Grounding and Bonding - Industrial

[scrub12]

In addition to the EGC being ran with branch circuits to panels and loads downstream of service entrance equipment - I've often seen supplemental bonding to building steel or ground in addition to the EGC ran with the branch circuits. Is this supplemental ground required by NEC? In other words, do panels and motors specifically need an additional ground conductor connected to the building grounding system in addition to the EGC run with the branch circuit? I've also seen MCC's bonded together. Is this a code requirement or just a supplemental good to do to make sure all conductive material stays at the same potential?

 

[augie47]

Neither is NEC required but seemingly commonplace in some large industrial installations,.

 

[bobby ocampo]

In addition to the EGC being ran with branch circuits to panels and loads downstream of service entrance equipment - I've often seen supplemental bonding to building steel or ground in addition to the EGC ran with the branch circuits. Is this supplemental ground required by NEC? In other words, do panels and motors specifically need an additional ground conductor connected to the building grounding system in addition to the EGC run with the branch circuit? I've also seen MCC's bonded together. Is this a code requirement or just a supplemental good to do to make sure all conductive material stays at the same potential?

Supplemental bonding is based on equivalent impedance of two parallel conductors. Kirchhoff's current law of parallel conductors.

 

[don_resqcapt19]

It is a practice left over from when most industrial systems were ungrounded systems. There is no code or technical reason to provide the extra grounding paths.

 

[scrub12]

It is a practice left over from when most industrial systems were ungrounded systems. There is no code or technical reason to provide the extra grounding paths.

Thanks. Would it be a code violation since it provides a parallel path for ground fault current back to source?

 

[don_resqcapt19]

Thanks. Would it be a code violation since it provides a parallel path for ground fault current back to source?

Parallel equipment grounding paths are not a code violation.

 

[infinity]

Parallel equipment grounding paths are not a code violation.

I agree, with the exception of 250.6 you cannot "over ground" something. Running multiple EGC's, connecting to the building steel, installing additional ground rods for equipment, all are permitted.

 

[don_resqcapt19]

I agree, with the exception of 250.6 you cannot "over ground" something. Running multiple EGC's, connecting to the building steel, installing additional ground rods for equipment, all are permitted.

The only time 250.6 is an issue is where you have multiple points of connection between the grounded conductor and the EGCs or the earth.

 

[electrofelon]

I did some work on a several megawatt ground mount P V system where in addition to all the wire EGCs to inverters and panelboards, there was a "bonding conductor" that looped around the whole system, run in the cable tray, and tagged onto all the inverters and panelboards. The "designer" clearly dimmed the lights, made sure he was alone and pleasured himself thinking about the "good grounding" he came up with and all the money he was making his client flush right down the toilet. The climax was probably putting the ground rod triad on the drawing.