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VOLTAGE OPERATED ELCB BE842

Former Community Member
Former Community Member
Regarding voltage ELCB's BS842 I am currently looking at replacing an old Wylex fuse board with a new C.U with individual rcbo's system is TT. Question is if I remove the earth connections from this device can it be used as the isolator switch for the new CU?

  • Dare I ask...


    What's the advantage in removing the earth wires from the ELCB?
  • well it may reduce the risk of it tripping during thundersorms, or faults on adjacent properties.
  • I have seen it done a fair few times, but haven't done it myself.


    Andy B.
  • Former Community Member
    0 Former Community Member
    Basically the elcb is to be removed as its type Bs842 no longer confirms to regulations. I am removing the old wylex fuse board and replacing it with a new CU with individual rcbo's. My question was rather than remove the obsolete elcb could I use it as an isolator switch
  • What is the resistance of your earth rod? With six 30mA RCBOs and no overall RCD, your worst case leakage before anything trips could be as much as 180mA. That give you a max permissible earth rod resistance of 277 ohms to keep the touch voltage below 50V under normal circumstances. Ideally, you will want it much less than that. 


    Regards,


    Alan.
  • StuartBa:

    Basically the elcb is to be removed as its type Bs842 no longer confirms to regulations. I am removing the old wylex fuse board and replacing it with a new CU with individual rcbo's. My question was rather than remove the obsolete elcb could I use it as an isolator switch 


    BS 842 is not listed in Table 537.4, and therefore it's not easy to determine whether the device complies with Regulation Group 537.2 in the 18th Edition. One particular issue is that BS 842 doesn't explicitly state that the device is suitable for isolation, but this could perhaps be inferred by other wording in the standard, and it requiring the ELCB also complies with other product standards that may be suitable for isolation (but also are not listed in the current 18th Edition for that purpose).


    However, I do know that a BS 824 device is only specified for prospective fault currents of 3 kA (if working to the standard - although I guess a particular manufacturer may have chosen a higher rating). If the supply has been upgraded from its original demand in the past, or will be in the future, that rating could be exceeded. (See ENA Engineering Recommendation P25 for further information - it's common these days, to simplify designs and purchasing requirements consumer units and associated equipment, to assume single-phase installations up to 100 A might be subject to 16 kA prospective short circuit currents.)


  • Former Community Member
    0 Former Community Member
    Alan l havent measured that yet the job l discuss is not yet started. Im just asking people's advise. In stead of installing an isolator switch im proposing that I fit a time delayed RCD. Thank you for your comments.
  • You have no choice, it has to be an up front time delay rcd. Unless the DNO provide an earth facility.


    Regards, UKPNZap