heavy rainfall underground cabling

[dicker911]

I have recentley contracted with a Costa Rican electrical firm for underground install. 240v/ 125amp per pvc conduit/ from 75kw trans. concrete boxes w/metal covers. #000 shielded aluminum. some boxes are not drainage prepared. Some cables are longer than others. Some runs are 300+ meters. Yesterday they placed foam filler at the ends of all conduit tubes. also the possibility that water may have entered some conduit during install may have occured. What suggestions do I give my installer to stabilize this situation. What other info can I provide. Why are these issues important.

 

[davidbeach]

What is the issue? All underground installations are assumed to be full of water by code.

 

[dicker911]

Thank You davidbeach. Is there a concern over unequal lengths having thermal problems? Will ther be exspanion or contraction issues? Or cooling issues of any concern?

 

[wareagle]

If you have parallel cables, the unequal length will come into play. The current will not divide equally. Not sure from you post if this is the case.

 

[davidbeach]

The only time different lengths become a problem is when they are connected in parallel. If they are different phases of the same circuit there is not a problem as long as the difference are with in reason. If they are in parallel you can get in trouble with unequal loading for seemingly minor differences in length.

 

[dicker911]

Thanks every one for your help. We do NOT have 3-phase power. so would removing the runs and remeasuring be the answer??? How critical is the distance issue , inches per meter ratio? inches for 10 meters, inches for 100 meters???

 

[davidbeach]

What conductors are of different lengths? If they aren't in parallel (solidly electrically connected at both ends) there is no issue.

 

[sslobodan]

They were supposed to close cable ends with bitumen (easy to remove and water proof) It is general trick that every cable jointer on Earth knows. It can withstand for months (even years) before installation is completed. If they put that (or something similar) than you don't have problem with moisture. If not you should check cable endings for dielectric permeability (Cut one 10 cm long than run test on permissive voltage if it passes you might be assured that there is the chance for all of them are OK.

The recepie for bitumen closing is: heat bitumen in tuna can (cylinder shaped any shop ) and just put the end of a cable in it. Bitumen is easy to heat and will cool down easily and fast. after this is done you will have good protection from moisture in cable until installation. This may sound funny to someone, but I saw that recepie in many countries all around the world and cable jointer's are all agree it is best and cheapest way of finishing such job.