Buried Conduit? Choose Jackets that Resist Moisture
Water is ubiquitous in buried conduit. Cable jackets can help protect insulation.
Putting cable in buried conduit keeps the cable out of sight, and it's protected mechanically. But there is also a downside to underground conduit: water."Water from condensation and ground-water leakage at fittings contribute to high moisture conditions inside buried conduit," says Doug Ramsey, Southwire Electrical Division's vice president for industrial products. "In many installations, underground conduit is full of water most of the time."
Water increases insulation risk
The problem is that exposing cable insulation to water while the cable is energized can result in reduced dielectric strength which can lead to premature cable failure.
The first line of defense against moisture is an outer jacket that protects the insulation from direct exposure to water in the conduit. But if the jacket absorbs moisture readily, it will expose the underlying insulation to the absorbed moisture. The moisture resistance of the jacket then becomes an important consideration for underground applications.
When you're choosing a cable jacket, the wealth of options can be confusing. Moisture protection is very important, but other mechanical characteristics can also affect jacket choice. The comparison chart shows moisture absorption for two premium jacket materials: Southwire's low-smoke, non-halogen SOLONON™, and chlorosulfonated polyethylene (CSPE).
SOLONON absorbs less water
The Mechanical Water Absorption test was performed on the jacket materials following the procedures in UL 1581, section 1040. A 4" x 1" sample of each material was submerged in tap water at 70°C for seven days. As you can see in the chart, the SOLONON sample absorbed substantially less water than the CSPE. When CSPE formulations were revised to reduce lead content in the mid-90s, water absorption increased significantly.
The chart also shows other important jacket characteristics. SOLONON compounds give you mechanical protection and thermal ratings equal to or better than CSPE compounds, and SOLONON also has a lower coefficient of friction, which reduces pulling tension in conduit installations. You get easier installation and reduced risk of cable damage, which translate into higher reliability. In addition, SOLONON's low-smoke, zero-halogen rating gives you improved fire safety when the cable emerges into occupied spaces.
SOLONON's benefits of superior moisture resistance, greater tensile strength and reduced pulling tension look good even in industrial applications where smoke may not be an issue. "SOLONON is also environmentally friendly," says Ramsey. "What's more, you can count on Southwire to be here with the product when you need it."
Cable Jacket Comparison Chart
Solonon
CSPE
Moisture Resistance
Mg of water absorbed per square inch
(7 days in 70°C water; Lower numbers mean better protection.)23.1
43.2
Physical PropertiesUL-44
Tensile Strength (PSI)
Elongation (%)2000
1601800
300Oil Resistance, ASTM #2
Test Temperature (°C)
Time of Immersion (Hrs)
Tensile Strength
(% of un-aged value)
Elongation
(% of un-aged value)70
4
65
85121
18
60
60Coefficient Of Dynamic Friction (µ, in PVC duct; Lower numbers mean easier pulling.) 0.35 0.5 Limiting Oxygen Index
(Higher numbers mean more fire protection)40 30 Halogen Content (%) Smoke Density ASTM E662 (Lower numbers mean less smoke generated.)
Flaming Mode
04.0
DM
Non-Flaming Mode
04.0
DM2.7
59
21
178325
400
325
480Limited Smoke Test
(Pass/Fail UL-1685)Pass Fail
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