Connecting PE to IE 1

[farale]

dear all,

We have three types of earthing systems in our project: protection (power) earth, instrument (clean) earth, and lightning protection earth.

Usually we provide separate earth pits for each type. Earth pits for PE are connected to eaxh other, but not connected to earth pits of clean earth.

I know that they must be finally connected to each other. But how and where?

If possible please point to relevant standards.

Thanks.

 

[dpc]

What is your location? Different standards in different parts of the world. In the US, all of these grounding systems must be bonded together per the National Electrical Code. The "clean" or "quiet" ground for instrumentation was popular in the US decades ago but has been discredited for quite a while - and it is unsafe. Lightning protection system grounds must be bonded to the normal system ground for safety.

Cheers,

Dave

 

[farale]

Dear Dave,

Our project is based on IEC.

I usually add a lot of earth pits throughout the site. Then I make a ring around all buildings and tall structures by adding earth pits around them and connecting them together. Some earth pits shall be exactly below down conductors for lightning rods. All earth pits will be connected to the same grid. This way, we have just one earth grid for PE and lightning.

At last we add a few separate earth pits far from power equipment and PE earth pits. This new set of pits will be used as clean earth.

The question is: how to connect this instrument earth grid to the PE/lightning earth grid? Just in one point? In many points? Directly? Using a chock? Using a nonlinear resistor?...

Thank you

 

[che12345]

Dear Mr farale

Based on IEC, the relevant document is IEC 60364-5-54 Selection and erection of electrical equipment-earthing arrangements.
Reference IEC 60364-5-54 Annex B (informative) [not part of the standard] illustrates the connection of various items to the main earthing terminal (main earthing busbar).
Q1. The question is: how to connect this instrument earth grid to the PE/lightning earth grid? Just in one point? In many points? Directly?
A1. All electrical equipment earthing/bonding are to be connected to the main earthing busbar, which is connected to the power board structure. This main busbar e.g. A is connected the earthing electrode. All instrument earthing conductors may be terminated on an [insulated] busbar e.g. B. A separate conductor connecting B to A. Lightning down conductors shall be connected to the main earthing busbar A and (to the LPS earth electrode if necessary). All the various earthing pits shall be connected to the main busbar A. The aim is [to achieve one point] (only) from the main busbar A to the earthing electrode.

Q2. Using a chock? Using a nonlinear resistor?...
A2. No chock, no nonlinear resistor, no fuse/breaker and no switch (except testing link)
etc. is allowed along the earthing conductor, in order to maintain/achieve lowest impedance especially due to high frequency by lightning etc.

Che Kuan Yau (Singapore)

 

[jghrist]

The important thing technically is that the systems are connected together at only one point. This prevents lighting current from flowing through the other earth systems and prevents harmonics from the PE system from flowing through the clean earth system.