You can no longer post new replies to this discussion. If you have a question you can start a new discussion
The maximum permissible disconnection time is 0.4 s in TN system. Why and from where this value (0.4 s) is obtained?
Former Community Member
The maximum permissible disconnection time in in the event of a short circuit between a phase conductor and a body or protective conductor or a protective-neutral conductor is 0.4 s in TN system. Does anybody know this value (0.4 s) obtains from where? How this value is obtained?
For 5 seconds, it is as good as 'forever' in terms of being many cycles of heartbeat, you need the current to be below 30mA - which should be seen as the upper limit for 'probably survivable' certainly not enjoyable.
At 30mA, actualy rather below, muscles spasm, and you can expect bruising internal and external from the muscle movement. The body can take more at higher frequencies, but it needs to be carefully controlled. Equally, with a current path that does not include the torso, you can survive considerably greater currents, so long as heart and head are avoided.
The two viable ways to reduce the current to a value ssafe for linger exposure are either to increase the resistance (Johns matting, or in my lab world, a waxed wooden floor or linoleum, or when out in the field rubber soled boots..), or to ensure that both ends of the human being are at more or less the same voltage, live or not (the point of equipotential bonding.)
The RCD does not limit the current - the supply voltage and and the body conspire do that. The RCD can only limit the time of exposure, hopefully to a duration short enough that even if the current is over 100mA you have a reasonably good chance of surviving. Without an RCD, you can add burning, cooking and higher risk of death to the symptoms as above.
Testing a 30mA RCD at 5 times In, is not enough to be truly sure of this.
For 5 seconds, it is as good as 'forever' in terms of being many cycles of heartbeat, you need the current to be below 30mA - which should be seen as the upper limit for 'probably survivable' certainly not enjoyable.
At 30mA, actualy rather below, muscles spasm, and you can expect bruising internal and external from the muscle movement. The body can take more at higher frequencies, but it needs to be carefully controlled. Equally, with a current path that does not include the torso, you can survive considerably greater currents, so long as heart and head are avoided.
The two viable ways to reduce the current to a value ssafe for linger exposure are either to increase the resistance (Johns matting, or in my lab world, a waxed wooden floor or linoleum, or when out in the field rubber soled boots..), or to ensure that both ends of the human being are at more or less the same voltage, live or not (the point of equipotential bonding.)
The RCD does not limit the current - the supply voltage and and the body conspire do that. The RCD can only limit the time of exposure, hopefully to a duration short enough that even if the current is over 100mA you have a reasonably good chance of surviving. Without an RCD, you can add burning, cooking and higher risk of death to the symptoms as above.
Testing a 30mA RCD at 5 times In, is not enough to be truly sure of this.
