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Best practices

MrJack96

Hi all can someone please give me some advice on the following? 

 

  1. say you’re maintaining a circuit and you realise parts of the circuits do not comply to the regulations what is the standard procedure for example ZS values that do not comply or IR that’s too low. I know in the industrial setting we are pressured to keep things going (critical kit) but say even if we’ve got it in writing we’ve said it’s potentially dangerous and we’ve been told in writing to switch it back on who is then at fault?

 

  1. say the circuit is an old installation and complied at the time of installation if we were then doing work on that circuit say for instance changing adding a spur to sockets that aren’t RCD protected what is the protocol with regards to bringing it up to current standard? 

 

Parents
  • 0

    where is additional resistance in the fault path under fault conditions,  will not the fault current be reduced and the disconnection time seriously lengthened?

    Oh yes ..(Churchill insurance voice). But the voltage at point of fault, already set by the R1R2 voltage division, probably to about 100-150 v if live cores and CPC have similar cross-sections will then be further reduced as the voltage divider is now R1 + R_fault dividing against R2. If you can get the exposed voltage  below 50V the rules of the game suggest you can safely  lengthen the ADS operation time to ‘never’ without danger to life.

    In reality I'd be very nervous about getting close to that lower limit, especially with things like  pump repairs, where wet hands could mean the body to metal contact may be lower resistance  than expected, and a lower threshold, e.g. 25V would be safer than 50.

      Equally, exposing a dangerous voltage for 5 seconds, or even ten is fine if no one is there when the fault comes on. If they are then the 5 secs of the regs  is not really adequate protection anyway, and earth fault relays RCDs etc are our weapons of choice.

    Mike

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  • 0

    where is additional resistance in the fault path under fault conditions,  will not the fault current be reduced and the disconnection time seriously lengthened?

    Oh yes ..(Churchill insurance voice). But the voltage at point of fault, already set by the R1R2 voltage division, probably to about 100-150 v if live cores and CPC have similar cross-sections will then be further reduced as the voltage divider is now R1 + R_fault dividing against R2. If you can get the exposed voltage  below 50V the rules of the game suggest you can safely  lengthen the ADS operation time to ‘never’ without danger to life.

    In reality I'd be very nervous about getting close to that lower limit, especially with things like  pump repairs, where wet hands could mean the body to metal contact may be lower resistance  than expected, and a lower threshold, e.g. 25V would be safer than 50.

      Equally, exposing a dangerous voltage for 5 seconds, or even ten is fine if no one is there when the fault comes on. If they are then the 5 secs of the regs  is not really adequate protection anyway, and earth fault relays RCDs etc are our weapons of choice.

    Mike

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