arcticguy00
Mechanical
- Feb 7, 2003
- 6
Has anyone in this forum ever experienced water becoming entrapped in a buried metal clad cable ? I am interested to find out of this is a common occurance; here's the situation:
About 6 weeks ago we installed two parallel 3 conductor 500MCM metal clad service entrance cables (with PVC jacket) for a 4160V service. The cables are direct buried in 4' deep trench with sand bedding. The cables enter the building below grade and run (exposed) horizontally in the building for about 100' then turn down and terminate into the top of a large distribution.
The cables were installed under wet conditions and the sand in the backfilled trench saw a lot of water before the Contractor covered the sand with a less pervious soil. The service was sized for a future load, and is grossly over sized at present, drawing less than 20A.
This week, during a routine inspection, the distribution was opened up, and we found water dripping into the distribution from one of the new metal clad cables. Just inside the MCC, where the aluminum armour had been removed to expose the individual conductors, moisture was found to be present between the armour and the polymer sheath that bundles the individual conductors. The moisture was observed to build-up until it formed drops. The water wasnt free flowing, but dripping pretty good with a puddle on the floor of the MCC about the size of 1/2 cup.
Questions:
1. Is this common in underground direct buried applications?
2. Is anyone aware of a field test that can be performed to verify the machanical itegrity of such a cable? Perhaps an air pressure test?
Maybe I should also post this question in the Plumbing Forum.
Thanks to all that read this far and to any who can shed any light.
About 6 weeks ago we installed two parallel 3 conductor 500MCM metal clad service entrance cables (with PVC jacket) for a 4160V service. The cables are direct buried in 4' deep trench with sand bedding. The cables enter the building below grade and run (exposed) horizontally in the building for about 100' then turn down and terminate into the top of a large distribution.
The cables were installed under wet conditions and the sand in the backfilled trench saw a lot of water before the Contractor covered the sand with a less pervious soil. The service was sized for a future load, and is grossly over sized at present, drawing less than 20A.
This week, during a routine inspection, the distribution was opened up, and we found water dripping into the distribution from one of the new metal clad cables. Just inside the MCC, where the aluminum armour had been removed to expose the individual conductors, moisture was found to be present between the armour and the polymer sheath that bundles the individual conductors. The moisture was observed to build-up until it formed drops. The water wasnt free flowing, but dripping pretty good with a puddle on the floor of the MCC about the size of 1/2 cup.
Questions:
1. Is this common in underground direct buried applications?
2. Is anyone aware of a field test that can be performed to verify the machanical itegrity of such a cable? Perhaps an air pressure test?
Maybe I should also post this question in the Plumbing Forum.
Thanks to all that read this far and to any who can shed any light.
