earthing of cable armour

[144x]

all the cables used in a substation are armoured .which end of the cable armour should be earthed.inside control and protection panels or in the marshalling kiosks at the switchyard?
thanx.

 

[bigamp]

I have only ever seen that the SWA is earthed at both ends, via the glands and the earthed panels/cabinets.

The only times I have seen that only one end is earthed have been:

(1)When cabling from site to site and you need to keep the site earthing systems isolated from each other.

(2) For some instrument signal cables. From memory it was thermocouple cable.

 

[jghrist]

Power cable shields and armour are generally grounded at both ends to limit induced voltages from current in the conductor. This is not a problem with control cables, however. I'm not familiar with using armoured cable for control cables, but control and signal cable shields are generally grounded at one end only to prevent currents from flowing when there are potential differences in the ground system (faults, lightning). I would assume that armour grounding would follow the same philosophy. Shields are normally grounded at the receiving instrument end.

 

[dpc]

For saftey reasons, I'd be inclined to either ground at both ends, or ground only at the control panel end. Grounding at the field end could result in a voltage to ground existing on the armor at the panel end.

If this was an installation covered by the NEC, the armor would need to be grounded at both ends, I believe.

 

[144x]

if we think of armour as shield there is a paper from GE "Theory of Shielding and Grounding of Control Cables to Reduce Surges"that says grounding at both ends is the best practice for both reduing the surge voltages and also eliminating electric and magnetic field transients.but most of the engineers belive that single point earthing for control cable is the best practice.