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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 need to be patronising Chris. I was not asking if I should tick the box or not.

    You certainly appeared to be asking whether you should tick the box if you have a motor which is supplied by a VSD.

  • You certainly appeared to be asking whether you should tick the box if you have a motor which is supplied by a VSD.

    Where did I ask if I should tick a box or not? I asked if the check box, or more importantly reg reg 419.2  was applicable to a certain scenario. I can then make a judgment myself if I should or should not tick the box should I need to.

    I also asked if ...

    Can someone confirm with a degree of certainty

    You don't appear to be able to answer this with any degree of certainty at all, so there wasn't much purpose in throwing your 2 pence in the first place. 

  • Can someone confirm with a degree of certainty

    You don't appear to be able to answer this with any degree of certainty at all, so there wasn't much purpose in throwing your 2 pence in the first place. 

    Nobody can with certainty because you didn't give enough information.

    I am still of the opinion that if the VSD is part of a machine, it is outside the scope of BS 7671. If it is separate, only the manufacturers can say.

  • Is the wiring between the VSD and the pump part of the fixed wiring where perhaps the pump or VSD may be change or bridged out  but the wiring not ?
    This will be something that is case specific.

    In general, if you are sure that the VSD is providing the ADS function, then the normal rules as set by upstream breakers etc do not apply to cables that are in effect protected by the VSD. In such a case, by all means set the software to ignore that accordingly, but there is an onus to confirm instead that the internal current limits / trips within  the VSD do actually keep the potential shock hazards to either a low enough voltage, or a short enough duration, to give an equivalent level of safety.  It is not just a case of 'its a VSD - out of scope no thoughts required' .

    Of course the regs are not that clear, but I'm pretty sure  that is the intent.

    Mike.

  • I am in no way as clever as those chaps who have replied already, but thinking of VSDs, there are probably only two ways to supply them;

    1) from inside an MCC supply a long run of cabling to the motor and the VSD is located inside the MCC.

    2) Supplied from a DB by a conventional circuit to a VSD and then supply a motor local to the VSD.

    I'd guess that item 1) is outside the scope of BS7671 and you COULD tick the box

    I'd guess that item 2) is inside the scope of BS7671 and until you get to the VSD, then it is outside the scope of BS7671 and you could tick the box for that bit south of the VSD. 

    South of a VSD the tick box is probably applicable.......although it sounds like this reg 419.2 is aimed at manufacturers of electronically controlled circuitry, rather than electricians?

  • 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? 

    The answer is, it depends on whether the VSD has this functionality.

    If the VSD has the functionality, then the manufacturer's instructions must have specific information (see Regulation 419.2) for that Regulation to be invoked ... so it should be very clear to a specifier or installer.

    It's also important to document whether 419.2 is used for maintenance and periodic verification.

    It states Provision of  regs 419.2 & 419.3 are applicable.

    It is, also, possible for a designer to use Regulation 419.3 knowing nothing about the properties of hte VSD, only the design of a supplementary equipotential bonding system.


    It's therefore possible that the designers of the software thought about 419.3, and then thought "well, it might also be possible the VSD may comply with 419.2 at some point as well", so included both options to "future proof" or "catch all"?