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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? 

 

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  • 0

    0.48 ohms is about 475 amps fault current for a 230V LE voltage at the origin.

    Looking at the bussman curves, that could take upto 8 seconds to blow or be faster than 2.

    So it fails the 5 second limit in the regs. and is not safe for a well earthed person to touch while that fuse is blowing.  Mind you, 5 seconds is also fatal if you touch it while the faut is on but the fuse not yet blown.

    In my mind, a small additional risk.

    I;d also worry about the voltage drop - how much of this is R1, an how much R2 - you may be looking at 30V drop at full load. I presume that the motor takes rather less than 100A once up to speed.

    Mike.

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  • 0

    0.48 ohms is about 475 amps fault current for a 230V LE voltage at the origin.

    Looking at the bussman curves, that could take upto 8 seconds to blow or be faster than 2.

    So it fails the 5 second limit in the regs. and is not safe for a well earthed person to touch while that fuse is blowing.  Mind you, 5 seconds is also fatal if you touch it while the faut is on but the fuse not yet blown.

    In my mind, a small additional risk.

    I;d also worry about the voltage drop - how much of this is R1, an how much R2 - you may be looking at 30V drop at full load. I presume that the motor takes rather less than 100A once up to speed.

    Mike.

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