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Termination of coaxial bonding cables for link boxes 1

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qman5

qman5

Electrical
Sep 10, 2012
28
Hello all,

Per IEEE 575 (Sec. 7.5.2 Bonding leads) coaxial (concentric) bonding leads are recommended for distances greater than 10m to reduce the surge impedance.

I'm having trouble understanding the application of this recommendation. Some link boxes are manufactured for these concentric bonding conductors with apparent means to terminate the outer concentric wires to. See attached image.

bonding-lead-3_tk3o3a.jpg


I understand that the inner bonding conductor is connected to the screen of the cable and the SVL or grounding point, but what about the outer concentric conductor? Is this bonded to the case ground of the link box and left open on the side of the cable screen? Or how would the outer concentric conductor be connected on the side of the cable screen?

I would appreciate if someone has some insight to this.

Thanks,

qman5
 
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The concentric earth cables are used when you have an electrical discontinuity in the screen/sheath across a straight joint, for example at the end of a minor section in a cross bonded installation. The inner conductor connects to the screen on one side of the joint, the outer conductor to the screen on the other side of the joint. The cross bonding of the sheaths is achieved in the link box. You might also use the concentric cables at a mid point link box on a single point boded installation.

Regards
Marmite
 
 http://files.engineering.com/getfile.aspx?folder=cc148b1b-5904-4094-858d-551e47f9cbca&file=Capture.PNG
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Thanks, this makes more sense to me now. My confusion stems from the fact that the standard doesn't seem to distinguish between a single run or minor sections.

I then question if single core cables can be used for 3 phase link boxes when the distances between terminations is greater than 3 meters?

As a safe option, I have decided to go with 3 single phase link boxes to keep the lead lengths as short as possible, however, I'm wondering if this is still recommended or even needed?
 
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