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#128377 - 02/07/03 08:06 AM Ground Resistance ?
VOLTS Offline

Registered: 06/02/01
Posts: 21
I have to install a static ground indicator for a railcar solvent unloading station. The indicator has an intrinsically safe circuit in it. I have read that I.S circuits need very low ground resistance to work properly. I have heard of a product that is put around the ground rod or grounding system to help lower the resistance to ground. Also has anyone used the clamp on resistance testers from AEMC? I am resposible for the grounding system of a large chemical plant were grounding is VERY important. Would this instrument be wise investment or are there other testers that would be a better choice?

#128378 - 02/08/03 05:13 PM Re: Ground Resistance ?
Scott35 Offline

Broom Pusher and

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Bjarney is really sharp as to Grounding System testers and Chemical additives for fixing R / Z levels.

Simply the goal is to have everything in the "immediate Area" at the same potential - so there will be a very low chance to build up an Electrostatic charge between the car(s) and the pumping apparatus.

Impedance and / or Resistance of the Electrode system may not be a high criteria, whereas an Equipotential Plane may be more important.

Got any Specs???

Scott35 S.E.T.
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128379 - 02/08/03 10:10 PM Re: Ground Resistance ?
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
<GASP! Who? Me?> OK, one needs to understand several aspects of grounding, particularly where hazardous locations are concerned. Intrinsically-safe circuits do not necessarily require a low grounding-electrode resistance, but that would be an engineering call by the indicator producer and covered in installation instructions—which should be carefully understood and followed. The more important considerations are {ground} continuity of all conductive surfaces in the area where the work takes place, to keep potential difference as low as reasonably achievable.

As far as testers, you may want to contact AEMC or Megger sales reps and ask them to demo “fall-of-potential” or “three-point” and clamp-on test sets. They all have their positive characteristics, as well as limitations.

The fill material I’m familiar with is

That’s the short version. Don’t hesitate to follow up with any other questions.

#128380 - 02/20/03 07:47 PM Re: Ground Resistance ?
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Are you referring to field installing intrinsically safe wiring with barriers and/or isolators? Or are you simply using a piece of equipment that is intrinsically safe?
If you are installing your own IS circuitry, tell me what brand of barriers or isolators you are using, and I may be able to offer some help.
As Bjarney said, the low impedance grounding doesn't refer to earth resistance, but a ground path sufficiently low to allow the barrier to operate should a fault occur in the hazardous location. The design of the barrier will dictate how this is accomplished.

[This message has been edited by Redsy (edited 02-20-2003).]


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