Can I fill and underground rigid pipe with silicone?

[big john]

I would not fill the pipe with silicone. For one thing, I don't think it will stop the leak, in addition to making the raceway virtually useless in the future. I have also seen the damage that even a small amount of curing silicone will do to copper conductors and wouldn't want anything to do with putting an entire tube in a conduit.

I have used the Polywater product successfully in the past, but for me that would be a last resort because water is notoriously difficult to hold back permanently.

First choice would be find a mechanical solution to prevent the water from reaching the panel. Come in above grade, arrange it to drain, changeover to direct-burial cable, whatever.

 

[Jon456]

I see you are in California, but if you leave that water in the pipe in cold climate areas it will freeze and burst the pipe open.

If you read the thread I linked in my post, you will see the procedures used for performing the test (including the fact that I foam sealed a hose alongside the wires in the bottom of the conduit so I could fill the conduit for the tests and so I could drain the water out immediately after the tests).

Furthermore, I completely removed the plug after the wet megger testing was completed. No water was left standing in the conduit at any time.

 

[tom baker]

225.27 Raceway Seal. Where a raceway enters a building
or structure from an underground distribution system, it
shall be sealed in accordance with 300.5(G). Spare or unused
raceways shall also be sealed. Sealants shall be identified
for use with the cable insulation, conductor insulation,
bare conductor, shield, or other components.

This is one of my changes for the 2014 NEC adding conductor , bare conductor... Polywater FST is the product that is identified for this, silicon is not.