High voltage cable sheath bonding

[timm333]

[FONT=.SF UI Text][FONT=.SFUIText]I'm just trying to figure out that why is the ground continuity conductor not required when the metallic sheaths of high voltage cables are cross bonded. The total induced voltage is zero when the sheaths are cross bonded, but how does it relate to the fact that ground continuity conductor is not required? [/FONT][/FONT]
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[FONT=.SF UI Text][FONT=.SFUIText]Also the ground continuity conductor is required when the sheaths of high voltage cables are single point bonded, and the purpose of this conductor is to bring the fault current back to the source. But this conductor is insulated and is connected to the ground only on the two ends of the cables. So if, for examine, there is a fault at the center of the cable, then how will the fault current make its way through the ground continuity conductor? Thanks for help![/FONT][/FONT]

 

[Smart $]

I am not familiar with "ground continuity conductor" and "cross bonding" terminology. You should use NEC terminology here.

 

[GoldDigger]

My guess is that the ground continuity conductor only insures that there is a fault return path from the remote end back to the source if the cable sheath fails or is cut.
Like running an end to end wire EGC inside a raceway. Unless there are splices there is no need to bond at intermediate boxes.

Sent from my XT1585 using Tapatalk

 

[Ingenieur]

This has a good description
https://cdn.selinc.com/assets/Liter...CCables_DT_20160425_Web.pdf?v=20160426-085244

cross bonding
at each 1/3 gnd point the ph gnd is transposed to a different ph AND bonded to gnd
so gnd is continuous end to end

single point
at each 1/3 point only 1 end of the cable shield is gnded ... so not continuous
so a seperate ground continuity cond is run between the shield grounding points to provide continuity

 

[Smart $]

This has a good description
https://cdn.selinc.com/assets/Liter...CCables_DT_20160425_Web.pdf?v=20160426-085244

cross bonding
at each 1/3 gnd point the ph gnd is transposed to a different ph AND bonded to gnd
so gnd is continuous end to end

single point
at each 1/3 point only 1 end of the cable shield is gnded ... so not continuous
so a seperate ground continuity cond is run between the shield grounding points to provide continuity

Thanks for the link. I glanced through the document (mostly just the diagrams ). Learned something new.

However, being basically a Code forum, and OP using the term required, there has to be a binding standard. My first reply was meant to induce confirmation, for as best I can tell, that standard is not the NEC.

 

[Julius Right]

In my opinion, in reply to your question, an explanation could be in :
IEEE Std 575-2014 IEEE Guide for Bonding Shields and Sheaths of Single-Conductor Power Cables Rated 5 kV through 500 kV ch. 6.3.3 Parallel ground continuity conductor.

 

[timm333]

Thanks. So in cross bonding, do we achieve the end to end continuity (of ground) through the soil of the earth?

In single point bonding, both ends of the metallic sheath of the cable are grounded and connected together through a ground continuity conductor. So if a single point bonded cable is 500 m in length, and the fault on metallic sheath occurs at a point which is 400 m from the sending end (source) and 100 m from the receiving end, then will the fault current first travel the 100 m through the soil to reach the receiving end, and from there make its way back to the source through the ground continuity conductor?

 

[Smart $]

Thanks. So in cross bonding, do we achieve the end to end continuity (of ground) through the soil of the earth?

No. Sheaths are cross bonded—A to B, B to C, and C to A—at the joint between each minor section. Continuity is maintained from end to end through sheath sections A1, B2, C3; B1, C2, A3; and C1, A2, B3.

In single point bonding, both ends of the metallic sheath of the cable are grounded and connected together through a ground continuity conductor. So if a single point bonded cable is 500 m in length, and the fault on metallic sheath occurs at a point which is 400 m from the sending end (source) and 100 m from the receiving end, then will the fault current first travel the 100 m through the soil to reach the receiving end, and from there make its way back to the source through the ground continuity conductor?

No. Only one [section] end is bonded. The other end is connected to a sheath voltage limiter, referenced to the ground continuity conductor. Sheath sections are bonded together through the ground continuity conductor. Fault current travels all available paths back to the source at the same time. There is no first and last, just how much. Fault current will mostly travel through the sheath to the source end, through the bonding jumper (if any), then through the ground continuity conductor back to source end. If or when the voltage is high enough for the voltage limiters to go into clamp mode, then you get another path to the ground continuity conductor.