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ZS for an motor run off an inverter

MrJack96
Hi guys. How can you test the zs of a motor run off an inverter drive?
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    But there is a problem, and that is when the 'appliance' is not self contained.  A cooker is fine, power goes in, raw food goes in, burnt mess comes out. That is what it is supposed to do.  (I prefer to cook on a fire myself but that is a side note and  just a matter of familiarity)

    In the case of the separated motor and the VSD, (or nearer home, the heating system and the circulating pump) it may well be that each installation is very different, and the design authority is the individual who put it in, and  may well not be available for comments. How a committee meeting that is separated from that design and installation in both time and space can claim to know it better is beyond me.


    If the VSD data sheet says it meets IEC 61800-5-1, then you know short circuit protection been considered, or at least whoever printed the data sheet thought it had been.

    But even if not,  so llong as the designer ensures the Earth path to the motor is adequate to avoid a dangerous condition with a dead short to a live conductor,  then any fault where a line shorts to earth at the motor, but then in the VSD a few ohms are added in series with the live core cannot cause a danger either - and that is the only credible fault mechanism.


    You cannot sensibly protect against a person being connected between the motor phases any more than you can if they are connected L-N on a normal circuit.
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    No, a VSD is a stand-alone device, it needs nothing else to operate except a motor. There is no assembly, and one can buy integrated motor-VSD packages which can just be connected or have a plug fitted. As for the GU10 lamp, the product standard is mechanical and says very little about the contents, the electronics, the brightness, the filament or LEDs, the colour temperature, the life. All this is simply about "level playing fields" and interchangeability and stifles innovation. Some standards are useful to all, for example, Screw Threads. However, this does not prevent other threads from being used if they are more suitable for some purpose, although this tends to single-source replacements. Cars are particularly bad at having bolts that are non-standard, particularly in the head size, because this suits automated assembly, but not repairs. BS7671 is becoming very prescriptive about items that really design decisions, usually on the grounds of alleged "safety" improvement, the real question is "exactly what degree of safety and risk" is reasonable and this needs to be exactly defined. If the same were applied to many human endeavors, most sport would never happen because people hurt themselves, some die, transport would be right out.
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    davezawadi (David Stone):

    No, a VSD is a stand-alone device, it needs nothing else to operate except a motor. There is no assembly, and one can buy integrated motor-VSD packages which can just be connected or have a plug fitted.


    That would then be a pluggable appliance and not the sort of thing that we'd have to worry about  as far as BS 7671 is concerned ... the manufacturer would take all responsibility for the essential requirements of the Low Voltage Directive - or in the UK, Electrical Equipment (Safety) Regulations.


    Since the VSD wouldn't do much without a motor, however (the right kind in terms of type and specification for that particular VSD), I'm not really sure it's a stand-alone device?

     



    As for the GU10 lamp, the product standard is mechanical and says very little about the contents, the electronics, the brightness, the filament or LEDs, the colour temperature, the life. All this is simply about "level playing fields" and interchangeability and stifles innovation. Some standards are useful to all, for example, Screw Threads. However, this does not prevent other threads from being used if they are more suitable for some purpose, although this tends to single-source replacements. Cars are particularly bad at having bolts that are non-standard, particularly in the head size, because this suits automated assembly, but not repairs. BS7671 is becoming very prescriptive about items that really design decisions, usually on the grounds of alleged "safety" improvement, the real question is "exactly what degree of safety and risk" is reasonable and this needs to be exactly defined. If the same were applied to many human endeavors, most sport would never happen because people hurt themselves, some die, transport would be right out.




    Today, if the GU10 is mains, the product standards cover electrical safety and efficiency. A filament GU10 is perhaps a different kettle of fish, but those fish are fast swimming away from us. Regardless, the manufacturer is still accountable for the essential requirements of the Low Voltage Directive.


    The difference in this respect between appliances and components is that components either require technical skill and judgement to integrate into a system, or assemble into a pre-manufactured assembly.


    So, yes, pluggable VSD, just go ahead and plug it in ... otherwise, you need the technical skill and judgement. which may well have to rely on some specification or instruction from the manufacturer.

     


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    But, and it is not in BS7671, but it is common (well round here), a VSD with a socket on the output - but very clearly for one motor., really only so the motor can be isolated and seen to be isolated for maintenance of the machine.
  • 0
    Again Mike, I would say that in such a case, the VSD is the end product, although if the VSD is permanently wired, and the socket-outlet rated 32 A or less, BS 7671 would expect that outlet to have an RCD ... which may not be compatible with the protective conductor currents seen with VSDs ...
  • 0
    In practical terms with an unknown VSD or CH control system or solar pump speed controller isn't the simplest solution just to adopt supplementary bonding downstream? R <= 50V/Ia. With industrial motors with a lot of bonded metalwork about you're probably not too far away from achieving the required resistances by default. With domestic CH systems etc with an upstream 30mA RCD or even a 3A fuse you'd likely be fine just replying on the c.p.c.s without any additional bonding conductors. Then it almost doesn't matter what the fault current is - less than Ia then it's safe to touch, Ia or above then it disconnects within an acceptable time.


      - Andy.
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    Yes, application of Regulation 419.3 is feasible, and then the question of a loop impedance disappears.
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    gkenyon:

    Yes, application of Regulation 419.3 is feasible, and then the question of a loop impedance disappears.


    Yes unless you want to argue that the prospective earth fault current should be assessed.


  • 0
    davezawadi (David Stone):

    What about cookers? They fall foul of 131.1, in that they have hot parts which could cause burns.


    I have to say that I thought that DZ had completely flipped here until I read 131.3.1 . "... during normal operation of ... minimal risk of burns ". So now your jobbing sparks has to prevent Mary Berry from burning her wrists when she takes a cake out of the oven! ??


  • 0
    lyledunn:
    gkenyon:

    Yes, application of Regulation 419.3 is feasible, and then the question of a loop impedance disappears.


    Yes unless you want to argue that the prospective earth fault current should be assessed.




    Loop impedance is only required for ADS.


    The prospective fault current is required for a number of things ... ADS, if it applies in a particular arrangement, is only one possibility ...


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