Grounding Problem in Siemens DCS


Thread Starter


We have a Siemens DCS system SPPA-T 3000 in power plant of 700 mw. In DCS panel grounding connection done separately for signal earth and power earth. Both are connected in daisy chain in the panel and carried to the earthing pit separately.

It is found that resistance measured in the panel vary greatly from 24 ohm to 150 ohm in different panels.

Why is it so? How much resistance between them is considered safe for operation?
Resistance from cabinet instrument ground to ground connection in earthing pit 100-200 milliohms.

Resistance between instrument grounds in your cabinets, 10-20 milliohms.
> resistance between power earth and signal earth is varying from 40 ohm to 120 ohm.

It should not show short condition. But how much resistance is safe for operation? If anyone knows why the above variation? AC noise can disturb the resistance value?
You need to be specific not only with the resistance magnitudes you describe but also how you are measuring it.

Grounding is a detailed design matter.