks of it, we are fine to discuss the contents, and arguably to do  so will lead to a more complete set of review comments.

    Here are my areas of suggested improvement. I do realise this is very much a work in progress, and my comments/observations  are intended to provoke debate to lead to a better final, not offend.

    First a general observation.

    1) That some sort of standard is being developed for PEN fault detection is an excellent step forward and to be applauded - for a while we have had the slightly unusual situation that a potentially safety critical device is called up in a standard, but there is no ' and it shall perform like this' requirement to refer to.

    2) I am unclear who this document is aimed at - in parts it reads as if it is solely for manufacturers of such devices - some clearly are, e.g. requirements  like terminal labeling etc, and yet the testing proposed seems to be a mixture of production sample factory tests, (IK and EMC tests, glow wire tests, are destructive, or can be, and tested units would not normally be allowed into the supply chain) and other things that would normally be verified on each device, perhaps in factory, or for programmable / configurable devices at installation time and others that probably should to be a part of periodic tests ( i.e. repeated during an EICR in "sparks speak" ).

    Perhaps (as I suspect it really is a bit of both) it would benefit from a foreword or two explaining which requirements are which.  Then, in a few places the definitions and the language used in parts would do well to better match the  language of their respective audiences. Electronics equipment designers are not usually sparks as well, and while the physics is the same, the rules of the game inside equipment are not the same as outside, where things are a lot less well under the designer's control, and the meta-language to describe what is happening is also different.

    3) Definitions (part of the above comment) the device specific stuff is mostly good but I suggest the following to be at odds with normal electronics use of the same words, and liable to cause confusion.

    " Pulsating direct current Current of pulsating wave form which assumes, in each period of the rated power frequency, the value 0 or a value not exceeding 0.006 A DC during one single interval of time, expressed in angular measure, of at least 150 deg"

    In the pulse power world, a DC pulse is simply one where the direction of current flow never reverses.   (the magnitude may  fall to zero (or for all intents and purposes zero), or rise to any arbitrary value, but the key thing that makes it pulsed DC, is no current reversal...)

    What is being described here however is rectified and chopped mains derived waveforms, not a general pulsed DC. And if we mean less than 60mA at the highest point in the cycle, as opposed to the RMS (or do we elsewhere it implies we might ?) then it should say so.

    "Current delay angle Time, expressed in angular measure, by which the starting instant of current< conduction is delayed by phase control."

    I  assume we mean the no of mains cycle degrees or radians delay, relative to the rising zero crossing of the voltage waveform, or perhaps relative to where the current zero-crossing  would have been had there not been 'phase control',  or as I suspect is mean, conduction angle or duty cycle control...

    4) Factory Test or in service re-test limits are not spec limits.

    A device picked off the production line will not trip every time a ramping supply reaches 262.200000 RMS . It will trip within some tolerance of this. (say between 260 and 265, for an equal balance of failures on either side false alarms and missed dangerous events, or perhaps between 255 and 262.5 if the latter is intended as a limit that may never be exceeded, so that we err on the side of the false alarm)

    It would be better if the voltage spec was written in a way that  acknowledged this reality.

    5) A thought about the supplies waveforms of the future. Around line 2012 in the draft it considers power factors for short circuit tests - I presume the low PFCs for high PSSC are assumed to be inductive (i.e. the current waveform is related to the voltage by phase offset but would if sustained, be a sine wave.) I can see how a reduction in R and the predominance of L can be  related to moving up the street main towards a substation transformer, but considering the greater incidence of inverter derived mains, is this a wise assumption for the future ? Note also that in many areas with a lot of solar farms, at certain times of day the mains voltage as supplied  has become quite noticeably trapezoidal, rather than sinewave I suspect this is  a trend that will continue.

    Personally I have nothing against "Acme thread" waveforms rather than traditional sines - they are easier on the rectifiers in terms of a lower and  flatter peak current after all, but we probably need to include them in our consideration,  as substations with intelligent inverters to push energy from lightly loaded phases into more heavily loaded ones will likely become more common, as the electronics is already cheaper than a second transformer..

    However it affects both power factor (which is a mix of phase shift an non-sinusoidal distortion) and the detection thresholds - as most fast methods are really a peak detector with a degree of integration - true RMS can be done, but is either slow if analogue, or involves waveform digitization and a calculation. More common is a 'near enough' RMS that works for near sine-waves and is progressively more inaccurate as the waveform is distorted.

    Anyway this is getting a bit war and peace, and that was not the intention. Comments/flames etc awaited with interest.


  • fine to discuss the contents, and arguably to do  so will lead to a more complete set of review comments.

    I cant disagree with that (indeed that was behind my initial reply) - I just had it in the back of my head that the distribution process in this case was slightly different from conventional "publishing" -  even if the trust levels are more like a 'gentleman's handshake' than 'two forms of photo ID'.

    That some sort of standard is being developed for PEN fault detection is an excellent step forward

    +1 for that! I'm in two minds though whether it should be an equipment standard in its own right, or merely additional requirements that should be read as supplementing existing standards (e.g. BS EN 61851 if it's built into a charge points or BS EN 60947-4-1 if added to something like a stand-alone contactor) - at the moment it seems to be attempting to be a bit of both, which seems to be adding an awful lot of bulk, but not a great deal of clarity.

    Pulsating direct current

    That definition caught my eye too - it seemed very odd to have 6mA limits built into the very definition of a quantity - rather than as a later requirement. I also noticed that the definitions around Earth Fault Currents were quite at odds with normal conventions (or BS 7671's version of the definitions at least) - especially that in a TN system earth fault currents don't actually have to flow through the general mass of the Earth at all. I've have to re-read the main body of the text to see if they're used to mean something different in this context.

    I did wonder if, given the introduction of appendix 17 of BS 7671, some recommendation regarding power consumption might be useful - given that these devices are likely eventually o be rolled out by the million, every 1W of unnecessary consumption by these devices will add MW of load to the national grid.

       - Andy.

  • ah yes 6mA not 60 well spotted. Still an odd definition, RMS or instantaneous peak I wonder?

    I do prefer either the tens or hundreds of the nearest smaller unit  or exponential notation (so many (units or tens of) mA, or 6E-3 A rather than decimal and zeros 0,0xxx)  as  mis reading is harder - especially when there are more than one leading zero. But then I also prefer  nine-uh rather than 'nine' over the phone to avoid confusion with 'no' or 'null'.

    There is a similar reason that on diagrams and parts lists electronics chaps commonly use the multiplier letters in the decimal point position - so  1k2 is equivalent to 1.2 k ohms, or 1200 ohms, but never normally written as   0.0012 Megs  (and 4M7 is 4million 7 hundred thousand,  8n2 is 8200pF etc

    Interesting idea about the idle power - and often overlooked for things needing an  internet connection which is often assumed to be free,

    For example power draw is now biting BT with their roll-out of domestic  fibre to the premises kit, which does not have a low power state to drop back to when the mains fails, making battery back up for power cuts for more than an hour or so uneconomically awkward. (so they do not bother to mention it ) 

    I reckon half the houses in the UK have an ADSL router taking 10-15 watts all the time to connect to the exchange over copper and to radiate WiFi broadcast packets, even when everyone is in bed, just on the off chance a packet arrives. That's a lot of Mw given the no of houses in the UK.

    To be truly 'green' there needs to be both a power limit for the kit, and a network traffic limit to save power elsewhere. In many ways, 'nega-watts' the power saved by unplugging something, are hard to beat.


  • ah yes 6mA not 60 well spotted. Still an odd definition, RMS or instantaneous peak I wonder?

    I suspect (and it's still just a suspicion) that it's linked with the 6mA DC limit for A-type RCDs (and RDC-DDs if one has been incorporated into the EVSE) - so all bets are off if it's subject to a decent DC fault current for instance. If so it still feels to me it should be a functional requirement (or limitation on a requirement) rather than part of the definition of a quantity.

       - Andy.

  • I agree entirely - the definition of the phrase just need to clarify the peak value or some sort of time-average, and that although the current is varying with time, there is no reversal of direction, and then the test spec needs to say 'shall operate with more (or less) than a level of X or Y measured in the manner defined above'  as suits the situation.

    And as you say the large DC fault case needs to be handled separately for those odd cases where it is actually a credible failure mode.