480V Single Conductor Sheathed vs. Unsheathed Generator Cable Question

[tumbleweed1]

Before anyone says- I've already completed a search on here for info about sheath grounding. Regardless, I still have questions.

Situation: Parallel 480V generators placed 25ft away from switchgear. Some applications have ~400A/phase, some applications have 1800A or 900A/phase in parallel runs. All cable is ran with 100% spacing (up to 1.6" cable OD) in open aluminum ladder tray.

If I were to use braided bronze-armoured tray cable w/ 2kV insulation, my installation method would be to have a 1/4" thick aluminum gland plate at the generator terminal box, complete with aluminum cable gland per phase, not armoured cable connector, but like a Kellem Cord Connector/Strain Relief. On the switchgear end, for the <400A applications I would also use the same aluminum gland plate treatment. For >400A, I would use an insulating glastic material as a gland plate, still with aluminum cord connectors.

Thing is, using these strain reliefs wouldnt allow me a means of grounding the armour. So using armoured cable connectors seem best to use on one end for grounding.

Using non-armoured cable approach, first, would that even be good for the larger ampacities? I suppose at smaller ampacities <400A that may be ok, but I understand that armour helps to minimize capacitive charging current. If the insulation is rated for it, would it still provide a touch-hazard? Any other adverse effects? I dont anticipate physical damage being an issue here.

Armoured Cable: Page 3

http://almascable.com/DataSheets/OilRig-Type P-Draka.pdf

Type of Unarmoured cables: Page 7

http://www.generalcable.com.mx/catalogospdfs/17-MOR_POLYRAD_CABLES.pdf

 

[waross]

I don't often use aluminum gland plates. As long as each group of A, B, C, Neutral enters through the same hole, there is no encirclement and no eddy currents.
As an example, for three conductors per phase I punch a row of holes in the steel enclosure and then cut slots to joint each A,B,C,N group.[tt]
A B C N, A B C N, A B C N
0-0-0-0, 0-0-0-0, 0-0-0-0[/tt]
A separate conductor is used for equipment grounding.
An alternative to avoid issues with high currents on grounding conductors, three grounding conductors may be used arranged thus:[tt]
A B C N G, A B C N G, A B C N G
0-0-0-0-0, 0-0-0-0-0, 0-0-0-0-0[/tt]
The magnetism sees this as one hole and is not concerned with the shape. This avoids encirclement. The fields of each group cancel.
Be sure to use non ferrous connectors and lock-nuts on each end.
At the load end it is good practice to insulate the sheath, armour or braid.
I have done this in non hazardous and dry indoor locations by wrapping the end of the armour with varnished cambric tape and then clamping it in a dry type connector.


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

 

[ScottyUK]

Brass has equivalent magnetic properties to aluminium but without the tendency to gall up and fuse a gland into a solid inseparable mass. If you have an aggressive environment you might get intermetallic problems with aluminium armour in which case an aluminium gland would be a better choice if you can accept its other problems.