Seawater submersible (1.5 meter) low voltage power cable.

[BlackJackJacques]

Gang, I have an application for a 50-meter 460 V cable run subgrade in ASSHTO class heavy grade precast concrete culvert with cast metal grate. The area is subject to periodic storm flooding to about 5 feet over grade. Many of the US cable manufacturers are telling me that their standard above-grade products, such as DLO, Exane, Type P, etc can perform underwater, despite there being no subsea rating. One manufacturer who makes subsea MV cable indicates they can also modify their run without problem and make their low voltage product, water-tight. Can anyone recommend an LV subsea cable?
A side question, is there any reason I'm missing why I can't run an MV subsea cable for LV service?

 

[waross]

A side question, is there any reason I'm missing why I can't run an MV subsea cable for LV service?

Cost?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

Moisture absorption seems like an issue for most thermoplastic cable insulations involving immersion. Thermoset materials perform better. Cross-link polyethylene cable works well in immersion.

 

[FacEngrPE]

If this is an active storm drain that can pass flowing water, the cable may need to handle the mechanical loading that might result from the flowing water.
Tugboat's observation about permeability of insulation is the same as mine. Below grade conduit systems often are full of water, and sometimes mud, so water resistance is almost always necessary. The result of picking a moisture permeable insulation is conductor corrosion.

Fred

 

[BlackJackJacques]

Cost is not a great issue in that the alternative would be to run an overhead bus duct, and I would normally select to run an overhead bus duct in this case but for the heavy machinery traffic and vulnerability of the posts supporting the bus duct structure - ergo the subgrade approach.

The concrete culvert is not an active storm drain in the sense of its primary intention but will drain rainwater, sheet flow, and of course, receding floodwater. Additionally, the width of the culvert is about 48 inches and the cables will be elevated several inches off the bottom.

 

[TugboatEng]

I believe cables meant for immersion will have a layer of water blocking tape under the jacket.

https://geca-tapes.com/applications/power-cable/

I would look in to a marine class society approved (American Bureau of Shipping or DNV are the leaders) cable with low smoke insulation. The low smoke cables typically use some type of TPE or CPE insulation and are available with the water tape. The cost should be reasonable if you get it without armor.