Disconnection Times

[securespark]

OK. So you have shown that a TD (S type) RCD will comply because it will disconnect within 200ms.

Back to my original question then...

How can a G type RCD on a TT supply comply if the standard for them is 300ms?

 

[dingbat]

OK. So you have shown that a TD (S type) RCD will comply because it will disconnect within 200ms.

Back to my original question then...

How can a G type RCD on a TT supply comply if the standard for them is 300ms?

First, these are two different standards; the disconnection time required for circuits and the performance requirements of the RCD. It's up to you to meet the disconnection time. How do you do it? Easy:

Keep your Zs at a value which will trip your RCD within the required time. If you take the maximum acceptable RA (or Zs) as 200 Ohms, you'll get over an amp of earth fault current, which, even on a 500mA RCD, should meet a time of 150ms (table 3A, Appendix 3)

 

[Spark123]

As Dingbat says, as long as the current is significantly higher (or as it was worded 2x) then 200mS is achievable.
I can't think of any general type RCDs I have tested recently that don't trip at their rated current exceeding 200mS tbh.

 

[securespark]

Fair enough. Thanks guys.

 

[securespark]

I remember Securespark? on about compiling a TT readings guide quite a while ago

Could you jog my memory? I can't remember that...