Instrument Earth Bar and Safety Earth Bar

@ PWSlack . . . don't the two (clean and dirty) then go to the same earth (even if through separate pits)?

since i often like your answers, i am tempted to ask many questions to you . . . to help demystify some "ground" realities on this subject . . . with assumed permission, i submit . . .

in case there is a direct lightning strike in the vicinity and the EARTH rises to a very high potential . . . then will not both the earths rise almost equally? in such a case what is the use of the isolation of the "clean" earth inside the panel?

why only lightning strike? even in the case of a direct flashover from line to earth at a near to source point of low impedance, may a similar risk be perceived?

if the two earth are indeed to be isolated then should the instrument earth have a resistance built in series? to limit the current?

if the instrument aux supply is derived from the same source as the panel power supply without any isolation transformer in between then does having a separate earth bus bring any advantage? or disadvantage?

I give you a GA, not because you provide a good answer, but because of the good questions you raise!

I'm a graying mechanical engineer and have often seen "clean" ground and "dirty" grounds in communications shelters. I have not completely understood why and have just accepted the practice.

This post supplies several great replies that have given me a better background to understand why. But like sobefatehi, I am curious how the clean and dirty grounds are kept "separate", even though they both are ultimately have only 5 or 10 ohms resistance between them?

And to the poster who mentioned putting an impedance on the ground connection, what size and configuration is this coil? (Is it a coil?)

IMO, there is always going to be a Finite amount of impedance differences in any form of grounding or earthing mechanism(s). This holds true for both of the so-called "clean" and "dirty" grounds /earths. Regardless of how well the bondings are made, different ground loops will always exist due to this finite amount of differences in ground impedances. Minimizing ground loops differences will help improve or minimized this ground noises up to a certain acceptable level..

Further to #1, in some labs the instrument earth is connected to its own earth mat or pit or whatever to ensure that it's as "quiet" as possible.

Hi All,

In our Petrochemical plant, Clean earth & Safety Earth install seperately.

Thanks

The answer is correct to an extent and the argument is also correct since the reason for providing separate earthing points in the panel is to allow for separate earthing; they can not be bonded together for any reason. They should be separately earthed. If for any reason they want to communicate or shake hands, it must be through a ground impedance.