Maximum Disconnection Times

[Cookie]

What is the reasoning behind having a 0.8 disconnection time for up to 120 volts Uo, but it then jumps to 0.4 seconds as soon as you go over it? Wouldn't it be better 0.8 seconds for 150 volts Uo and under, 0.4 seconds 150 volts and over Uo?

 

[davesparks]

Is a low earth impedance necessary on TN-C-S and TN-S?

What exactly did you mean when you asked if it's necessary to test the earth rods on TN systems?
I assumed you meant the earth electrodes at the transformer for the N-E link at source and/or the other TNCS electrodes used along the distributing mains.

 

[Cookie]

What exactly did you mean when you asked if it's necessary to test the earth rods on TN systems?
I assumed you meant the earth electrodes at the transformer for the N-E link at source and/or the other TNCS electrodes used along the distributing mains.

Do you have earth rods at the service on a TN-C-S or TN-S system?

 

[davesparks]

Do you have earth rods at the service on a TN-C-S or TN-S system?

No, the regulations dont require this.

 

[Cookie]

No, the regulations dont require this.

Can I ask why? NEC requires that the service has grounding electrodes. So it is a surprise to hear this.