Reg 419.2 Applicable to VSD driven motor?

Good afternoon,

When using cable design software such as ElectricalOM, there is a check box within the "Earthing" tab / adiabatic check of CPC. It states Provision of  regs 419.2 & 419.3 are applicable. (BS7671)

If checked it will remove the warning regarding the earth fault / disconnection time (should a warning exist with the modelled install)

Can someone confirm with a degree of certainty that the checkbox would reg 419.2 be applicable to a motor supplied from a VSD drive? 

  • No, I don't think so because the VSD would be part of the machine rather than the fixed installation.

  • Probably correct ... although there might be some layouts where the wiring between the VSD and motor would fall back into BS 7671's scope.

    If it did, then data from the VSD manufacturer is probably the way to go. I many cases I would have thought that the impedances involved would mean that the to produce a voltage difference exceeding 50V into a short(ish) circuit, the VSD would have to produce such a large current that either it would shut down promptly to protect itself or it would go phut and let all the magic smoke escape, so achieving ADS in a rather one-off if roundabout manner.

    Or if there is any doubt, apply supplementary bonding (419.3 option).

       - Andy.

  • Can you give an example of where 419.2 is applicable then please? i.e where power electronic converters are part of the fixed installation? I am struggling to think of another.

    You see, I would argue given the fact I have designed, modelled and specified the VSD as well as its settings. Also modelled the cabling from the output to the motor and and the input cabling (if its a stand alone VSD in field)  it would be very much part of the fixed installation. Its not like you can just plug one into to a socket is it?

    And here lies the problem with BS7671 these days. fairly intelligent people can't interpret the regs correctly. I am sure I understood the majority of the 16th Ed back when I was wet behind the ears. Now more than 25 years later with loads more experience, I struggle like hell. Mainly because you have to read about 30 regs before you can understand the first one you were looking at. Put it this way I won't be buying the next edition. total waste of money IMO.

  • Can you give an example of where 419.2 is applicable then please? i.e where power electronic converters are part of the fixed installation? I am struggling to think of another.

    UPS systems? Inverter generators?

       - Andy.

  • Ah yes. UPS, perfect example. So why would you consider a UPS part of fixed install and not VSD inverter?

  • So why would you consider a UPS part of fixed install and not VSD inverter?

    "Fixed installation" is a bit outdated as a description of what BS 7671 covers - these days it's more like everything (fixed or otherwise) that isn't covered by more specific standards. Very often a motor + VSD would form part of an overall "machine" and so be covered by something more specific - like BS EN 60204. But an installation powered by a UPS doesn't have its own standard.

        - Andy.

  • Or if there is any doubt, apply supplementary bonding (419.3 option).

    419.3 is not an option because 419.3 starts by stating "except where reg 419.2 applies" 

    I thought  reg 419.2  had been written with VSD drives in mind (albeit very vaguely) as they have in built fault protection, which by my limited knowledge the electronics would disconnect the output within with the required disconnection time. 

  • Fair enough I'll be more specific and rephrase the original question to hopefully get clarification, as I am not taking about a washing machine or simular.

    Question: When using cable design software such as ElectricalOM, there is a check box within the "Earthing" tab / adiabatic check of CPC. It states Provision of  regs 419.2 & 419.3 are applicable. (BS7671)

    If checked it will remove the warning regarding the earth fault / relating to disconnection time (should a warning exist with the modelled install)

    Can someone confirm with a degree of certainty that the checkbox relating to 419.2 be applicable to a standalone 3 phase induction motor, on a water treatment plant or other industrial setting. Where the motor is either:

    A) Directly connected to the output of a wall mounted VSD drive (not in an assembly) via SWA cabling 

    B) Directly connected to the output of a VSD drive mounted within a pump starter (Form 4 MCC assembly) via SWA cabling 

  • A) Directly connected to the output of a wall mounted VSD drive (not in an assembly) via SWA cabling

    I have to admit that it did occur to me that you could have, let's say, a VSD mounted to the wall (or on a stand on the floor, or even screwed to the ceiling) supplying a fan. Equally well, as you say, a pump.

    Back to the OP, I have no doubt that design software is very helpful when it comes to cable calculations and so on, but it will never tell you which box to tick else it would have done it for you.

  • never tell you which box to tick else it would have done it for you.

    No need to be patronising Chris. I was not asking if I should tick the box or not.

    I was seeking clarification of reg 419.2 and in what situation to apply it to. I know exactly what the check box does. If ticked the software does not report where a circuit has not met the required max disconnection time.

    The question has not arose from a design I am working on FYI. I came across an Amtech report from a past contract a few years back done a someone else and noticed that there is a comment on the report stating "

    Auto dissconnection time has been exempted as equipment complies with BS7671 419.2Protection is provided by the

    VSD

    This report would have been based on one of the senario B I have given. So are you saying they are incorrect by adding this comment?