intermediate terminals of CT secondary cable shield grounding

[odlanor]

Our criteria for CT secondary cable shield grounding is:
- For power house: cable shield grounded at the one ends.
for outdoor substation: cable shield grounded at the two ends.
The route of the CT secondary cable is not straight from CT to relay. There are intermediate terminals.
The question is:
can we assume sections of shielded cable for grounding, or we must keep shielding continous?
We prefer sections like:
1-shielded cable from CT to junction-box1: Grounding at CT;
2-shielded cable from junction-box1 to junction-box2: grounding at junction-box1;
3-shielded cable from junction-box2 to relay board: grounding at junction-box2;

 

[davidbeach]

Shield should never be grounded at both ends. For safety sake, I'd always ground the end closer to the relay.

 

[odlanor]

davidbeach,
I think you're contradicting yourself or I am not clear. See thread below:

davidbeach (Electrical)
18 Jan 06 18:45
waross, CT cables have to go from point A to point B. Point A is where the CT is located, very little choice as to where that might be, and a brutal electromagnetic environment, particularly during fault events. Point B is somewhere else, a control room for example, where things are much quieter electromagnetically. [li] The shield must be grounded at both ends[/li], possibly elsewhere also, .........

The route of secondary cable has 3 cable-sections interconnected.
Should I connect shield of each 3 section and grounding both ends
or
ground one end of each shield-section? This solution is better for installation.

 

[davidbeach]

Interesting. Not sure why I would have said that. On the other hand, if both ends are grounded to the same ground grid, where a relatively high impedance shield is paralleled to a relatively low impedance ground grid there shouldn't be much trouble, but if there is any possibility of significant current on the shield, normally or during fault conditions, that unexpected current can create problems.

 

[stevenal]

IEEE 525 Annex G recommends grounding the shield at both ends. If run far from ground grid conductors, then run a dedicated ground conductor in parallel. Also says to keep the shield intact, so I expect you should keep it continuous.