how to equipotential long cable ladder

[eliahud79]

i design now a 800 meters long service tunnel
along the tunnel i design steel cable ladder with few cables, the biggest cable for transfer 200 ampers.
beside the cable i design bare copper conductor connected to the ladder every 20 meters for equipotential of the ladder.
is it accepted practice?
is there connection between the crosss section of this equipotential conductor to the nominal current of the power cables or the expected short circuit of the cables.

 

[waross]

In the Canadian Electrical Code, the size of the grounding conductor depends on the size of the largest breaker ahead of the cables and is listed in the appropriate table. Sorry, I don't have my code with me.

Bill
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"Why not the best?"
Jimmy Carter

 

[7anoter4]

The steel cable tray itself could be a grounding conductor according to NEC. In order to assure this the cable tray has to be of a minimum cross section and all the pieces have to be "listed"[by UL, for instance] as a grounding mean. Nevertheless, the maximum current it is limited to 600 A.
For 200 A the minimum cross section of cable tray it is 451.5 square mm [NEC Art.392 Table 392.60].
If you'll use a grounding conductor the minimum cross section is determined by the Size of Largest Ungrounded Service-Entrance Conductor or Equivalent Area for Parallel Conductors [NEC Art.250.66 Table 250.66].
Practically, a bare copper conductor of 95sqr.mm will be good -electrically and mechanically.
The grounding conductor impedance has to be low enough to permit the protection to be activated in a minimum short-circuit current case.
In order to minimize the touch potential you have to connect the tray to the support column by welding or grounding jumper so that each continue piece of tray will be grounded. Practically, one connection each 30 m it seems to be good.

 

[eliahud79]

thank you

the cables on the ladder are multicore cables, each cable have inside the grounding core.
i ask for the cross section of the extra gronding bare grounding conductor for grounding and for equipotential of the ladder only.

 

[7anoter4]

The cable tray has to be tested as per IEC 61537 or VE-1 for continuity. The grounding conductor from a power cable is insulated and connects the source Ground to the receiver [motor].Usually it is no touch between this conductor and cable tray. Nevertheless a live conductor could contact the tray as metallic solid contact or through a resistance. Also, since the cable tray has to be grounded at least both ends it could be a parallel path for the grounding conductor to share a fault current. A good practice it is to reduce the human touch potential of the tray by connecting it to Ground several times.

 

[eliahud79]

thank you