Control.com - Nerds in Control

Dear Friends,

Can any expert of grounding explain in detail that whether the ground/earth for Electrical Power system and Electronic and Control system should be separate or same, and why?

What are the IEC standards related to that issue?

I always keep them seperate, if you have a high fault current flow through the power earth, the voltage rise could damage electronic equipment. If the load is reactive higher voltage spikes and harmonics can be even more damaging to electronics.

earth is earth. they all connect together at some point.

What do you mean by separate, two separate pits for safety and logic grounds? I have read somewhere that these should be separate but also connected to a single point, during whole installation.

Where should I connect my -24V DC?

Hi dear,

What is your control system architecture?
It is likely depend on it!

It is honeywell EPKS with 03 controllers and 04 PLC's. All field signals are coming in C/R and terminating in marshalling cabinets. There is also a hardwired panel which receive data from PLC's.

Some workstations and printers etc, you know the usuals of C/R.

For field instrument power supplies, all 24 V DC power supplies have a common (-24 VDC) connected together, and this common is connected to instrumet/logic ground.

kkk

In Instrumentation, we generally have 2 types of earth pits installed. One pit is called Shield Earth Pit while the other is called Power earth.

While you are designing a big Instrumentation based process control system, we generally have the following equipment.

1. Drives Panels
2. System Cabinets - with PLC/DCS IO cards, RIOs, etc. (Analog IO cards)
3. Power Distribution Panels
4. Digital Panels (Digital IOs)

So we have to separate drive panel grounding as the panel contains heavy noise/harmonics. Secondly, we have to consider ONE redundant shield Earth Pit & ONE redundant Power Earth Pit. This way, we can ensure that even earthing is redundant and this eliminates chances of earth failure.

Power Earth Pit contains earthing from bulk power supplies, Controller Power Supplies, Panel Earthing, Panel Door Earthing, etc.

Shield earth Pit contains earthing from Analog IO shielding cables, Analog signal isolators/safety barriers, etc.

Hope I am right.

Sastry MRKS