Cables-3C and 3-1C

[tctctraining]

I have an application that I need to feed a 5MVA-27.6 Kv transformer through a switch. I can use a 3 X 1C cable or a 3C cable . I believe code has installation restrictions for non-armoured cables to be either inside a conduit or inside an enclosed cable trays.

Beside bending issue that we might have with triplex cables , what are other major concerns to consider when picking between triplex and 3 X 1C cables?

 

[waross]

Purchase cost.
Installed cost.
Special treatment for three conductors to address sheath currents and eddy currents in enclosure iron.

Bill
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"Why not the best?"
Jimmy Carter

 

[tctctraining]

We usually bundle all three sheath wires and ground it at the switch location. Will bundling three concentric neutrals and ground it have the same effect as if you have one concentric wire for 3C cable and ground it?

 

[rcw retired EE]

The three high voltage conudctors inside a 3-C cable will each have a concentric shield. The overall jacket may or may not have a metallic shield, depending on the design. If it is an armored cable, the armor makes on overall shield that needs to be grounded.

If you run three single-conductor armored cables and ground the three armor terminations at each end it will create circulating currents.

Three conductor armored cables should not create circulating currents.

 

[tctctraining]

In existing installation, bare copper wire shield is grounded at both sides ( Switch and transformer). There are no LA used at each sides and distance between transformer and the SWGR is below 100'.

So if we replace the existing 3-1C cables with a 3C cables (as per attached) then we need to ground the " Tape Shield (E)" at both locations right? considering the short distance, I assume the cirulting wire is not an issue.
"Ground Conductor (G)" acts as a bonding conductor.