Allowable earth resistance limits 1

[AKassem]

Dear All ,

1) What is the maximum acceptable earth (ground) resistance for intrinsically safe IS instruments
and for non intrinsically safe instruments NIS??

2) what is the maximum earth resistance for grounding a PLC and DCS sytems according to standards ?
as i know that for other electrical equipment (panel body , motors , junction boxes ,... ) the limit is around 5 ohm

can any body refer to IEC or IEEE standards for these values ?
Thank you for your help

 

[zappedagain]

IEC 60079 (and the many subparts) define the Explosive Atmosphere requirements for Europe, and thus define Instrinsic Safety requirements. A quick scan through the subset of documents that I have shows in 60079-14 Section 12.2.4 that anything less than 0.2 Megohm is considered earthed from an electrostatic discharge point of view. The same section shows that a TN-S system needs a earth ground path that is less than 1.0 ohm at a safety barrier.

Your local electrical codes can put another spin on this. You need to figure out which codes are applicable. There is a lot of subtlety to this question. That's probably why no one has responded yet.

Z