Cable Splice Box Grounding and Concentric Neutrals

[Amex12]

Hi,

I have a project that involves splicing an MV cable at an underground splice box. The cable concentric neutrals are going to be grounded at either end. My question is if a ground loop and rods are required at the splice box? My thought is that since the current will flow back through the concentric neutral wires, introducing a ground grid would have us required to investigate step and touch potentials at the splice box.

Your thoughts are appreciated!

 

[7anoter4]

You will need to choose the most suitable grounding method to avoid energy loss and overvoltages.

 

[Amex12]

@7anoter4, I don't think this answers my question. I am aware that grounding both sides of the cable will cause circulating currents and have a play in derating the ampacity but I want to know if a small grounding system is required at the splice box.

Thanks

 

[Kiribanda]

In my opinion you donot need a grounding system with a grid at the splice location.
But you have to make sure that the screen/ con neutral are PROPERLY bonded at the splice
and continue without any break between the starting & end points of the cable. By doing this bonding
and continuation you are providing a galvanic return path to the ground fault currents back
to the source. That means you are avoiding GF currents going into the soil which will finally create
step & touch potentials. Therefore you donot need a ground grid.

 

[7anoter4]

If you don’t ground both ends you get a upbuilded voltage at ungrounded end. This voltage is limited-it depends on local standard-from 25 V-usually [up to 200 V in some countries]. If you ground both ends or in other points a circulating current will reduce the ampacity [of the main conductor]. The splice has to be grounded in order to avoid touch [and corrosion may be].
In order to avoid induced voltage or circulating current it is indicating phase cross bonding. In order to avoid transient over voltages at joint point you need probably a sheath voltage limiter (SVL) if the shield is not grounded here.
Some special bonding options include the following:
Impedance bonding
Sectionalized cross bonding
Continuous cross bonding

 

[waross]

There may be issues with the junction box rather than the cable itself.
Code and good practice both dictate that any conductive electrical equipment be grounded.
This includes junction boxes.
If there is an equipment grounding conductor running with the cables this should be connected to a conductive junction box.
If there is a neutral conductor there may be issues with protection devices caused by adding another ground point that was not anticipated by the original designer.
Suggestion: Use a non-conductive splice box.
Suggestion: You may be able to reduce your induced voltages and currents by cross connecting the concentric neutrals.
It depends. If the splice is to be near either end of the run then cross connecting the neutrals will yield little effect.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

If governed by NESC, you do not need a ground grid at the splice box because it is not an electric supply station. You may get some touch voltage during a fault if you stand next to the box and touch something bonded to the ground rod. This is no different from standing next to a distribution pole with the neutral connected to a ground rod and touching the ground wire on the pole.

 

[OffTap100]

This Delta or Wye?