Cable combination for marine application

[BrianMuir]

Hi,
I have a marine project in front of me, and am getting frustrated with lots of conflicting recommendations for the cabling solution.

The problem is to get a 1200A 600A three phase service out to a barge which serves quite a few ocean based loads. Power will originate at a transformer close to shore, be fed about 200ft down cable tray attached to the side of a fixed pier. At the 200ft mark there is a break in the pier and for 90 or so feet it is a floating dock. At the end of the dock the cables feed directly into the barge where they terminate in an electrical distribution center permanently installed in the vessel.

The loads are a variety of motors, compressors and lots of other stuff and it will not be balanced completely across the phases. In other words, a neutral is required. A bond conductor is of course required as well.



I am looking at multiple runs of 4C ACWU (perhaps 500MCM) with internal bond to get to the 200ft point, a junction, and then flexible marine power cable from there to the barge.

I am receiving advice such as "don't use ACWU" near salt water". I'm not sure about this, the cable is protected by the outer jacket. Perhaps special care is required at junctions? ACWU is acceptable by code but is it worth the expense for TECK? It also seems that the flexible marine cable is only available in 3 conductor up to 500MCM but in four conductor only up to #4/0, at least from one of my sources. What the heck?

Also, as I understand it the marine cables are only in copper... What is the proper process for splicing the ACWU and copper?

Any advice appreciated.

 

[buzzbar]

I have done a lot of marina work, and I have determined that the best method is to use G or GGC cable. Go to this link:

http://www.southwire.com/products/TypeGTypeGGCRound.htm

It's approved for use in marinas (at least here in Washington State). It's great, because it's very flexible, and water tight, you can even submerge it.

In your case, I would run a continuous length of G cable for the entire run. Leave enough slack where necessary to account for the tides. Obviously, a continuous run is better because you won't have any junctions, which is where most problems occur.

The down side is that it's EXPENSIVE! But it's worth it.

Good luck!

Andrew (buzzbar)

 

[BrianMuir]

Thanks Buzzbar,
So, despite the fact that much of the run is on rigid pier you would still spec G cable. Interesting. And yes, very expensive.
thanks for your input.

By the way I did learn that out local inspector strongly discourages use of aluminum cable near the water. I don't think this is a code rule, but he is very experienced and I trust his judgement, so copper we go.

 

[buzzbar]

Parallel runs will be needed, for sure. The G Cable has a much higher ampacity, though, so you can use smaller wires than standard THHN CU. Table 400.5 (A)(2) shows you the ampacities. The labor savings is huge too, because there's no conduit. Just make sure you use sleeves through any structures.

Aluminum is a definite no no on salt water. I used aluminum mechanical lugs on some power pedestals once, and they were starting to corrode within a week or so.

Good luck!

Andrew (buzzbar)